really high idle

Hi to all,my 89 4.0 is having a seriously high idle,2000-2200 rpm for about 30 sec.hot or cold,sept 05 replaced all sensors and iac,just replaced iac again 2 weeks ago,no change,weird part is it sometimes behaves and will go right to 800 rpm,no vacuum leaks,no fuel leaks,concern being that freewheeling at 228000 mi on it aint gonna last much longer.Great ride,hate to lose it over idle problem.Thanks

strange, I have the same problem with my 89 right now, but I figured it would be the iac valve as when it was running good before , I forgot to hook up the iac one time and thats exactly what it did.

if I start and it goes to 2000 rpm, I shut it down and restart until it will run with a normal idle.

if you search through the forum for high idle there are plenty of opinions, I think the TPS would win from what I have read. Some say map sensor, iac valve or tps.

Also check your B+ Latch relay.

did you ever get your idle problem fixed yet, mine still does the same, at start up goes to 2000 rpm.

On my 84 when I had it, the accelerator cable had broken the plastic tab holding it on at the firewall. The cable then had sawed a groove into the firewall and started hanging up at a high idle rpm like yours. Fix was to replace cable.

Make sure your TPS is adjusted correctly. My 88 had a few funky idle problems as well as the usual shifting ones. I did all of the usual regarding the idle, cleaning TB and IAC hole, IAC seemed to work OK, check for leaks, etc. Then while dealing with the shifting, I changed the TPS. At first, the idle was insane until I re-adjusted it.

Another thing to check other then the TPS adjusted correctly but go and tighten up all of your intake/exhaust manifold bolts - in some cases that clears up the high idle.