Jdub303

Hey everybody,

1988 Audi 90 Quattro. I have been trying to find the cause of my idle issue for a couple months now, and I am now leaning towards it having to do with the PCV system. My car only has 80k on it and all vac lines and gaskets seem to be in very good condition. I've replaced plugs, wires, o2 sensor, knock sensor, air filter, fuel filter, coolant temp sensor, and thermostat and the prob still persists. When hot, it likes to rise to about 1800ish and stay there until I engage the transmission, and just jump around at other times. I've tried everything short of digging into the PCV system hence my suspicions. When having trouble with a PCV system, what is the usual culprit? a "full" carbon canister or the solenoid? My solenoid makes no noise at all now, while before it would start clicking at the precise time my idle would start to rise. I've been told the clicking is normal, but as it seemed to correlate to the idle issue I wonder if it is bad. Also, for what its worth, the IAC is clean as a whistle. Thoughts please! Also, where the heck can I get a new one it the consensus is a bad solenoid?

Thanks much.

Rusty Spokes

I would look for air leaks for sure..the boot and all the connector hoses. The 88 had CIS K jet injection and is sensitive to air leaks and needs to set it up correctly..you need to check the system and control pressures (if the CP regulator is not working correctly, you will get all kinds of problems) with the correct gauges. The sensor plate in the air flow meter should be checked too to be sure it is set at the correct height and is not binding too.

Rather than putting parts on the car..do find someone with the correct gauges and check your pressures. The tool is available on Amazon:https://www.amazon.com/CTA-Tools-342...ion+Tester#Ask

Jdub303

Hi Rusty,

Thanks for the reply. I'll go over the hoses and boots again to see if I missed something. What is the CP regulator? I have not come across this term before. The sensor plate seems to be adjusted correctly even if it appears to off center by a fraction of a hair. Any other thoughts would be very welcome!

Thanks again.

Rusty Spokes

Sorry..CP ..control pressure regulator..also called a "warm up regulator" it controls how much the sensor plate piston moves..when cold the sensor plate moves easily and with little resistance (rich)..once warm more resistance and very firm resistance (lean)..very important that the pressures are checked.

It looks like this:


The overall fuel mixture..rich or lean should be checked too with a CO machine..too rich or lean once the engine is warmed up will cause problems too. Mixture is adjustable with a small allen wrench.

Jdub303

Thanks Rusty,

I'll look into this. I went over all the lines again and they seem OK. Despite lacking in basic maintenance, this car is in exceptional shape and was obviously barely driven. All the parts I've replaced were just filed under the "needs to be done" category-the air filter was from 1992! Anyway, I'll report back with any new news. Thanks again.