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Discussion Starter #1 (Edited)
I just experienced a failure of my idle actuator (IA). I have decided to replace it myself. To help you guys, I have decided to do a little write up of the phenomenon and how I went about correcting the problem.

The issue manifests itself with a DSC failure message on the center console, along with a start assist failure notice. Obviously, it throws a CEL and puts the engine management software in 5k RPM limit mode. However, the car is still drivable. Data logging confirmed for me that the DME has the throttle actuator (TA) of the failing bank take over, in my case on bank 1. The IA1 on bank 1 is fully off line. (I might post some of the curves I took later.) However, you must understand that the car is still drivable -without risk- of damage to the engine, albeit that is runs ever so slightly rough at low RPM, as many be expected. This may be worse depending on the state of the notorious TAs in your car, which develop 'play' in the gears and will expectedly make the idle that much more rough. Mine are new, so no issue there.

The fault code is CDBD - U1138: Idle actuator CAN message, bank 1. Message Monitoring Idle-Speed Control Valve DPR Overwrite Error (Bank 1).

The issue can obviously be caused by a bad connector on IA1. However, since the CAN bus to IA1, IA2 and SMG in a non-manual car is shared, being still in control of the IA2 and SMG will confirm that the CAN bus and DME are not the culprit. It is very likely we simply have to replace the IA1 because for some reason it fails the pre-drive check where the IA1 is failing its initial response to the DME for some reason. I do not expect cable & connector issues because I was able to test the IAs in ISTA+. I could hear it operate with the engine off (off course). Note that testing forgoes the pre-drive check and thus the DME does not shut down IA1. Yes, it is the DME that DECIDES it does not like the IAs or the TAs. I have proven on my TA software writing experiments that suppossedly "broken" TA does still work. TA and IA are controlled in the same way, but on a different dedicated CAN bus for the TAs.

When I ran IA1 and IA2 tests in ISTA+ it resulted in IA2 not meeting operational test requirements and IA1 does meet requirements (!!). Needless to say, this test is somewhat unreliable. I will proceed and replace both of them as destiny is clear here. Here are some screen captures. Unfortunately, they are rotated and my Adobe Acrobat Full Version refuse to rotate them counter clockwise. So, you will have to put up with that for now until I get smarter.

I found replacement actuators available from Rockauto.com for $440 a piece. They are branded as Airtex/Wells, but I just got them and as was anticipated they are repackaged VDO/Siemens units. Beware that this does NOT come with the required gaskets; It does have the rubber seals installed. So, order them separately from BMW. I also ordered new air inlet hoses as well as vent valve hoses. With 82k mi. on the counter replacing hoses is a good idea, especially in winter. Don't cheap out too much.

I will conduct this repair later this week and report back. Stay tuned. I will provide lots more pictures and details.

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I recently had to replace my idle control valve with a CDBD code. It isn't too hard but its tight in there especially with the middle wiring harness still in place. GL!
 

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Discussion Starter #3
When I did my TAs I disconnected the wire harness entirely and lifted it out of the way. Should not be much of an issue after that. Did you know you can do that?
 

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Awesome stuff man, and nice to see the bmw actuators for so cheap aswell! Cant wait to see the rest.

When I did my TAs I disconnected the wire harness entirely and lifted it out of the way. Should not be much of an issue after that. Did you know you can do that?
I see alot of people do not do thism only a hand full have removed it and has cleared so much more space.! Might be a small DIY to add to this for us, i haven't had to tackle this myself but i would remove the harness entirely if i did.
 

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When I did my TAs I disconnected the wire harness entirely and lifted it out of the way. Should not be much of an issue after that. Did you know you can do that?
Yes I knew you could remove it but not how. I took out the front 10mm bolt but there just seemed to be so much more connected to it I didn't feel like digging it out more. Tips or a diy w/ picutres?
 

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Discussion Starter #7
New IAs are in. Taking a break. Tomorrow, I will throw some new sparks as well now that I have the top off. Makes it so much more accessible.

ImageUploadedByAutoGuide1484441374.369523.jpg
 

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Discussion Starter #10 (Edited)
The connectors are supposed to be attached to the wire harness box after they are clicked together. However, the plastic is so flimsy and brittle that these attachment literally crumbled off. I do not like to let them hang there. So, this is the way to keep them in place close to where they belong. Both IA connectors and bank 2 TA position sensors snapped. Big pain. But this will do.
 

