*FIXED* Another M42 Rough Idle Problem
 

Hi there. I have a 1995 318ti M42 with 328,000km. The idle has never been perfect on this car but in the last few months it seems to have gotten worse to the point where it will almost stall when it is warm.

I've read as many forum posts as I can and tried testing/replacing many items to no avail. I turn to you folks for advice on what to check next. I am going to try and post a video to help show the symptoms.

The idle is rough right from a cold start, however it seems to get worse as it warms up. Once it is warm, it will drop to under 500 rpm and almost stall, then kick up to 1200 rpm to keep itself running, level off at 800 rpm for a second or 2 then start dropping and repeat.

If I hold the throttle steady in neutral under 2000 rpm I can feel the engine shudder. Above that it seems smooth I think. It seems to drive smooth otherwise however it feels like it is lacking power.

I have replaced/checked/cleaned the following:
- New Head Gasket (upper and lower timing chain cover gasket as well)
- New Spark plugs/wires
- New ICV
- New O2 Sensor
- New knock sensors
- New CPS
- New Coolant temp sensor
- Replaced the big vacuum hoses (ICV to and from, valve cover to CCV)
- Cleaned the MAF (as much as you can with the barn door style)
- Replaced check valve and grommet for brake booster
- Checked the 'spider' hoses going to the injectors.

I've tried disconnecting the line from the CCV to the valve cover at the valve cover and plugging the hose to test the CCV with no change. I've sprayed throttle body cleaner on every hose to try and hear a vacuum leak. I am hoping to try and set up some kind of smoke test to test again for vacuum leaks.

It does smell like it is running rich. Also, the engine/exhaust sound goes from a chug, chug, chug, to a bupada, bupada, bupada, then back to a chug, chug, chug (this is why I need to upload a video :wink:) Please let me know if there is more information that I can supply to help diagnose. Thanks! Chad

Videos
 

Here are 2 videos that I took this morning. One of the engine still cold and the other with the engine warmed up.

cold

https://www.youtube.com/watch?v=y2L0pAnT64M

warm

https://www.youtube.com/watch?v=HQtQN0Ng1f0

You sure you aren't working on my M42?

I also found the vacuum hoses to the injectors cracked.
I need to fill the tank to see if that makes a difference.

You think it could be a fuel pump?
I've been told to monitor fuel pressure. Waiting for the temps to warm up.

I haven't checked the fuel pressure so I will add that to the list. I don't think its the fuel pump as it seems to drive ok and smells more rich than anything.

I did check the injector tee and hoses and they all looked ok. The Orings on the injectors also looked ok.

I am definitely leaning towards a vacuum leak somewhere but I'm just not sure where else to look?

Still chasing this rough idle problem. I ordered some orings for my injectors just as something else to try, however I have sprayed everywhere with throttle body cleaner with no real noticeable change in idle.

I hooked up a vacuum gauge and I am fluctuating between 6-9 inHG at idle.

Here is a video I took tonight:

https://www.youtube.com/watch?v=9_gzXlLmrtM

Let me know if you guys think I should try anything else.

Thanks.

On a healthy engine with no vacuum leaks, the idle behaves rough, the same way as yours if you remove the oil fill cap on top of the valve cover. This replicates a big vacuum leak. Does your engine behave the same way?

We had the same problem before after replacing the valve cover gasket and spark plug round grommets due to oil filling up the spark plug holes.
Came to find out the valve cover gasket was not properly seated on the back side. Had to take the valve cover back out and reseat the gasket. The idle smoothened out after that.

Your oscillating idle is a big vacuum leak.

Thanks for the reply. Interesting point on the valve cover gasket. I will probably try that this weekend and update if it made a difference or not.

Tried the following the other night:

1. Re-seated the valve cover gasket.

2. Replaced injector O-rings

3. Replaced PCV

Any other ideas for vacuum leaks? I feel like I've sprayed throttle body cleaner all over the engine with no change in idle. So maybe the leak is somewhere underneath?

Any other ideas of what to check for vacuum leaks would be appreciated.

Thanks!

*FIXED* M42 Rough Idle
 

So this weekend I came up with a hypothesis. About a week after I bought the car, my dad and I tore the top end apart to replace the head gasket. I vividly remember hanging the cams/cam gears to the hood of the car using a wire coat hanger (for the record this last time I replaced the head gasket I zip tied the chain to the cam gears). The coat hanger slipped, but my dad and I both we confident at the time that we caught it with everything still in the correct position. Playing devils advocate I decided I should check the cam gears for alignment.

Turns out this was the problem as the passenger side cam gear (the one picked up by the cam position sensor) was off by 1 tooth. The camshafts were never moved, but the cam gear was off. So therefore the engine was mechanically aligned but the sensor was picking up the cam position incorrectly, thus firing the injectors and spark plugs at the wrong time. Every picture and forum I read about TDC and cam alignment showed 15 'rivets' inclusive between the two TDC arrows of the cam gears...mine had 16. Driving to work this morning was like driving a new car. Idle was silky smooth (for 330,000 km) and definitely more power and likely better mileage. Thanks to everyone who contributed ideas to help fix this problem.

Hi OP I'm a noobie… I'm having the same problem as yours … if you are still here can you tell me and show me pic about these… On your post you said about…

"...15 'rivets' inclusive between the two TDC arrows of the cam gears…"

please post up some diagram or pics of what you mean?…

kind regards…