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Discussion Starter · #1 ·
Hi All,

Lately I have been traveling a lot for business. What I noticed is that after my car has been sitting in the garage for three days or more, a peculiar throttle issues comes up for a little while which then goes away.

It is as follows:

The car drives fine for like 10 to 15 minutes, then all of a sudden the throttle response gets choppy , especially in the lower RPMs where the drive becomes really jerky. Also the car start idling really rough. Not sure if it's fuel pump related or something else.

Again after like 30 minutes of driving or so, the problem goes away fully and if I drive the car daily it never shows up.

So since it has something to do with the car sitting in the garage, I wonder if it is related to some of the sediments in the fuel clogging anything up. What I find quite strange is that it doesn't happen from the get go and it takes 10 - 15 minutes of driving for the symptoms to show.

Any feedback would be greatly appreciated.

Cheers,
Rob
 

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I had a very similar problem with my car. It would only happen after sitting for the weekend. So the car would be perfect all week, except Monday morning where it would be fine whilst cold, then get really choppy (as in, I had to really nurse the throttle up to speed) after a few minutes of coming up to temp, all would go back to normal for the rest of the week. Drove me absolutely mad!

The good news (for me) is that my car no longer does it. It's strange, but I can't actually remember when it stopped doing it. The unfortunate news is that I can't pin-point exactly what fixed it either.

I can tell you that I haven't done or replaced anything major repair wise so that should be good news for you and your wallet.

I think I played around with the usual suspects. Ignition and fuel

Ignition wise:
I replaced all the plugs
I cleaned all the plug leads and made sure there was no corrosion on any of the contacts. I think I even put some dielectric grease on the boots to keep out moisture (just in case) (my leads were only 2 years old at the time so i didn't check them for general condition - but that is a good idea as well)

Fuel wise:
cleaned injectors
replaced fuel filter

As I write this, I am thinking that it was the electrical stuff which made the difference. plugs and leads. To me it felt like the car had a weak/no spark because if I was really, really gentle on the throttle you couldn't even notice the problem and it would rev cleanly (but slowly) to wherever I wanted.

The whole thing was very puzzling to me as It was a pretty fresh rebuild with all new MAF and other sensors so it *had* to be something simple.

I reckon check out your plugs and leads!
 

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Discussion Starter · #4 ·
Thank you vey much for the tip. I will give that a shot. I still find it strange that the problem does not occur immediately but after 10 minutes or so but hey whatever works.

Cheers,
Rob
 

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Tony's call for the engine coolant temp sensor which reports to the DME is an excellent call. The reason behind this call is that the computer decides how much fuel to deliver based on several factors, including the engine temperature. Therefore, if your coolant temp sensor is reporting,say, freezing temps, the engine would likely run just fine until the engine reached operating temperatures - at which point the fuel/air mixtures would be very wrong.

Of course, since you say this only happens when you haven't driven the car for a couple of days, it's quite possible that you've got a loose, or slightly corroded connection at that same coolant temp sensor, or at the intake air temp sensor.

As Pete suggests, there's also a likelihood of ignition issues, and if you haven't changed the distributor rotor and cap in a while, I'd put those items high on the list, along with sparkplugs.

Note that you have two coolant temp sensors: one reports to the gauge, the other reports to the DME. As I recall, the blue plug reports to the gauge, the brown to the DME, but it's easy to check this, by unplugging the blue one with the engine a bit warm. If the gauge reads nothing, then, the other plug reports to the DME.
 
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Discussion Starter · #8 ·
Tony's call for the engine coolant temp sensor which reports to the DME is an excellent call. The reason behind this call is that the computer decides how much fuel to deliver based on several factors, including the engine temperature. Therefore, if your coolant temp sensor is reporting,say, freezing temps, the engine would likely run just fine until the engine reached operating temperatures - at which point the fuel/air mixtures would be very wrong.

Of course, since you say this only happens when you haven't driven the car for a couple of days, it's quite possible that you've got a loose, or slightly corroded connection at that same coolant temp sensor, or at the intake air temp sensor.

As Pete suggests, there's also a likelihood of ignition issues, and if you haven't changed the distributor rotor and cap in a while, I'd put those items high on the list, along with sparkplugs.

