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Rough idle and misfire on cold starts.

4K views 16 replies 7 participants last post by  SinCitySpeed 
#1 ·
Hi guys, the past couple days when I let my car sit overnight or I get out of work from my eight hour shift I start the car the RPMs fluctuate between 1300 RPMs and idle and they keep going up and down for about a minute until it’s smooth out I will get increased admissions in limp mode. As soon as I shut the car off and start it back up all seems fine and then can drive it all day with no issues at all it seems to me when the car sits it does this.

I was thinking it could be an ionic control module because when I was monitoring the injectors during the cold start one through five had no timing, whereas cylinder six through 10 had injection timing. I provided two pictures showing the cold start with a misfires and after I shut it off turn it back on the injection timing seems back to normal.
 

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#2 ·
I found this on a website
“On the S85 engine the spark plugs act as a sensor by detecting the ionic resistance during combustion. The ionic current control unit detects this resistance and "talks" to the DME to adjust fueling and timing to optimize performance. A failed ionic current control unit can cause a limp mode condition or a constant misfire in a specific cylinder. In order to determine the cause of the misfire a diagnosis must be performed first. The most common way to identify the issue is related to the ionic current control module is to swap the units from each cylinder bank and see if the misfire issue follows the control module vs staying in the same cylinder.”
I switched bank 1 and bank 2 ionic sensors to see if the problem follows it to the opposite side I will wait for a cold start and let you know the details.
 
#5 ·
To monitor is different than to test.
To monitor:
you go to DME>Status>Analog>I/O 1 then you scroll down with down arrow on your keyboard to the end on the left "Kraftstoffdruck [bar]" after cold start and short drive any thing over 3.1 or les than 2.9 you have fuel pressure issue.

To test:
DME>F7 System>F5 Kraftstoffdruckregelung, don't forget to start the engine press the brake before you start the test.
 
#6 · (Edited)
Ok so I started the car after work and it was idling up and down about five seconds later it through a check engine light and went into limp mode the RPM slowly started to steady out one thing I noticed when I started the car as all the injectors had timing on the scanner when I was monitoring them. when the check engine light came on I lost injection timing to the passenger side cylinders because limp mode cut off the injectors. Out of curiosity I opened the filler cap for the oil and smelled it. I do smell some gasoline in the oil. The car is getting parked until the oil is changed and I figure out what’s going on. Leaking injectors? Im wondering is that why when the car sits it runs rough cause all the pressure leaked down?
 
#7 ·
I had a cylinder shutdown in mine one time and that one cylinder had the lowest reading. Cut the story short, I dropped some oil into that cylinder and then manually turned the crank and couple of times to get some oil on the cylinder walls. The reading came back up to normal like the rest. So it might be some type of fuel leak into the cylinder washing away that oil film off the walls causing the pressure to drop.
 
#8 ·
I did not do any pressure testing yet, I’m not going to start the car again until the oil is changed. I have a new set of injectors on the way. Is it possible for gasoline to get in the oil by the injector leaking over the course of a couple hours and seeping down through the piston rings into the pan? I believe that is what’s going on with me also I believe that’s why I’m getting rough cold starts and misfires on cold starts. As I stated before if I start the car let it run for like 30 seconds shut it off and start it back on it seams like it runs great and it will be fine the rest of the day as long as I don’t let it sit to long. it’s when I let it sit over night or while I’m at work the car gives me issues. Did you wind up changing your injectors?
 
#11 ·
The throttle actuator gears have already been replaced I did that last summer. When the car is running and driving it seems fine when I started up it misfires for a few minutes and then clears up. when I do a cold start I get a multiple cylinder misfire and it’s running extremely rough.
 
#12 ·
So I dropped the car off at the dealer they did some testing on the car and they recommended that I replace the venose solenoids. I talked to the technician he said everything that they did for testing checked out and came back fine other than a vanos Solenoid test, the solenoid failed a test or were below par. What do you guys recommend that I do? Should I try taking the solenoids out and cleaning them I heard you can clean them with compressed air and carburetor cleaner or should I just replace all four of them? If replacing is the next option where did you guys find the best prices for the solenoids?
 

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#14 ·
In post #22 I suggested to do fuel pressure test first, then you may bleed the Vanos system 2 or 3 times and test. Did the dealer bleed the Vanos. Have a look at the o2 sensor>Analog>I/O 3 also. I already noticed that there is a little deviation in cam position but I don't think that would cause a whole bank shut down, deviation present in both banks by the way. Many M5 are running fine with Vanos solenoids "below the set value", must define "set Value" even if quality value same result doesn't cause this.
Now dealer says "fault in 1-10 cylinders" not only in bank 1 as you said, this also increase the possibility of fuel delivery issue, fuel pressure test and consequent action is recommended at first start.
 
#15 ·
It's doubtful that the vanos could cause this type of problem. I think they are out at low RPM, in at Mid and out at High rpm. I'm sure they just ran a test and picked that as a place to start.

You said you did the TA gears so the air boxes were off? Double check all ten boots and make sure they are seated, both of my cars had loose or folded over boots. A smoke test would reveal and vacuum leaks which will cause cold start problems on any BMW.

If you are going to address the vanos just replace them. I think the issue with the test is an electrical one not mechanical.
 
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