BigSxxy

I have a 4.9L straight six. I don't know the history of this truck but it sat for about 4 years and I am attempting to bring it back to life...

I have a high idle issue. Just replaced the smog pump, alternator, battery, radiator, thermostat, clutch and ALL the fluids. This has been a hell of a project.

My idle stays high even after the engine has reached temp. I was hoping a drive down the freeway would help calibrate the Computer, but no such luck.

I know I can spend a load of time and money on these sensors and emissions stuff. I'm just wondering what area to start in and maybe hear if this is common or not. I am new to this forum and it appears to have a lot of information on it.

Thank you for any input!!!

letsroll13

Yes I am having the same problem now. Mine was kicking and want to die when I pushed the clutch in, so I replaced the IAC and the PVC and grommet and know when I first start the truck in idle up then down but as I drive it starts idling high cant figure it out I tried chasing the pvc hose but can't figure out were it ends and I didn't find any leaks around pvc or iac.
I hope someone will have an idea to start out now

aandrews109

I had a 1990 150 4x4 with a 4.9 and it did the same sort of thing while under warranty. Ford said it was a MAP Sensor issue. According to the dealer, that is what they replaced to solve the problem. The other symptom it had was a surging idle and almost stalling if you were easing along and pushed in the clutch. Hope this helps.

Also check the vacuum line to the MAP Sensor. It may be a hard line and could have a crack in it that you can't see. My '93 Lightning's hard vacuum hose cracked and I had some weird idle issues particularly when the engine was cold and until it warmed up.

helluvaking

I was given a 1991 Ford F150 4.9L Inline Six in the spring of 2011...Yeah! I love Ford vehicles. I think they are as American as apple pie. Well this fall of 2013, today as matter of FAQ, I think I got it. Remanufactured Cylinder Head, Gaskets of choice, Plugs, Wires, new vacuum lines of choice; all in all from the MAP to the O2, Replaced cracked lower intake manifold, Replaced all sensors, New flywheel, clutch, slave cylinder, clutch hydraulic line, clutch pedal pivot/fulcrum point, Remanufacture fuel injectors, Exhaust manifolds, Exhaust system(including catalytic converter, tail pipe, etc...),A>I>R> Tube into head with furell nuts, Check valve, Alternator, Water pump and fan clutch, Belts and hoses, Throttle cable, Thermactor System actuators/solenoids mounted on valve cover, and checked the ECU board(no burnt smell or discoloring. She purred like a kitten in love for the first time. The one day at the light a high idle for no reason. Pulled intake pipe from air filter and throttle body and heard a loud sucking noise. IAC open, but for no reason. The engine is warm. Okay what else to do? Checked for vacuum at the Thermactor solenoids. No Vacuum. Vacuum of the upper intake tree to wheel well canister. No vacuum from canister to solenoids. Bypassed the can. Check Engine light went out. Going for a spin. Will check back later. I'll need to adjust my timing. Timing lights are great, but I'll have it set by a trained and certified mechanic. My Distributor has an ICM mounted on it's side, and I want it replaced. Chow!