Idle rises after car warms up

[Mike80911]

The issue : My car starts up perfectly, turn the key on then turn it to start fires right up idles at about 1400 then drops down to about 1000. Car runs great plenty of power steady idle. But after warming up for a while the idle then goes up to about 1700-1800 and stays there. Any ideas what could be going on? 1989 completely stock no mods at all.
Thanks

[908/930]

Here is something to try, follow the vac lines from the distributer and bypass the thermo valve, I do not remember if there is something on each line. If I remember correctly if this valve fails it can stop the distributer from retarding on boost, so go easy until you sort it out. And make sure your distributor adv / ret is working properly.

[Mike80911]

Thanks for the reply. How do I check the adv / ret to make sure they are functioning properly?

[908/930]

The only other thing I can think of would be that your auxiliary air regulator is not closing, try blocking the hose. Check this first.

[Mike80911]

Thanks I will try that

[Mike80911]

I took the AAR valve off and checked it using cold and heat and it is opening and closing. I put the valve back on the car and checked for power with the car running. I did not get power to the AAR with the car running at idle. Should the AAR be getting 12 volts at idle with the car running?

[Alan L]

Yes.
If that circuit is not live, the disc will not close - leading to a lean idle (and likely higher revs).
The power comes via the WUR circuit. Direct from the WUR. They share a common earth. You are not getting the 12V at the terminals on the plug?
You could try putting 12V over the pins in the socket (+/- orientation doesn't matter) on the AAR - the disc should close after about 5 min. (torch and mirror)
Alan

[Mike80911]

Just an update. Turns out 908/930 was correct both vacuum lines to the distributor were split so neither advance or retard were functioning. Thanks for all of the help

[alhilalsa]

good job

[908/930]

Nice when it is an easy fix. The distributer not retarding can be a real large problem in a short time.