Irregular idling

[Hans Mathias]

I have a 1998 Z3 2.8 coupe. When I changed gear and released the throttle, the revs would stay up where they were for a while, and when they did fall, it was all of a sudden with a bit of a 'jerk'. The revs sometimes climbed up by themselves when I was sitting in traffic. I was told that it was a faulty potentiometer. I changed it, but the error was still there. My mechanic took it to the electronic test, but found no errors. But he did reset the car's computer, and ever since it has been fine. So I could have saved installing a new potentiometer.

 

[Aceman]

Hi Hans and welcome to the forum.

This is not such an uncommon problem and is probably due to a split intake hose. If you check the rubber corrogated intake hose just after the airflow sensor where it bends 90 degrees into the throttle body there is a smaller pipe that branches off to the idle control valve which is prone to splitting. This allows extra unmetered air to enter the engine causing it to run lean and exhibit the symptons you are describing plus it would not show up on a diagnostic test. A replacement hose is not very expensive at around 15-20 euros and easily replaced. Whilst you have the intake hose off also check some of the other smaller pipes underneath the intake manifold as they are also prone to splitting causing similar problems.

Hope the above helps, now where are the pictures of your car as it is customary on here for people to post a pic of their Z as we all like a good picture.

 

[Hans Mathias]

Hi Aceman. After the resetting of the computer, the problem is gone. May be it was a coincidence. If so, I might have use of your recommendation. Thank you. And here is my car. 1998 Coupe, 2.8, 118.000 k (73.000 Miles). I have had the car for two months only. I have replaced the AC switch group, the light switch in the ceiling, a broken wire to the rare windshield wiper, fixed some scratches. The remote sometimes works on the left door. I have tried to spray some lub (CRC) into the door, but don't know if it helped. The other locks are fine. Greetings from Norway where we pay 3 times the car value in tax for a decent car with an over average motor (200 hp).

 

[Mint]

Hi Hans, to the forum from me also. You've got a good looking Coupe there

 

[hard top]

Welcome from me too.......