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The connectors are supposed to be attached to the wire harness box after they are clicked together. However, the plastic is so flimsy and brittle that these attachment literally crumbled off. I do not like to let them hang there. So, this is the way to keep them in place close to where they belong. Both IA connectors and bank 2 TA position sensors snapped. Big pain. But this will do.
Same thing happened on my car. Had to zip tie them back to the harness. Maybe the wrong place to ask but what spark plugs / gap # did you use?

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I have to do my thermostat I guess I'll change the gears out on mines and regrease the TAs and TB linkage while I'm in there


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Discussion Starter #15 (Edited)
Same thing happened on my car. Had to zip tie them back to the harness. Maybe the wrong place to ask but what spark plugs / gap # did you use?

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I got the spark plug specifically made for our engines. That is: NGK LKR8AP (4471) Laser Platinum. No need for re-gapping. I only had 21k mi on them but I felt I needed to replace them. Here are some pictures of my spark plugs. Also compare it to a new one. I am not really -liking- the crud on the ones that came out of bank 1 (1-5). But I think it is okay: Spark Plug Analysis

Any advise?
 

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I got the spark plug specifically made for our engines. That is: NGK LKR8AP (4471) Laser Platinum. No need for re-gapping. I only had 21k mi on them but I felt I needed to replace them. Here are some pictures of my spark plugs. Also compare it to a new one. I am not really -liking- the crud on the ones that came out of bank 1 (1-5). But I think it is okay: Spark Plug Analysis

Any advise?
What kind of gas do you run octane and company? Ever added additives, octane booster or cleaners?
Not saying there is an issue was just wondering.. The color of the plugs and burn pattern all look good, a little build up of sludge-ish material, seems harlmess.
 

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Discussion Starter #17
What kind of gas do you run octane and company? Ever added additives, octane booster or cleaners?
Not saying there is an issue was just wondering.. The color of the plugs and burn pattern all look good, a little build up of sludge-ish material, seems harlmess.
I always run Shell 93. Part of my route. No additives or other steroids. I think these are just ashes that are the result of burning small amounts of oil. A known fact for these engines. Plugs are not burnt mechanically. So, I guess it is alright.
 

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Nice post, can't wait for the writeup.
 

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Discussion Starter #20 (Edited)
Steps to fix the Idle/Throttle Actuators

When you have a throttle actuator or idle actuator fail, this is the typical dashboard you are presented with. You get a CEL: Check Engine Light, along with this pretty half filled engine symbol indicating that you are now running a limp mode engine program. The engine feels sluggish and you are limited to 5000 RPM revving. The center console will give you the DSC (Dynamic Stability Control) malfunction. Aside from that you get the Hill Start Assist error in you center console when you hit the brake pedal for the first time. These errors seem unrelated. However, they are because failure of the Intake Actuators and/or Idle actuators will result in the engine not being able to produce a guaranteed intake vacuum. This vacuum is needed for brake assist. The DSC and Hill ascent control systems rely on this as part of their control. So, now it all makes sense.



The idle actuators control engine air intake up to about 3000 RPM after which the throttle actuators open and let the bulk of the air come in. When an idle actuator fails, the throttle actuator takes over fully and the IA is taken offline by the DME. Hence the higher idle RPMs in limp mode to ensure the idle is relatively smooth. Thus the car continues to drive after a slight hiccup during the transition such that you get home and get some time to order parts. Beautiful thing.

I ordered 2 new idle actuators despite the fact that only the bank 1 IA failed. But, we all know better and as you will see this is a bit of work. I ordered my new IA through rockauto.com. I ordered the ‘Airtex’ edition, which is nothing more than a repackaged VDO/Siemens unit. Thus, original equipment for 440 bucks a pop instead of $700 or so. Here is the box (contents were shown in the previous posts):