Note that you have two coolant temp sensors: one reports to the gauge, the other reports to the DME. As I recall, the blue plug reports to the gauge, the brown to the DME, but it's easy to check this, by unplugging the blue one with the engine a bit warm. If the gauge reads nothing, then, the other plug reports to the DME.

Great, thanks for the explanation ,makes a lot of sense. I will be on my way to the dealer tomorrow to get that part. Hopefully that's the end of it.
 

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Discussion Starter · #9 ·
Might be leading injector

So went to the dealership today and they believe that it might be leaking fuel injector, especially since the problem happens while the car is sitting in the garage for a long time.

Does this sound right to anyone or are they out there trying to rob me?

Cheers,
Rob
 

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This is wrong. It's wrong, because a leaking injector would cause the issue immediately upon start up, from the overrich cylinder. Your issue happens when the car's in closed loop operation, and warmed up, which means that it's a sensor problem, most likely, and absolutely NOT an injector leaking.

I am never one to bad-mouth the dealership - but you should be aware that they are really not usually going to be the best place for you to get advice about your car -- because your car is outside of their area of expertise, by about 15 years. If there's an "old guy", (like me?) at your dealership, then he may be perfect for your needs. Otherwise, what you want is a top-of-the-line BMW specialist independent, and they should have an old BMW DIS (GT1) computer, or a modern BMW ISTA / ICOM computer, or Autologic with BMW software, preferably, because you can actually see coolant temp, etc, as the computer sees it. .

Now, if you are in a remote area of Canada, with no access to top-of-the-line BMW indy shops, then stay at the dealership, and ask for the tech who's been working on BMWs for the longest time.

It wouldn't hurt to go outside, find the sensor on the front of the thermostat housing (right front of the engine), gently pull of the plug (squeeze the metal part), and clean off the terminals with a fingernail file or sandpaper, or electrical contact cleaner from an auto parts store. Be very gentle, you're just cleaning off corrosion.

EDIT: Oh; they're NOT trying to rob you; but whoever said that didn't have all the information; he was likely told that it happened after the car was parked, but not told it was after the car warmed up.)
 

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Discussion Starter · #11 ·
This is wrong. It's wrong, because a leaking injector would cause the issue immediately upon start up, from the overrich cylinder. Your issue happens when the car's in closed loop operation, and warmed up, which means that it's a sensor problem, most likely, and absolutely NOT an injector leaking.

I am never one to bad-mouth the dealership - but you should be aware that they are really not usually going to be the best place for you to get advice about your car -- because your car is outside of their area of expertise, by about 15 years. If there's an "old guy", (like me?) at your dealership, then he may be perfect for your needs. Otherwise, what you want is a top-of-the-line BMW specialist independent, and they should have an old BMW DIS (GT1) computer, or a modern BMW ISTA / ICOM computer, or Autologic with BMW software, preferably, because you can actually see coolant temp, etc, as the computer sees it. .

Now, if you are in a remote area of Canada, with no access to top-of-the-line BMW indy shops, then stay at the dealership, and ask for the tech who's been working on BMWs for the longest time.

It wouldn't hurt to go outside, find the sensor on the front of the thermostat housing (right front of the engine), gently pull of the plug (squeeze the metal part), and clean off the terminals with a fingernail file or sandpaper, or electrical contact cleaner from an auto parts store. Be very gentle, you're just cleaning off corrosion.

EDIT: Oh; they're NOT trying to rob you; but whoever said that didn't have all the information; he was likely told that it happened after the car was parked, but not told it was after the car warmed up.)
Thank you for the explanation. I totally share your sentiments about getting a more experienced guy to look at it and they have one with 30 years of experience which I booked to see tomorrow.

I am not questioning your judgement but I had a few follow up questions to understand the problem better since I know far to less than I should to be owning this car:

Is it possible that the injector leak is ever so mild , so that the problem won't happen on everyday start up but only when the car has been sitting there for a while causing the accumulation of enough fuel to mess up the system?

And if it is indeed a sensor problem, why wouldn't it occur everyday when the car reaches running temperature but only after the car has been sitting for a few days?

