High idle

[efnfast]

Sometimes my idle gets stuck north of 2,000 rpm. It doesn't seem to be throttle related, as in the cable or plates.
The only way to get it to come back down is pull over, come to a complete stop and wait a bit. Less than a minute.
Thoughts?

[Young1]

Buy throttle body cleaner spray. Remove accordion. Spray clean all well. Especially the little plate. Remove aluminum cover over cable. Spray all the mechanism with spray. First idea is grime because you have a higher mileage car.

[efnfast]

I'll try that Steve, but it doesn't seem to be plate or cable related. If it was, I should be able to "tap" it down, or I could push in the clutch at speed and let it come down. It won't. The only way to get it to come down is bring the car to 0 mph. It feels like it's tune related.

[tccrab]

My '90 does something similar, but not as extreme.
Approaching a stop the idle is around 1400rpm, once stopped for a few seconds the idle drops to 800ish.
Ive always believed it was smog related and allowing the cats to stay hot on deceleration.

Crabs

[XfireZ51]

I had that issue some years ago. My TB is bored to 63mm. I ended up buying Marc?s ?helper spring?. After all these years the return spring loses some of its closing power. Haven?t had that issue since.

[efnfast]

It doesn't feel mechanical. I can coast down the highway with the clutch in for miles and the idle will never come down. Not until I come to a complete stop will it self correct.

[Young1]

Quote from service manual

Incorrect minimum idle speed may be caused by foreign material accumulation in the throttle, bore caulking, on the throttle valve, or on the throttle shaft.

Also a little research indicates to remove the IAC idle air control on the passenger side of the Plenum. It?s round with two small flanges, remove it, clean it and clean the passages in the plenum.

Hope this helps for your high miler

[Mystic ZR-1]

Originally Posted by Young1

Quote from service manual

Incorrect minimum idle speed may be caused by foreign material accumulation in the throttle, bore caulking, on the throttle valve, or on the throttle shaft.

Also a little research indicates to remove the IAC idle air control on the passenger side of the Plenum. It?s round with two small flanges, remove it, clean it and clean the passages in the plenum.

Hope this helps for your high miler

I do that every couple of driving seasons, never had an idling problem.
You'd be suprised how much stuff is on it.

[efnfast]

Originally Posted by Young1

Quote from service manual

Incorrect minimum idle speed may be caused by foreign material accumulation in the throttle, bore caulking, on the throttle valve, or on the throttle shaft.

Also a little research indicates to remove the IAC idle air control on the passenger side of the Plenum. It?s round with two small flanges, remove it, clean it and clean the passages in the plenum.

Hope this helps for your high miler

This is what my mechanic suggested and it sounds perfect. I'll get some throttle body cleaner before I take it apart.

[efnfast]

Thanks Yun, I think you fixed it, no problems coming home. I'll get some cleaner and pull the IAC again and give it another shot.