Lets get to work. When the plenums are to be removed, create yourself maximum space by removing the bulkhead entirely. It is simple and quick. Especially after a couple of times! In the pictures below I use yellow arrows and marker to point some of the things I am talking about. All the yellow arrow in the picture below point to the components of the bulk head: Air filters and ducting. Start by pulling the yellow bumper (3) off. Just pull off and take it out. With everything you remove, always pay close attention on how things come out such that you can pout them back properly. Take some picture to help yourself where needed. Take the air filter off the bulkhead. Unlatch the spring clip (a metal bar). Rotate 1 plastic “bolt” on each side by simply turning 90 degrees. There is no thread; just turn it counter clock wise. If it takes force, you are doing it wrong and are about to break it! On the passenger side, disconnect the hood switch and pop it out of the bracket on the filter box. Plug the switch back on the harness to avoid loosing it. Twist the air quality sensor approx. 45 degrees to unlatch it. Lay it to the side. Be gentle or you will replace this too. Take the air boxes out put them away. You won’t need them for a while



With the aforementioned items removed you get to the picture below. Time to remove the rest of the hoopla. Remove the plastic water guides on the left (3) and right (4). Pay close attention as to how to put them back. Remove plastic connection bar (5). Slide towards the passenger side while holding up the retaining latch. Take a close look at the part to find this latch. Remove the 2 torx screws at (1) and (2). Don’t drop them or you will be sorry. (Tell us about it when you do such that we all can get a good chuckle.) Loosen 3 more 90 degree plastic bolts (middle, left side and right side). Starting with the passenger side, lift up the plastic trim piece and slide towards the middle. The right side is removed in the opposite direction. You just created yourself oodles of work space. Also handy to replace the spark plugs and thus, while I was in there, I replaced these buggers too after all was set and done. All of this is covered in another DIY, without this little bulkhead tip.



Alright, on to removing the air boxes. I do not have very detailed pictures on the procedure here, but most of you know this. Release the spring clips all around the air boxes. Be careful, sometimes they pop out of the retainer and fall down. So, I usually catch them with a finger popping them loose with a screw driver. Release the strap on the plenum side. Unplug the MAFs. No lift the air box and slide it from underneath the coolant reservoir overflow hoses. Be patient and gentle in this process. If it takes force, you are doing it wrong. Release the 2 bolts on the coolant reservoir at the yellow arrows (1) and 1 lug on the air box.



Lift up the coolant reservoir. Unplug the coolant level sensor on the bottom of the reservoir (and don’t forget to plug it back in when you put it all back together). The next step is to remove the bottom halve of the filter box. Two torx screws; not shown, but straight-forward enough. Put the coolant reservoir of to the side. Secure it with a bungee or the like to avoid stressing the hoses too much.



On to the other side. Remove the filter box here too. Loosen the hose to the plenum on the plenum side. Disconnect the MAF (4)…. Etc. etc.;much the same. Disconnect the secondary air hose in the back of the filter box (3). Remove two lugs (1,2) to remove the bottom part of the filter box. Done. One more word about the two MAF-connections: Make sure you fold them away from the plenums. If not, and you put the plenums back on later you may end up sandwiching it between the throttles and the plenum. And you may have to remove the plenum again. Almost happened to me but I caught it in the corner of my eyes. In order words check every step you make.



Remove the rubber connection (1) between the plenums. It is tough to get off. I have an old screwdriver that I bent at the end 90 degrees with some MAP gas. Handy pry tool that prevent damaging this and makes for quick work. Don’t drop it! Later you can pop it back on by hand. Don’t forget it.



No for a very important step: Loosen the two oil return hoses (1, 2 from the CCV) behind the plenum. This is the reason for removing the bulkhead; impossible to get to without it being removed. If you forget to disconnect these hoses, they will break when you pull up the plenum from the front. And you are screwed! These hoses can only be accessed for replacement by lowering or removing the transmission. Don’t believe me? And be careful, even though you loosened them, because they are made out of stiff plastic they have a tendency to re-engage. So, be sure to make sure that does not happen.



Next step is to loosen the two vapor recovery hoses on each side on the rear of the plenum. The bigger hose (2) is attached with a spring clamp. The smaller hose (1) is attached with a crimp clamp that cannot be reused. Since I have had these plenums off before, mine has a nice screw clamp aimed such that I can easily loosen it. You will have to clip off and destroy the crimp clamp and replace it with a (stainless steel) screw hose clamp. Much easier, because you know, we all will be back here some day driving and M5.



