So I just replaced the timing belt and water pump on my 89 4runner 3.0 5 spd and some funny things are happening. Now I only took it around the block but in that short time I ran into some issues. First the idle seemed very erratic. It was jumping from 1800 to 1000 and back. Once that seemed to settle down the truck began to overheat. I limped it home and now it sits in the driveway cooling off. Now while all this was going on it did run and drive just fine. It was not down on power or accelerating abnormally. I was wondering if anyone had experienced this before? I spent like 5 hours doing this job and I sure as hell dont want to take it apart agian.

 

sounds to me like you probably got an air pocket in the coolant system.

 

second the air pocket and or bad thermostat.

hows your timiming?

 

Third on the air pocket, mine did the same thing until I topped off the coolant level.

 

Would that account for the erratic idle? Maybe the water pump wasnt facing any resistance and therefore put less drag on the driveline? Any way I will post up any changes this afternoon.

 

Erratic idle could be from your temp sensor not reading right since you probalby didn't have water flowing through it. The ECU bases a lot of adjustments to fuel/timing by the temp sensor.

Let the engine warm up with the radiator top off, then add water/coolant until it tops off (you should see the water flowing thru). Cap it, add some to the overflow, and take it for a test drive...

Let us know how it goes!