740i - Rough Idle

[MICHAELC]

HELP!

I HAVE A `93 740i WITH A ROUGH IDLE, ENGINE RUNS GREAT ABOVE IDLE. I HAVE CHECKED ALL I KNOW TO CHECK AT THIS POINT WITHOUT THE HELP OF A SCANTOOL (i.e. VACUUM LEAKS ETC.) I HAVE ALSO CHANGED THE PCV CASE WHICH HELPED SOMEWHAT BUT STILL HAS NOTICEABLE ROUGH IDLE. I WOULD APPRECIATE ANY HELP WITH THIS MATTER

MICHAEL

[swedish]

I don't know if the scan would have showed this, but it sounds like an o2 sensor. Welcome aboard by the way.

[Carfixerdo]

With a rough running vehicle I think there are some things that you can look at. With a little investment in tools such as a vacuum gauge, ether spray, and spark plug tester you can probably rule out a number of items. A rough riding engine that smooths out is rarely an O2 sensor. This sounds more like a MAP or MAS sensor. Anyway I would begin with a vacuum gauge. Find a source of vacuum on the engine and hook the gauge up. A good running engine should read between 15-20 mmHg. If this is not a steady reading or is low then there is a leak somewhere. If this is fine then I would use the spark plug tester on each spark plug wire and look for a good spark. You will know when one is bad by seeing how the others are doing. This will help rule out a bad wire or coil. Vacuum leaks and bad wires, plugs and coils our the primary reasons for bad running engines. If these all look good then I would suspect a bad MAP or MAS sensor. I hope this helps.
P.S. I forgot to tell you why the ether spray. If the vacuum gauge is reading low then use the spray to spray the intake. If the engine picks up RPMS then you know that the leak is somewhere where you sprayed the ether.

[mculex]

where is the pcv thing you are talking about?,you know on most american cars they are easy to find but i can not seem to find it on my 93 740i.