Same deal on the other side (1,2). My recommendation is to take the spring clamp of the bigger hose, as it tends to crush the hose when not mounted on the plenum. But, don’t drop it. In the picture below I also marked the plenum markings that show where the screws are accessed for the hose clamps that hold the plenum on the throttle bodies. There are 5 of these on each plenum. Look under the plenum under that mark and you can see the screw. Loosen all 10 screws. I recommend approx. 5-6 full turns each of then to prevent them falling apart. I use a flexible tool for this job that grabs the screw on the outside. If you use a long screwdriver it will work, but you keep slipping of the screw; a pain in the ***, specially tightening them!



Before you lift up the right side plenum first, loosen the IA hose (1) just under the front of the plenum. Now, if the plenum has not been off before, or at least it was a long time ago, it is going to be stuck on the throttle bodies like it was glued. Slowly work it loose from the front. It may take a little gentle pulling. Make sure those hose clamps are truly loose; check again on the oil return hoses in the back! After the right side comes off, pull the left (passenger side, US) off. Same exact deal except that this box hooks onto the engine harness in the back. Lift it up and move it out towards the front of the car. Don’t forget the IA hose (1) in the front.



Because the IA and TA are under the engine harness box, the engine harness box has to be folded away to access them, at least partially lifted up to reach under it. Practically, most of the connectors have to come off. That includes the battery connections to the starter motor and the alternator, coming from the main battery feed. With high power wires like these flopping around, I rather disconnect the battery to avoid an unintentional welding session. So, it is best disconnect the battery negative as shown in the two pictures below. Because the cable is stiff, I put some insulation between; you don’t want the cable to pop back on the terminal by accident. Tape it down to be sure it stays where it belongs.





The engine harness box is held down by a bolt in the front, a lug in the back and the battery terminal on the driver side front. In the picture below the wrench is on the bolt. Take it out to loosen the front bolt secured on the thermostat housing. Loosen the lug in the back. Now, take a very close look behind there with a small mirror as there are two bolts. One of them is for the engine harness box securement; the other relates to a coolant pipe. And if you take the wrong one out it, you will likely have a hell of a time putting it back.



Now, because you almost work blind in the back of the harness box, I used some stick goo in my socket to make sure I did not drop the lug once it came loose. It is also to put back later as it will not fall down. See the next picture. Get your chewing gum out!



Time to unplug the entire harness. But before we do so, you need to take the protection covers off the ionic modules on the left and right. Two bolts each. This allows you to unplug the large connectors. Pull on the Tyco connectors at point (1) with a bit of force. The connector will slowly lift of the ionic module. Do both sides. Next loosen the big black lug on the battery connection. There is also a hex bolt on a retainer piece above it that has to come out (not shown). The bolt-hole is just ‘east’ of the battery terminal (2). Pull the jump terminal connection off. DON’T FORGET to put this back in the right spot later or else….. you will be sorry.



The 2 harness box securement locations are shown again in point 1 and 2. Disconnect all the harness box connectors. Work from the front to the back. Connection A is the main battery terminal we dealt with before; it should be loose already and the ionic covers & connectors (3, 4) should off already. Remove connectors B, C and D by pulling towards the front of the car. Do not pry with a screw drive or anything like that. Plastic pieces will break off. The harness box is exposed to high heat all the time and the plastic tends to become very brittle. I like to mark connector B towards the alternator with some (blue) tape to avoid accidental cross plugging with C later. E disconnects the throttle position sensor for bank 2. It is hidden under the cable harness box. It is attached with a slide-in clip. Much like connects H and G which you actually can see. Slide it out trying not to break it and then carefully disconnect the connector ends. Depending on the age of the car this might be a bit hard. Be patient. Don’t pry with screwdrivers. The slide out broke in all 3 positions, hence the tie wraps. I have been here before when my throttle actuators were shot. Disconnect the coolant temperature sensor (F). Slide up the metallic clip first, partially, not all the way out and then pull the connector off. Don’t loose the clip. It tends to come out and shoot away. Disconnect the idle actuators G and H. Disconnect the throttle position sensor for bank 1 (L). Loosen the starter motor lug K. Disconnect bendix connect J on the starter. It is the same type of connection as the temperature sensor F. At this point you can fold the harness away to the driver side.



