E34 540i cold ambient air idle problem

Funfer · 02-07-2003, 07:03 AM

Maybe y'all can help with this one.

Situ: 1994 540i with alusil motor and car in excellent state of tune. During cold temperatures below 50 F the car at idle will have a rough idle. At temps above 50-60 F the car will run and idle perfectly. This occurs during engine warm up and at operating temps. The car will not die, but rather have lumpy idle at 450-500 rpm.

Corrective measures taken to fix: Replaced the following-Cyclonic valve, MAF, both O2 sensors, plugs, DME coolant temp sending unit, fuel pump and filters(Bad anyway), crank position sensor, intake manifold gaskets, intake return tube o-rings and Air filter. Cleaned ICV, and throttle body.

I have had this thing going through 2 winters now and can't find the solution. It is pre-OBDII so diagnosis is a bit more difficult. The last codes I had read were that it was too rich and could not lean mixture anymore. After replacing the engine coolant temp sensor(black connector) it did run a little better.

Hopefully between all of y'all there you can help me a bit. I know of several e34 M60 owners who have this same identical problem. Thanks a bunch!
John Paap

john-e-boy · 02-09-2003, 12:12 AM

I have the same problem on my 91 525i, I was told that it was the throttle position sensor, the way it was explained to me was that when the sensor goes bad the computer doesn't know where the throttle is and causes the car to run rough and the idle to vary.

It is the sensor on the side of the throttle body. I haven't got around to change mine yet so I don't know if that is it for sure but it is worth a shot.

John

Funfer · 02-10-2003, 05:11 PM

Thanks for the info, John. Replaced those too. One fot the throttle body an one for the ASC+T. Any other suggestions?

john-e-boy · 02-11-2003, 12:01 PM

I talked to a guy today about the problem and he seemed pretty informative, he heard my car run and said it was the "cold start sensor", He said it will give you problems in either of two ways, one the sensor just doesn't work and makes the gas mixture too lean or two it doesn't stop working until the car warms up which is the problem I have. It delivers too much fuel to the engine causing it to run rough which would explain why the exhaust has a rich smell to it.

It makes sence to me seeing that I only have this problem when it is cold out. Well the good news is that this might be our problem but the bad news is the price, Over here in Germany at the BMW dealer the cold air sensor was 180 euro or roughly $190.

Oh and the sensor on my car, M50 motor (24 valve), is right next to the throttle body drilled into the flat portion of the intake (i believe). The best thing to do is ask the guy at the parts counter exactly where it is, He can bring up the picture on the computer.

Hope it helps and let me know how you make out

John

Funfer · 02-11-2003, 12:22 PM

John,

Interesting. Next time you talk with your BMW Tech ask him where to find one on an M60 motor. I do have an air intake temperature sensor but I replaced it two weeks ago too. It didn't work either. It was located on the passenger side of the intake manifold up near cylinder #1. I bought it for about $41 here so it may not be the same part you are talking about. I live in Augusta, GA so the amount of expertise here is limited.....Can't find that much expertise on the web about this problem either.

Thanks for the pointer. John