Anonymous asked in Cars & TransportationCar MakesBMW · 7 years ago

E34 540i bad cold idle?

This just started a few months ago, when I start the car in the morning (cold) the idle rocks the car side to side and the RPM will drop to 450 or so for about 15 seconds then come back up to normal. Also during the winter last year/ early this year it was hard to get the car to start when it was just starting up in the morning. However when the car is just past the cold mark on the temp gauge it starts and runs just fine. Also I notice I get a vibration at times when the car is warmed up and in drive stopped at traffic lights like a massage chair, feels like the whole car vibrates (idle @ 500-550), only when the A/C or main beams are on it goes away (idle 650-750) smooth as anything.

I have replaced the following:

Spark plugs,MAF,Intake temp sensor,Coolant temp sensor,O2 sensors,TPS,cleaned my ICV (dirty)

sea foamed intake system (more responsive throttle)

No smoke on startup or at anytime.

Have not tested for vacuum leaks.

Any help appreciated

1 Answer

  • 7 years ago
    Favorite Answer

    throw as many new parts as possible at it, don't stop where you've stopped, after several thousand dollars it will all be new and drive like a new car because new cars have all new parts. Or, take it somewhere to get a running scan and a stationary scan. The problem will reveal itself. But if you're on the replacement train, spray carburetor cleaner around the intake manifolds, if it increases in rpm you've got a leak. Also any trimming problems and O2 sensor faults can also be the result of a vacuum leak. The O2 sensors aren't bad, the just can't keep up with the added air to the cylinders as a result of the vacuum leak.

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