Now we finally can take the idle actuators out. I replaced both. As you can see the IA’s are installed on thread inserts and you loosen the lugs to take them off. However, you need to slide them off after that. Well, after some fumbling I came to the conclusion it is a bad idea to start with bank 1: when you slide IA 1 off it bumps into IA 2 and you cannot get it out. At least, I could not. Now you have to push it back in. A *****! So, follow my advice: Take the bank 2 (driver side) THROTTLE actuator out first to give your self some more room to work with. 3 bolts at the base. Unclip the actuator rod. It just snaps off the joint with come care. Then take the bank 2 IDLE actuator out next. Yes, in that order. After you slide IA 2 off the lugs you can make the turn towards the front of the car and lift it out. Of course, the hoses have to be taken off first. The big IA intake hoses that connect to the front of the plenum and the small hoses that connect to the tank vapor purge valves (2x). In my case, that little hose was rotten stuck on the badly corroded IA. I cut it off to make it easy on myself. It has a hose clamp on the purge valve that needs to be pried off and cannot be reused. Make sure you have two new hose clamps available. In my case, I replaced the intake hoses as well as the purge valve hoses with new ones. Good that I did, as this little hose would have stalled progress of a week waiting for them to arrive. Pfff.



When you pull the old IAs out for the first time, you will notice it will fight you a bit. That is because the deal has deteriorated and has partially adhered itself to the head. Look at the residue of it sitting in the hole at (A). To ensure the new gasket ring seals properly this has to be cleaned up. Make sure that the crap does not go into the engine. Also, do not use abrasive tools. I worked it literally with my nails and a flash light. A soft plastic scraper could work also. Also clean up the front surface of the IAs, right where the steel gasket sits between the IA and head.



As you can see the steel gaskets have become very rusty. The aluminum next to it is corroded and pitted as well. I gently smoothed the surface a bit by scraping but there is very little you can do getting is back to perfect. Note that the steep gasket is there to avoid the IA “welding” itself to the heads. It is not meant to be an air seal. The rubber gasket does that part. Here is a new and an old gasket together. Replace them; don’t reuse them. Beware: These gaskets do NOT come with the new IA’s. Order separately.



Both IAs are put back in place working in reverse order from before. Bank 1 first, then bank 2. I put a little bit of glycerin on the gasket such it would slide in a bit easier and to avoid marring the gasket. Don’t forget the washer brackets. I reused the old ones. I wanted to properly torque them, but the head of my cheapo torque wrench would not fit in between the IA. So, it was a blind torque. Hallelujah! By the way, make sure you have plenty of small ratchets, sockets and extensions on hand for this job. You need them. Note that the throttle actuator is not back yet in the picture below.



And now the TA is back in. You can torque this properly. Make sure the IA cable harness poke up, such that you can reach them later when you connect everything back up.



Install the new purge valve hoses with new hose clamps on the purge valve side. Stainless is the way to go. Put the big intake hoses back on the IA’s. (Not shown).

You now have replaced the IA. Reverse everything I told you so far and put it all back. Do not forget to connect battery connections properly.



A closer look of the still good bank 2 IA.



And the bad one: I will tear this puppy down later to see if I can find root cause. Note the little piece of plastic sitting near the butterfly valve. The hose end is still stuck on the IA. It is really stuck!



And everything back together just before putting the plenums back on. Fresh tie wraps for the 3 aforementioned connectors. And everything wired clean.



Before you move on and put the plenums back on, re-connect the battery and run the IA actuator and TA actuator tests in ISTA/D. This saves a lot of time when something is wrong. Do not start the engine of course. Just turn on ACC and apply electrical power to the engine. Find the procedure in ISTA/D and run it. Make sure all IA and TA pass. Mine did, lucky me. You will get extra engine codes: The MAFs are disconnected, so do not be surprised. And the dash will throw you a coolant low symbol because the reservoir level sensor is still disconnected. After you put it all together, clear all the codes. Start the engine and when all is well drive it for a bit to test the behavior. Read the codes again when you come back to be sure everything is fine.

I hope this is of help for anybody endeavoring replacing anything inside the engine V. Throttle actuators and Idle actuators and more. Doing this myself probably saved me $1500 bucks or so. Worth the annoyance. It took me 8 hours in total. And I call myself somewhat experienced at this point.
 
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