540ia weird stumble / miss problem

[dreiko]

Hello everybody, I have a 1994 540ia and sometimes it will act like it is missing, but sometimes it will not. It has this stumble that is really annoying and can be felt at all low rpms, and will shake the car until about 3-3500 rpms where it finally smooths out. I have put new plugs into it, ran a little better, but still does it. The car just started to do this, just wondering if anybody experience this before? The part that confuses me is that it will run good and smooth sometimes, but then will do this? Any help appreciated!

[skylinergtr]

coil packs, maf, o2 sensors, pcv plate, vacuum leak. All of those and probably more than contribute to what your experiences. Do you get a check engine light when this miss happens. If so you need to get the code by doing a stomptest or using a scan tool. Best of luck.

[Sixdown]

I had the same issue and it ended up being the valve cover gaskets and an unplugged TPS. Did you see any oil in the spark plug holes when you changed them as that could mean leaking gaskets and possible vacuum issues? That could cause obvious misfire.

[dreiko]

I did a stomp test and there is a 1222 oxygen sensor code, but the check engine light never comes on, so I don't know if its an old code or not. Did not see any oil on the plugs when changing them. I am going to test the coils tomorrow, but does it make sense that a coil would work fine and not work every once in awhile? I just bought the car last month, so I don't know whats all been done to it. I can't see any vaccum leaks, or hear any...is there any "problem" areas in the vacuum system?

[skylinergtr]

if its missing the engine light will only come on when the car is studdering. Also a o2 sensor can make the car run like crap on these cars when they are fully warmed up. It happened to me. Changed both of them and it worked great again.

[dreiko]

When the car is stumbling the check engine light never comes on. This is what has me confused. Should I reset the check engine light? Is there any way to do this other than disconnecting the battery?

[skylinergtr]

i dont know if reseting the light will help. I have never reset it from disconnecting the battery. I always use a scan tool to check my codes and reset them. Is the car really bad to drive? Probably as it gets worse you will get another code and know what is faulty in the car. I dont want to tell you to replace something if its not going to help.

[dreiko]

I just test drove the car again, and once noticed that the last couple of times I drove it it has been only doing it after driving it for about 2 mins, which is leading me more twards the 1222 oxygen sensor. The check engine light never comes on when it is doing this, but I don't know if its actually missing, it seems more like a studder...I too would think that a miss would show up as a missfire and trigger the check engine light.

[skylinergtr]

does the car misfire when it idles? if it does try checking the coils by unpluging each one of them and detecting which one does not make a difference with the idle when its unpluged. I did this and found 2 of my coils to be weak. I then ordered a new set of bavauto performance coils and the car runs like a champ.

[dreiko]

Thanks for the advise, i read in Bentley that you can do a ohm test on the coils too, but yeah it does stumble when its idling when its doing it. I'll give that a try in the morning and see what I can find out. Thanks again for your help!

[skylinergtr]

No problem. I hope you find the problem soon and resolve it at minimal cost. If you find that one of your coils is defective make sure to mark it with a permanent marker or something. I helps you remember which one is the bad one. I know i've had to go back and check which was was doing it again... Also I have all my original coils still in my garage all nicely packed. I was looking at them today and i now know which ones are defective. Just incase i need one or i decide to sell them or something. Good luck!

[napuli]

I am also the new owner of a 540i auto, and I am experiencing simmilar problems. Not bad enough to call a tow truck but bad enough to know that there is something wrong. My code is 1213 which I think it is pretty much like the code you are getting. All I can tell you is that it has been getting much worse with the colder weather. In fact, in cold mornings it feels like the car is going to dye until the engine warms up. Just recently I nearly had a panic attack when the car started smoking like crazy. My CEL has been on and off several times and its getting worse -more frequent. I read as much as I could find in this forum regarding this problem. There are many good posts although they are somewhat hard to shearch. If anything, it sounds like rough idle that gets worse with colder weather is usually a good indication that the problem is due to a vacuum leak. In any case, I actually had a shop do a smoke test to find vacuum leaks. I don't really know how well that worked. They said they found and fixed a small leak somewhere in the intake manifold (I think PCV plate) and some oil in the plugs. Unfortunately, fixing the small leak fixed nothing. My current plan is to do a complete reseal of the intake manifold (including the PCV plate) before I try anything else. Who knows, maybe I will get lucky like others who found big gaping holes in their engines. Let me know how it goes for you.