kellter

I had the same problem and it was the engine coolant temperature sensor. The ECM was running the truck like it was -34C. As soon as I put a new sensor in, idle went down to about 800 rpm.

Dino92

K thanks I was leaning towards that but wasn't sure if that was an input the ECM would use to control the iac valve

Dino92

Ok here is an update, found canister leaking, I install another canister and the idle problem has got worse, I have check with ether for vaccuum leaks and cannot find any, I have install a new iac valve, throttle body gasket, cap , rotor button, plugs and wires, the only codes I have are 411, 412. Can't control low idle or high idle during test, if I unplug iac truck idles normal. The other prob I have is when truck starts up cold it misses and acts like it's going to die then idles up really really high and stays there. If I start it when warm idle just goes up really really high and stays there. Does anyone have any ideas.

mark392001

Is the new IAC a Motorcraft? Mine was sensitive and didn't like the Autozone one I bought, preferred the Motorcraft junkyard pull. Did you replace gaskets for TB and IAC?

mark392001

Also have you checked your Throttle Position Sensor? If so and if you removed did you reinstall the right way? Wiring pigtail should be facing the driver's side.

fltdriver

Should also be placed in the hole and rotated to correct position otherwise you get funky problems.

Dino92

Yes, I replaced gasket, installed tps correctly and checked the voltage at the tps, at idle I had .92 volts at wot I had 4.97 volts. The iac valve was not a motorcraft. The funny thing is that some times it idles fine usually after I erase the codes, but it doesn't take long to mess up again .

mark392001

Sounds like the ECU isn't regulating the idle. Maybe try a junkyard ECU?

mark392001

I had an issue on mine where the previous owner had placed a small rubber grommet on top of my idle set screw to artificially raise idle, once I removed that mine was perfect. If it's not something like that have you checked the idle set screw?

Dino92

Yes I have checked the idle screw, I am wondering if the map sensoe could cause this, telling the pcm the engine is under load of some kind at idle and opening the iac to compensate