This is it in a nutshell as taken from a PM between Ymeski and myself:

That's the weird thing, the "high idle" isn't constant. When I first start it cold, it will idle around 1100 then drop to 700. It will idle there until warm, once it's warmed up, it will slowly creep up to around 850-900 rpm over a few minute period. If I nail the gas or just put it in gear then back to park, still 850-900. However, if I take off and start driving, when I come to a stop, like to park the truck, it will idle at 700, let it idle for a few minutes, it will slowly creep back up to 850-900rpm. WTF!

Any ideas?

My thoughts are either ignition or super dirty engine issues. I've found about 1/8"-1/4" of carbon on the inside of the upper intake runner the other day when I removed the TB.

So, I'm down to:

Replace the distributor and TFI (I have a new distributor waiting on my uber HOT Davis Unified Ignition "Dyna Module")

And/Or

Pull the intake (at least the upper) and clean the **** out of it so it's like new again and carbon free.

IAC, EGR, etc super clean, no codes, fuel pressure within spec, including leak down test.

If you need more info, please ask!

 

Well, Ymeski and www.fordfuelinjection.com may have come up with an answer to this pesky problem:

Warm Idle
This one tends to be more about emissions. Warm idle occurs if the engine starts and ECT rises above 185�F, we come up to a stoplight, or place it back into neutral. The computers is programmed with a target RPM for idle, typically it�s around 672RPM. Typically the computer is struggling to achieve its target RPM. 255�F is the magic number to start complaining about overheating. Let�s break it down by system. Fuel is now closed loop with HEGO switching. We are now aiming for 14.7:1 A/F ratio for perfect emissions, enrichment will occur only if the ECT is above 225�F. There will be no EGR operation at these RPM�s. Timing is mildly advanced and will begin to retard after a minute. We need hot exhaust gasses to help complete combustion and converter operation. Air is pumped into the converter, but will dump to the atmosphere after several minutes to prevent overheating the converter. The Throttle Air Bypass will be controlling idle, we need a nice smooth idle. Not to high with A/T transmissions to prevent creep at stoplights. Idle will increases 100-200RPM if the ECT or ACT is over 225�F. This RPM increase will help burn the rich mixture cooling the combustion chamber. The faster RPM speeds up the accessories, specifically the water pump and fan. Belt fans will speed up, and electric fans will need more juice from the alternator.

I'll see if I can relocate the ACT to a more suitable spot and post results.

 

I think what's not mentioned is his ACT is no longer comfy inside the original stock cold air intake system. His K&N CAI Mod has it exposed to the engine compartment temps.

 

I didn't really see a problem with what you posted in the first place, and with your second post it seems like it's functioning as described. I've had a problematic idle before, but not nearly as nice as yours.

 

Agreed. While not a driveability problem, it's not a normal attribute. I would blame it on my OCD (which I think Ymeski suffers from as well ) I can't stand something not to be "right" and certainly the engine seemingly deciding to increase idle rpm at will wouldn't seem right. Plus, if anyone else is/has been experiencing the problem we may have found the reason. I'm going to replace my ACT and try relocating it below the air filter where the colder intake air is coming from and post results.

 

just remember....the ECM references the ACT for fuel mapping...changing the operating range on the ACT will alter the fuel table... mine is in the intake manifold...right next to the head

 

Temporarily reinstalling your old air intake system w/ a new ACT would end any debate. Which there is room for until then.

 

Mine was in the original air box. The K&N intake has it in the same spot except it's kinda accessible to the heat of the engine. I'm going to replace it with a new one (I ordered the last Motorcraft one in the COUNTRY! Motorcraft is no longer producing it so, it's aftermarket for everyone else, sorry) and put it just below the air filter where the colder intake air is coming in and see if that solves the creeping idle.

That ain't happin'. Debate it is! You know I like posting controversal threads...

*dream sequence begins* - Remember your knee starting to hurt just as I posted a Synthetic Vs. Dino oil for Higher mileage vehicles thread?