hunting idle

I just put my XJ back together, I replaced the water pump, exhaust manifold, and starter. I had the battery disconnected for this. I cranked it and it runs nice and smooth, no leaks water or vac. I drove it around the block and it runs fine except the idle tends to hunt around a bit, noticeable when coasting into a parking lot or stopping at a light. It seems to run steady a approx 750 RPM, but will idle down to approx 600 RPM then back up and stablize at 750. Is this the computer readjusting? If I just sit and idle it stay a rock solid 750. 1991 Auto

Thomas

Sounds like a dirty Idle air controller. It is located in the throttle body and a throttle body cleaning will solve the problem. I took mine into the dealer and along with removing the throttle body, cleaning the IAC passage and the "butteryfly". They then reinstalled it with a new gasket, then hooked up the test set to make sure everything is working well. I'd say it is the best 1.0 hour of dealer labor I ever paid.

On my 86 Mustang with the 302 V8 I had the throttle body cleaned every 30,000 miles. It is a routine mainteance thing, just not published in the owner's manual.

After reconnecting the battery, you shouldn't drive it right away. Start it up and let it idle for 5-10 minutes without any throttle. You could try disconnecting the battery again and letting it idle on its own.