I have a 1989 F150 w/ 5.0L. The idle sounds like it's at 1500 rpm and doesn't drop down when the engine warms. I think I have a vaccuum leak, and I think I can hear a hiss, but the engine is running so fast it's hard to tell. The brake pedal seems to go down farther than usual also, even though it stops ok. If I do the carb cleaner spray, will it increase the rpms if the leak is in the brake booster line/hose? I did remove and clean the IAC because I thought that might be the problem with the engine dying when you come to a stop with AC on. I cleaned the IAC with carb cleaner. I don't think so, but could I have done something that would cause the problem. It didn't have high idle before I did the work, but I was careful. The only codes are KOER 12 (cant control rpm during self check or problem with idle speed control) and Memory code 54, which is (air charge temp or vane air temp sensor voltage is too high). Would the ACT causee the high idle? Thanks for any help.

 

What work did you do? Check over your work and look for cracks in grommits and hoses, fittings etc. Plug the brake booster line at the engine. If the idle goes back down the brake booster, hoses and fittings are the problem area.
Reconnect the brake booster vacuum line and disconnect it at the brake booster vacuum check valve. Plug that end and if the idle goes down it is not the hose.
Plug it back in and unplug the check valve at the booster and try again. If the idle stays high it is the check valve. Look closely at the rubber grommit on the booster that the vavle fits into. Is it cracked or otherwise damaged?

JMC

 

I am original owner and I'm fixing it up for my son to drive(I have an 04 Screw). Anyway, I only changed a water pump gasket and then removed and cleaned the IAC to see if it would stop dying w/ AC. I will try your suggestions on brake hose. Thanks.

 

As suggested by JMC,(thank you) I checked the brake vaccuum hose..no change. I checked other lines also..no change in high idle. Rechecked the IAC and found a piece of what looks like charred rubber, can't really tell. It was about 3/4 in. long x 1/8 wide. Removed it and reinstalled IAC. Idle back to normal and passed KOEO and KOER tests. Took it for test drive and could barely keep it running. Still had the Memory Code 54 for ACT. Could that be a problem or do I just need to get EEC back to normal? Am I supposed to disconnect battery for awhile? Thanks