Questions and Answers
Jetta Idle Hunting
Q. Hi, My problem is that when I start the engine and it is already warmed up, the idle goes up and down 4 to 5 times from 700 RPM to 1200 RPM before suddenly jumping to 2,000 RPM and then coming back very slowly to the normal idling speed which is 900 RPM.
Now, I have been told that the cause of this might be the O2 sensor or any other electrical part but that it would be difficult to pin point the problem until the part completely breaks. Could you please give me your opinion on what might be causing this problem?
1988 VW Jetta GL
1.8 liter 8 valves
Automatic
190,000 kms (118,000 miles)
Fuel Injection
No ABS
P/S- Yes, A/C- Yes, Cruise control- No
Rack & pinion steeringThank You,
KostaA. If the problem is constant and can be duplicated, I don't see why it can not be diagnosed at this point. VW had a problem with a sticking Idle Stabilizer Valve (ISV). If that is the problem then is will be corrected by installing a new ISV, P/N 037 906 457D.
Another possibility could be the O2 Sensor. Idle hunting is an indication of a properly functioning idle air control system trying to compensate for varying fuel/air mixtures.
Proper fuel/air mixture is required at all phases of operation. The Idle Air Control (IAC) Valve attempts to compensate for a low RPM by opening wider, increasing the air flow and in turn increasing the fuel injection time. When the mixture burns completely, the RPM will increase and the IAC will close. Idle hunting is due to the rapid opening and closing of the valve. So a careful check of all the engine operating systems needs to be done to insure they are working properly.
Additional Information provided courtesy of ALLDATA