Again, I am asking these so that I can intelligently question the dealership's assessment of the situation.

Thanks in advance for any additional feedback you might have.

Rob
 

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Hi Rob,

By all means, you are always welcome to question me, and my judgement. I have been wrong, many, many times....and I'm not done. ;)

The injector leaking would cause fuel to pool in the cylinder, when the engine is shut off, and as the residual pressure pushes the fuel out of the easiest opening. A leaking injector usually manifests as a difficult start, a cloud of black smoke, and a misfire for the first several seconds, until the excess fuel is blown out the exhaust. After that point, you might possibly have one cylinder misfiring badly at all low rpms, or no symptoms at all until the next start. Furthermore, a leaking injector would easily dump all the fuel pressure (and the fuel in the rail) within a few hours, not a few days.

The correlation between a several-day disuse, and your poor running ten to fifteen minutes later, really just "feels" like a temp sensor issue, or an an electrical resistance issue to me. Certainly, if your fuel filter is old, you should go ahead and change that, because it's a maintenance item anyway....but I don't see a correlation between fuel delivery and the particulars of this failure.

Certain electrical connections are subject to corrosion and excess resistance, which might just be linkable to sitting a few days. I'm not there to witness the symptoms, which might just lead me to an instinctive potential diagnosis. And that's why I think that your asking for the 30-year tech to diagnose the issue is a truly great idea.

Um. how old is your oxygen sensor? That's a maintenance item also, and a very likely culprit. I'm not one of those techs who "shotguns" parts at a car, but I'm absolutely in favor of throwing parts which are (a) overdue maintenance items, (b) inexpensive and quite likely related. (That temp sensor is about twenty dollars, as I recall....compare that to an hour's diagnostic time)

O2 sensor, spark plugs, cap, rotor, fuel filter, and the coolant temp sensor all fall into one or both of those categories. In the last 2 years, my car has had all of those except the temp sensor, just because. (And if you look at some of the pics of my car, you'll see I'm not an indulgent parent) ;)

This is just my 2 cents; I believe you'll find that the 30 year technician will be of great help.
 

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Discussion Starter · #13 ·
Hi Rob,

By all means, you are always welcome to question me, and my judgement. I have been wrong, many, many times....and I'm not done. ;)

The injector leaking would cause fuel to pool in the cylinder, when the engine is shut off, and as the residual pressure pushes the fuel out of the easiest opening. A leaking injector usually manifests as a difficult start, a cloud of black smoke, and a misfire for the first several seconds, until the excess fuel is blown out the exhaust. After that point, you might possibly have one cylinder misfiring badly at all low rpms, or no symptoms at all until the next start. Furthermore, a leaking injector would easily dump all the fuel pressure (and the fuel in the rail) within a few hours, not a few days.

The correlation between a several-day disuse, and your poor running ten to fifteen minutes later, really just "feels" like a temp sensor issue, or an an electrical resistance issue to me. Certainly, if your fuel filter is old, you should go ahead and change that, because it's a maintenance item anyway....but I don't see a correlation between fuel delivery and the particulars of this failure.

Certain electrical connections are subject to corrosion and excess resistance, which might just be linkable to sitting a few days. I'm not there to witness the symptoms, which might just lead me to an instinctive potential diagnosis. And that's why I think that your asking for the 30-year tech to diagnose the issue is a truly great idea.

Um. how old is your oxygen sensor? That's a maintenance item also, and a very likely culprit. I'm not one of those techs who "shotguns" parts at a car, but I'm absolutely in favor of throwing parts which are (a) overdue maintenance items, (b) inexpensive and quite likely related. (That temp sensor is about twenty dollars, as I recall....compare that to an hour's diagnostic time)

O2 sensor, spark plugs, cap, rotor, fuel filter, and the coolant temp sensor all fall into one or both of those categories. In the last 2 years, my car has had all of those except the temp sensor, just because. (And if you look at some of the pics of my car, you'll see I'm not an indulgent parent) ;)

This is just my 2 cents; I believe you'll find that the 30 year technician will be of great help.
Thanks a bunch Chris. That is great info. I can know throw some of these theories at them so that at least they get the perception that I know a few things :).

