Idle revving problem

[guru]

This behaviour started recently on my 82 SC. I would start the car for the first time during the day to warm it up. Idle is aroun 1000-1500 rpm. Around 10-15 mins in, the idle starts to drop and the engine revs it back and this repeats as if the engine (or ECU) is repeatedly blipping the throttle to prevent it from dying. Sometime the engine dies and sometimes it seems to correct itself and maintain a steady idle at aropund 1000 after maybe 20 mins.

This is not limited to idle but also happens when I drive the car every coupla times but only when I engage the clutch

Any pointers on what could cause this or where I shoudl be looking? Also, the weather has become warmer in Seattle, just fyi

[83_Silberpfeil]

Thanks for posting this issue. I experience this with my 83 SC as well. But, it only happens during warm-up (first drive of the day). It hasn't bothered me that much yet, that's why I haven't looked into it or posted the issue. But now that you posted, I'm all ears on possible culprits.

[MysticLlama]

Mine used to do that on occasion. I think when it was doing it a little it was just the fuel adjustment, when it started to be real bad I think my WUR was going. I never can remember if that's when it is too rich or too lean. Was quite a while ago, so I can't recall exactly. Possibly also flaky O2 sensor if you still have one.

Give John Walker a call, he can fix it. It's best to test it on the gas meter at least first before fiddling with stuff that could be fine.

FWIW, mine usually still has to be adjusted once in the spring and once in the fall to adjust to conditions.

[Joe Bob]

Do you have a decel valve?

[Bob Kontak]

Originally Posted by Joe Bob

Do you have a decel valve?

+1 - You can plug the hose from the decel valve to see if it is the culprit. If it is, then you can keep it plugged or search on how to squish the valve in the center and bump it back to within acceptable operating limits.

It's one of the two cadmium plated flying saucer parts on the passenger side of the engine compartment. It is the one closest to the rear bumper and has a small hose attached that you can pull off an plug with a nail/golf tee.

Edit: I had similar symptoms and unplugged the decel valve two years ago and it helped. However, once I found a decent size vacuum leak last year I reconnected the decel valve have had not had the symptom again.

[T77911S]

the mixture is too rich. most likely due to a bad warm up regulator (WUR) or maybe a bad frquency valve.
first, you need to have the pressures checked.