Well I have spent some time going over many threads on this site and it is very informing but I have yet to find the answer.
As it seems to be a problem many are having I feel mine is a little different.
Just picked up this truck and it's in great shape, even the motor is new since PO changed it out with a crate motor which now has 5000 miles on it.
Now my problem is the truck runs like a champ once warm but will not idle on it's own when cold.
I removed the IAC and verified it's movement. The solenoid will not move full stroke even when I jumper it directly to the battery. Removing the connector during hot idle does not change RPM as mentioned in other threads.
Pulled the codes and only got 552 KOEO and 412 KOER. Looked around for vacuum hose problems and none found.
I tried a new IAC and the engine revs high maybe even very high and never settles down even once the engine is at temp. I have no Tach so I can't say what RPM.
Re-installed the old IAC and everything runs normal except for no cold idle condition.
Now my question, since I found nowhere a mention that I should reset the EEC after replacing the IAC I was wondering if that would have been the missing step in this procedure.
Every little bit of anti-pollution and canisters all check out since they were either replaced or reconditioned during the engine change.
TPS sensor ohms out within spec stated on Ford Fuel Injection.
I have not verified ACT or ECT as of yet. I think the ECT sensor is in front mounted on or near the thermostat but have yet to find the ACT anywhere.
I do not suspect those parts for the time being due to the fact that fast idle occurs upon changing the IAC though fast idle conditions don't go away and with the old one it runs great.
The plastic vacuum lines are well known to be brittle and leak. In most cases a vacuum gauge alone will not show the true story. I used a hand held vacuum pump/gauge to test each vacuum circuit independently on my '92 F350. Most of the plastic lines we toast. I replaced each of them as well as all the rubber lines. My "coffee can" reservoir behind the driver's side headlight was rusted through. I also found the PO had attempted to repair the vacuum reservoir on the blow motor/evaporator case, but failed miserably. Once I fixed all those leaks my truck idled much better, but still a little on the high side. I ended up also replacing the gasket between the upper and lower intake manifold. Now all is good. I did test my idle vacuum before and after replacing all these pieces. With all the leaks it was ~15" warm, after all the leaks repaired ~16.5". Both are in range, but now the idle RPM is correct.
You stated your TPS measured the correct ohms, but did you measure the voltage at idle? I always remove the power to the EEC after changing any sensor. That will erase any long-term fuel trim adjustments the PCM may have stored.
I'll triple check the vacuum lines, as for the gasket I mentioned in my previous post that this is a new crate motor that was installed just 5000 miles ago and all the gaskets are new including new exhaust manifolds.
The PO used the original intake and such since he striped the old block to install the new one.
You mentioned to reset the ECC when a sensor was changed, is it the same for actuators?
Remember the motor runs great with the old IAC except for no fast idle on cold mornings and with a new IAC it runs fast and never comes down to a regular idle.
I will look at the voltages from the TPS sensor as soon as possible, I need to finish overhauling the cab for my payloader before our 1st snowfall which should be coming soon.
I just have a hard time believing the TPS could be out of whack when it idles perfect once warm and pulls great even under heavy load.
I don't know much of these 1st generation FI systems since the Jeep is carbed and for the Subaru I have a ECUTEK programmer which gives me the problem and solution.
Thanks for your feedback.
Sorry about the repost.
As for the coffee can behind the drivers headlight, I do not have one, I do though have a plastic one like a coffee can (passenger side) and an other one right next to it which has the red and white hoses going to it.