I will keep you guys posted as to what the technician recommends tomorrow.

Cheers,
Rob
 

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What was the results of this issue? I have a very similar issue with my E28 M5 now, and I think the coolant temp sensor is the issue.
 

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I am having similar symptoms as the OP and found this to be a very informative thread.

Does any have a quick picture relative to the location of the ECU temp sensor for the s38 b36 engine. I picked up my e34 m5 a couple of months ago (158k miles) and am diligently working through the maintenance issues (having already changed the plugs, cap, rotor and fuel filter). The ECU temp sensor sounds like a good one to add to the list.
 

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Please allow me to do one better for you. On the basis that, "If you give a man a fish", vs. "If you teach a man to fish". But Cliff notes: it's on the front of the thermostat housing, "inlet pipe".

First, click on this link to your wiring diagrams (I have chosen a '91):
http://wedophones.com/Manuals/BMW/1991 BMW 525i - 535i - M5 Electrical Troubleshooting Manual.pdf

Go ahead and download and save it, you'll want it in future, and this site is VERY safe and well respected.

Find the little symbols at the top of the dark area, click on"Toggle sidebar". More little symbols will appear; click on "Show document outline". Now you'll see a column on the left, scroll down to 1210.4 S38 (Click on it)

You'll be delivered to the "block diagram", which is an overview of all the stuff connected to your DME. You'll see, in the lower left, the engine coolant temp sensor.

You'll see several numbers associated with this: 1210.4-06 (This is the page number), and B6236 (This is the reference number for that part)

(Please note that the BMW page numbers are very different from the adobe page numbers, you are presently on adobe page 108, BMW page 1210.4

Now click or scroll forward 7 pages to adobe page 115, BMW page 1210.4-06; you will see the sensor, with it's wire colors: brown-red....and the ground wire will be brown, though unlabeled.

Your component number is B6236

Go to "Component Location Chart" in the left-side sidebar. Click on 7000.0

Look up B6236; you'll find "RH side, coolant inlet, pg 7100.00-12-3"

Back to outline, Left side, click on 7100, Component Location Views.

Scroll forward twelve pages, to 7100.0-12.

Look at view #3

Sensor is at the front of the thermostat housing, though the picture is dark and old.

All the very best!
Chris
 

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Chris -- Thank you for the great resource and particularly for taking the time to provide such a detailed walk through. I very much want to learn all I can about my car (which is an early '91 (BK05058)) and these discussions make me feel fortunate to be part of the community. Good luck with resolving your m5 situation. Regards, Jedd
 

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My car had a very similar sounding issue when I purchased it last year. Car would run like a top if driven every day, but if it sat for more than two days, I'd have the same running issue as the OP about 10 minutes into my drive. It'd clear up eventually and be fine. The previous owner spent a decent amount trying to remedy it, but to no avail. He replaced the following; coolant temp sensor, o2 sensor, fuel pump and filter, and MAF sensor. I got it home, popped the distributor cap off and quickly realized what my culprit likely was. Order a new cap, rotor, and plugs, installed them, and haven't had an issue since! From what I'm told, the distributor caps develop condensation in them and it causes the car to have weak spark as it burns the condensation off. Whether that's accurate or not, I have no idea, but it sounded plausible to me!

Jason
 

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found this thread before starting a new one on the same topic.

was making the short drive to work yesterday. Everything started out normally, then at first intersection - idle is up around 1700RPM. Second intersection and idle is up to 2K. Third intersection and the engine is rough and idle drops below normal RPM and dies. Cranks but will not start. Call for a tow truck. 30 minutes later, truck arrives, the car starts and CEL is on. Get the car home, and find a code for the coolant temp sensor.

Go to RealOEM and find P/N: 13-62-1-401-945 listed price: 70 bucks. Go to Autohaus AZ and they claim I need P/N: 13-62-1-284-397 and want 7 bucks.

Which sensor is the correct part number ? are they interchangeable ?
 

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They should be interchangeable part numbers.

this is Bosch standard sensor and the Bosch number is 0 280 130 026. see if any of their cross references show that number to be sure.
 
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