Rough idle

[ryansbmw]

Hey guys. Had this problem for a while and I want to get around to fixing it.

I have this rough idle problem. It only occurs on cold starts and only when I put the car in gear. (Staying in park, nothing seems to be wrong). The idle will be bouncing between 500 and 1000 rpm and if I try lightly pulling out of he parking spot, the car is lunging around. After 30 sec or so, it goes away and everything is fine. Warm starts and while cruising, no issues.

No steady or flashing check engine light. I scanned the whole car using Protool and no codes. Spark plugs and coils are new. A little while ago MHD was picking up some shadow codes related to fuel pressure-2BDE, 29F2, and 3164- but nothing ever became active. No shadow codes currently. I had the shop do a smoke test and take a look at the fuel tank ventilation valve and found no issues. Before starting the car, you can hear the fuel pump charging. Vacuum test was done on the boost solenoid and no problems there either

Any ideas what my problem could be? I know I need to do a little logging and see what the fuel pressures are at idle and when putting it into gear. Does anyone know what those values should be?

[ryansbmw]

Wasn’t able to start the car in cold start mode but driving around and doing some WOT, LPFP pressure stayed constant at 98.61psi. Rail pressure fluctuated anywhere from 1000 to 2600 psi. No signs of it suddenly dropping out. Accidentally deleted the file otherwise I would post the graph.

LPFP pressure reading a constant 98.61 seems a bit fishy. Our cars don’t have a low pressure sensor do they? I wonder how the car is calculating that

[ryansbmw]

I let the car sit 2 days. Plugged in Protool this morning and monitored the fuel pressure during start up. Pump pressure was 120 psi before starting the engine (Pump primed). At engine start and idle, pressure increased to ~1100psi and held. Once I put the car in drive and started to give a little gas to pull out of the parking spot, I started getting the bouncing idle and car started lunging. Fuel pressure increased towards 2000psi and was not cutting out or dropping. After 15 seconds and the lunging stopped, the pump continued to act normal. So it appears the the pumps aren’t the problem.

Any ideas where else to look?

[yco]

its pretty tough to make hypothetical calls but since everything is fine after cold start probably a faulty sensor that reads too much oxygen.. if i were you i d start by changing the fuel filter, then taking off and inspecting O2 sensor clean it and put it back, MAF sensor, inspecting vacuum lines and hoses again, doing a smoke test when the engine is cold yes you may need to leave the car for a day but still, checking cam position sensor, fuel injector problems, vacuum leak at intake manifold, temperature sensors can cause this as well or there can be some leakage on vanos.. unfortunately there might some work needed to find it..

[ryansbmw]

Yea I realize it’s gonna be some work. I figured I would get some sort of code to help narrow it down a bit. The interesting part is how it’s fine until I shift into drive. Cold start and idle in park is fine. I’m trying to think what sensor or part changes at the point I shift. Curious now if I shift to neutral or reverse if the same thing will happen. More testing to do!

With the MAF sensor, if I recall on some older models, you can unplug the sensor and see if the car drives better or worse. If it’s better, that’s a sign the sensor has gone bad. Is that still the case with the newer cars?

All the joys of having a BMW!

[ryansbmw]

Another update.

I’ve run 2 bottles of Techron fuel system cleaner thru the tank and no change.

Putting the car into reverse and giving it a tiny bit of gas will produce the same lunging effect. On two occasions the car has actually stalled out and shut down 2 times before I was able to pull far enough out of the spot.

Still no codes.

Next step will be try cleaning the MAF sensor.

[raedalwan]

Originally Posted by ryansbmw

Another update.

I’ve run 2 bottles of Techron fuel system cleaner thru the tank and no change.

Putting the car into reverse and giving it a tiny bit of gas will produce the same lunging effect. On two occasions the car has actually stalled out and shut down 2 times before I was able to pull far enough out of the spot.

Still no codes.

Next step will be try cleaning the MAF sensor.

did you figure out your issue? I was thinking if only happening while shifting to R or D it could be something related to torque convertor!

[ryansbmw]

Not yet.

I did notice that when letting it idle on cold starts, the rpms are bouncing a bit in the beginning before settling down sometimes. Other times it stays relatively steady but can feel the he engine stumbling a bit. It’s very slight tho. Maybe it’s the injectors? Maybe there is an air leak that somehow seals up once the engine is warm?

Gonna try cleaning the MAF sensor this week now that I’m home. Doubt it will do anything but it’s worth a shot.

I hope it’s not an issue related to the torque converter. I figured that would pop some codes, no? My e39 had a torque converter issue, which eventually took out the entire transmission, but I was able to pull codes for that.

[hennessy_r24]

Valvetronic motor stock open. Is locate in head under the valve cover. I have Being running with the same issue for the past 40k+ miles, will replace it next time the valve cover come off.for some reason.

[ryansbmw]

Originally Posted by hennessy_r24

Valvetronic motor stock open. Is locate in head under the valve cover. I have Being running with the same issue for the past 40k+ miles, will replace it next time the valve cover come off.for some reason.

Interesting. I’ll have to research that more! What led you to that conclusion on your car? Any codes?

Yesterday I started the car for the 1st time I a week. I let it idle in park and I could feel the car stuttering and it actually stalled out. Restarted it and all was fine. It’s getting rather annoying.

Edit: Just went out again to start the car and sure enough, it died while idling in park. Still no codes present.

