I'm fighting a high idle when warm

RickKlem · 11-30-2003, 01:38 PM

My idle run's up to 2100 after warmed up engine. I can get it to drop by using the clutch tip ( put car in gear, release clutch just a little , then press in clutch again) . I did a search on aav and decel valve and found alot of true facts and alot of crapola. I can remove the (small) vacuum line from the back of the decel valve and the idle will drop to normal. But the way this thing is piped through the aav , I'm not sure if it is the decel valve or it's covering up another problem ( bad aav).

I have read that you can remove both and the car will run just fine . The aav is a bear to get to , so I dont want to lower the motor and plug the aav, if the problem is the decel vavle.

Please, someone help me think straight.

This is a 80 3.0l cis car

Gordo2 · Gordo2's Garage

My '83 has the exact same problem. I haven't started to troubleshoot it yet, hope to get at it this winter.

Will follow your post, hope you figure it out. If you do, please let me know.

Thanks, Gordo

no substitute · 11-30-2003, 04:02 PM

Yeah, me too, although my idle is sometimes about normal. I'm wondering if this requires the famous knocking the pin project.

Vipergrün · 11-30-2003, 04:16 PM

Isn't *knocking the pin* done to the Warm Up Regulator? I have heard you can smash the decel valve down a bit and beat it into compliance. I leave my decel valve disconnected and plugged the vacuum hose.

-B

RickKlem · 12-01-2003, 08:09 AM

weekend bump

Gordo2 · Gordo2's Garage

When I get at it...

I plan to start by disconnecting my O2 sensor and driving it for a while to see what kind of impact it may have.

From there I will move into other areas (WUR...).

Have you tried disconnecting yours yet?

Gordo

Jcon · 12-02-2003, 03:02 PM

I know someone here has dealt with this. My car has the same problem. Even more odd though is at hot start up.

Engine at operating temp - idle at a nice 900RPM.

I shut it off to pump some gas - Get back in turn the key and it revs to 2100. Really freaks people out around me. I always get that look like what an A-hole reving his "porch".

Anybody have any ideas..CIS Gurus?

Jeff C

Jcon · 12-02-2003, 05:47 PM

Bump for the West Coast crowd

howiee · howiee's Garage

Did any of you figure out what is causing this? I have the same problem with my 83. Did unplugging the decelerator valve cure the problem and did it cause other problems to surface?

Any new ideas floating around?

Rondinone · 03-15-2004, 10:31 AM

My car idled at 1800 before the rebuild. During the teardown, I found that the woven breather hose had split at the engine end, resulting in a massive vacuum leak. I also replaced all six fuel injector o-rings. Other than that, I didn't do any real work on the CIS. Now the idle is a rock-steady 1050. I have no idea why as a vacuum leak usually decreases idle.

howiee · howiee's Garage

rondinone:
Did yours idle high only after it was warm? mine is fine until I shut it down and restart it warm. Then it idles up to 2500rpm. once I start driving it it calms down.

Anyone know if it could be the vacume advance on the distributor. Someone mentioned it to me but I don't understand how advancing the timing would increase the idle?

ruf-porsche · ruf-porsche's Garage

Quote:

Originally posted by SoCal911SC
Vacuum leak somewhere?

I second that opinion. The hoses and connections on these cars are getting pretty old, vacuum leak the most likely culprit.

SilverPoly · 03-15-2004, 01:46 PM

It may be a vacuum leak as has been suggested.

Though, I had a high idle problem when my car was warm also. It turned out to be the decel valve or auxillary air device as some would call it. Did you try adjusting it?

On top of the valve there is the threaded vacuum nipple and a locknut. Loosen the nut and you can screw the nipple in or out of the decel valve. By going in, you lower the amount of time the rpm holds. By screwing it out the hold time is longer and hold RPM is higher. Don't forget to re-tighten the locknut.

You can adjust how long the valve holds the engine at high RPM after deceleration. This fix worked for me.

Mookster · Mookster's Garage

Replace the small diameter vacuum lines (inside diameter 3mm).

My idle was running high and the original lines were toast. After replacing the vacuum lines the idle went from 1200 to a steady 1050rpm without any adjustments. The fabric colored vacuum lines are about $1.25 a foot, non-fabric lines are about $0.75 a foot at any autoparts store. You will need 12-15 feet if I recall.

Be cafefull removing the lines and knowing where they attach. I had a heck of a time finding the fitting on the back of the throttle body.

No guarantees it will solve your problem. I can say if the vacuum lines are the original hoses it cannot.

Good luck