Here goes,
I own a 91 Passat 2.0Ltr which has an idling problem.
When the throttle is blipped it often drops to 300 RPM approx and sometimes stalls. If the car is left to tick over it is very erratic after several minutes.
When driving and the accelerator is lifted, at about 30 - 40 MPH and 1500 RPM approx the car becomes very jerky but is fine if the throttle is depressed and cruising along at a decent speed (provided that the revs are above 1500 - 2000 RPM approx).
Sometimes the throttle gives the impression that it is stuck open as the car surges forwards as if there is a demand from the pedal.
All of the problems appear to be on the very first part of the accelarator eg 1/2" to 3/4" of accelarator pedal depressed.
The car has been in the garage twice now (diagnostics) for which they have replaced the throttle potentiometer, distributor cap, plugs and fuel filter. They did comment that the CO2 pot has no adjustment and that the coolant temperature sensors were not working correctly but stated that it was not worth replacing these until the problem was diagnosed.
I have cleaned all of the rubber hoses and breather pipes and cleaned the carb butterfly with carb cleaner along with cleaning the 'Idle Stabilisation Valve'.
In attempting to fault find I have used a donar car and swapped over the top half of the air filter assy which includes the Air Mass Volume Sensor and the CO2 sensor, then I tried the coil assembly followed by the Idle Stabilisation Valve but not all at the same time with still no luck.
Since cleaning the revs are much higher.
Please....please....help as I don't want to scrap her as she looks nice and is worth keeping but I don't know what to try next.
Anyone out there who can help with advice?