[ryansbmw]

Started the car up this morning and the reduced power message popped up on the dash. Finally was able to pull a few codes.
2774- Air mass plausibility: air mass too high
2C58- Charging pressure control: switch off as consequence
2D55: variable camshaft timing control (VANOS), intake, cold start: not controllable

Message says driving is still possible but to visit a dealer to have it checked. Figures this happens while I’m in Cleveland and supposed to be driving back to NJ tomorrow. Am I risking damage to the engine if I attempt this drive?

[cloudybimmie]

I am having somewhat same issue, i replaced the valve cover gasket, valve cover, spark plugs and coils, put everything back together, now i have code 28A0 - (intake pipe absolute pressure, plausibility: Pressure too high) and 2BEA - (mixture Control: fuel air mixture too lean). so far i've changed the turbo\vacuum hoses, cleaned the MAF sensor. I did unplug the valvetronic motor and the car didn't throw the 28A0 code, but did throw the valvetronic unplugged short circuit code.

Any help would be greatly appreciated

[randrews15]

Have you looked for a vacuum leak? Previous BMW engines would do similar stalling problems when a vacuum leak developed but would throw a code to do so. I did work on my Mom's Mercedes as it was constantly throwing a too lean code for both banks. I ended up replacing all the vacuum lines after a smoke test was inconclusive. That ended up clearing the codes and restored drive ability. I suspect the leak was so minor that a smoke test couldn't find it but the sensors could.

[ryansbmw]

The shop smoke tested the engine earlier in the year but couldnt find anything.

Maybe now, if there is a leak, it’s gotten bad enough to be found. This is the 1st time I’ve had any codes or warnings pop up so I’m hoping when I bring it to the shop next week they can smoke test or function test the VANOS and boost solenoids to see if they are working properly. I cleared the codes and drove 6 hrs from Cleveland to New York without issue.

The fact that this only happens on the initial cold start leads me to believe it’s not a vacuum leak. If the engine stalls out, I can immediately start it back up and everything is fine.

[cloudybimmie]

Originally Posted by ryansbmw

The shop smoke tested the engine earlier in the year but couldnt find anything.

Maybe now, if there is a leak, it’s gotten bad enough to be found. This is the 1st time I’ve had any codes or warnings pop up so I’m hoping when I bring it to the shop next week they can smoke test or function test the VANOS and boost solenoids to see if they are working properly. I cleared the codes and drove 6 hrs from Cleveland to New York without issue.

The fact that this only happens on the initial cold start leads me to believe it’s not a vacuum leak. If the engine stalls out, I can immediately start it back up and everything is fine.

thanks for the reply, i found my issue, it was a bad valve cover that was causing this code.

[ryansbmw]

Last weekend, I cleaned the MAF sensor and replaced the TMAP sensor with a 3.5bar from the N20- no change.

So I dropped the car off at the shop on Monday afternoon to have this rough idle issue looked at a bit more and also fix a squealing belt and pulleys. Sure enough, they didnt witness the rough idle once in the 3 days they had the car. They checked for air leaks and nothing. No codes anywhere (not a surprise). Ill need to ask them if they did the VANOS and valvetronic motor test on ISTA or not when I pick up the car.

Is it possible the belts and pulley caused all of this? They said the belt was stretched and the pulleys had some play. It had been chirping when the engine was cold but would eventually go away. Would that be enough to cause this issue?

[Falen]

Originally Posted by cloudybimmie

thanks for the reply, i found my issue, it was a bad valve cover that was causing this code.

Hi, I have the same problem as you code 28A0. I would like to know how you came to the conclusion that it was the valve cover which was detective.

[asdf4fdsa]

Originally Posted by ryansbmw

Last weekend, I cleaned the MAF sensor and replaced the TMAP sensor with a 3.5bar from the N20- no change.

So I dropped the car off at the shop on Monday afternoon to have this rough idle issue looked at a bit more and also fix a squealing belt and pulleys. Sure enough, they didnt witness the rough idle once in the 3 days they had the car. They checked for air leaks and nothing. No codes anywhere (not a surprise). Ill need to ask them if they did the VANOS and valvetronic motor test on ISTA or not when I pick up the car.

Is it possible the belts and pulley caused all of this? They said the belt was stretched and the pulleys had some play. It had been chirping when the engine was cold but would eventually go away. Would that be enough to cause this issue?

I've got a similar erratic idle at start, but have never stalled out (yet?). I've been hunting for the last few months. I had a belt shred incident, but verified not much was ingested (by weight <40g's). I've replaced the front crank seal, changed belt, the 2 idlers, tensioner, and wire brushed all pulleys for gunk. I've verified all vacuum lines and locations for leaks, valve cover was replaced last year. To try, I still have 5 other injectors to replace, and maybe try the VANOS squirter to declog. Will need some more ideas as well.

Originally Posted by Falen

Hi, I have the same problem as you code 28A0. I would like to know how you came to the conclusion that it was the valve cover which was detective.

For 28A0, if you have verified all your vacuum lines and intake piping is free of leaks, smoke tested, etc, then last resort is to try the 15min idle workaround: https://static.nhtsa.gov/odi/tsbs/20...63029-9999.pdf

Basically, pull the Fuel Purge connector, idle for 15mins, replace and go driving for 15mins. It's unbelievable, but worked for me.