I took a long trip -- 2500 miles -- in our 1980 SC. During the trip, the idle became high. Normal hot idle was about 900 rpm, now it is 1100-1200 rpm, and after driving at freeway speeds (70-80 mph) it runs around 1800 rpm when I pull off the road.

I suspect this is a vacuum leak. I pulled the hose off the warmup air valve and plugged the hose and the valve. No change. How and where can I check for vacuum leaks?

The airbox has a popoff valve, but it doesn't seem to seal very well. It has been on there for years, and this problem is new.

I have had a few backfires over the years.

 

don't over react .... when I have been doing some long distsnce high way driving it occasionally does that in hot weather . Within a few lights or even the next day it is fine . If you start your car the next day and everything is back to normal I wouldn't worry about it .

 

Inspect throttle linkages. Make sure the throttle is being allowed to close completely. Got cruise control? Check cable, and again make sure it is allowing the throttle to close completely. I chased a high idle problem for several months only to find that after reassembling things after some work on the engine, that the cruise control cable was too tight and not allowing the throttle to close. Fixed in 2 minutes after trying to figure it out for months.

Brett

 

I agree, check for tension on the cruise cable. Bob b

 

I have owned and driven the car for about 12 years. This high idle is new.

I did check the cruise-control cable. It's not the cause.

 

But did you check the mechanics of your pedal, throttle cable and linkage to make sure there is no mechanical issue?

Did you install any Toyota parts recently?

 

My car was high idling because of the decelleration valve. When the car is fully warmed up and then driven for a while, it will idle from 1,200 - 2,500 rpm for a few minutes till it cools and then go back down. I disconnected the vacuum hose from the decelleration valve and it eliminated the symptoms. The next step is to see what I can do to repair the decelleration valve.

 

Check the bell crank under the accelerator pedal. If it becomes bent to the right, it will cause the accelerator cable to bind with the clutch cable and may get caught there, a la Toyota. Even if that's not the cause of your idle problem, it's a thing worth checking.