blb

My '94 22RE starts right up, idles fine until right after the thermostat opens up, then the idles surges up and down. (I understand it is the computer that tries to bring the idle down}. After it is fully warmed up, the surging goes away and it will idle fine as long as it stays hot. The temperature gage reads normally. So far, I have replaced the radiator cap, replaced the thermostat, lowered the idle speed to 700RPM, checked all vacuum lines, and elevated the front of the truck while it was running to try to get any trapped air out of the cooling system. It still does the same thing. The surging idle only occurs right after the thermostat opens up and it stops surging after it is fully warmed up. What am I missing? Any ideas to get rid of this problem will be greatly appreciated.

kyle_22r

the thermostat opening has nothing to do with the idle. it sounds like your TPS might be out of whack.

Joyota

I think Kyle is right on. Check your TPS (Throttle Position Sensor). Go here and find out how.

blb

Ok, thanks for the replies. I checked the TPS and all of the resistance values were within the range specified in the service manual and on 4 crawlers instructions. Any other ideas?

Joyota

I'm tapped for ideas, but did you ever get this taken care of? I'm curious as to what you found.

blb

It was a bad head gasket letting combustion gasses into the cooling system. When an air pocket would pass the coolant temp sensor, the idle would rise until the computer would cut off the fuel until it came back down, causing the surging. This seemed to happen mainly during warm-up at first, but as the problem got worse, it would happen after warm-up also. This vehicle only has 134,000 miles and was meticulously maintained from day one, with a coolant change done every other year. Why are these 22RE's so prone to head gasket failure? I see many others on this board that have had head gasket and timing chain failures on 22RE's. I've had 4.0L Jeeps for years with as many as 275,000 miles and never had headgasket or timing chain failures. Maybe Toyota should use cast iron heads like Jeep does instead of cheaping out and using aluminum. This will be my last Toyota. I do appreciate the help I received from the others here and just wanted to end with a "Thank You".