EGR/EVP are not going to cause an idle problem.

A faulty IAC will cause poor control of idle speed...

Improper TPS voltage is a likely candidate for high idle.

So far...

I've cleaned the IAC valve twice with Throttle Body cleaner, sprayed down the IAC solenoid, cleaned the EGR valve, checked voltage, impedance, and signal on both the IAC solenoid and the TPS, sprayed TB cleaner all over the engine trying to locate a hidden vacuum leak. I checked the diaphragm of the EGR valve, cleaned the Throttle Body and butterfly valves twice, changed the fuel filter. And the problem has decreased substantially, but I still have an idle problem. The idle will wander for a minute or two until it gets warmed up (which it never used to do) and it has 'sticky throttle syndrome', even though all of the linkages have been cleaned repeatedly.

The only strange thing about this problem, is that if I stop at a stop sign and clutch in, the RPMs will hang in the 1300-1500 range, but if I then slam on the gas pedal and pull my foot off quickly, the RPMs wil settle in the 800-900 range. Strange that the pedal slam works...

I believe the 2-pin computer water temp sender- not the gauge sender which has 1 screw post as an output- tells the computer to switch from high to low idle. Maybe this could be the problem?

I was under the same high idle predicament and my fix was pretty straightforward. Under the throttle body, there is a throttle stop screw. This screw is down next to where the throttle cable connects to the butterfly. Apparently, this screw was holding the butterfly open, similar to pushing the gas pedal and causing an idle in the 1500 range. While my dad was watching the tachometer, I adjusted this screw until we were in the idle range that we wanted. You may want to try this instead of tearing off pieces to clean them to no avail. It takes less time and may be a quick and easy solution.

duplicate post

I usually hear of the IAC valve failing closed and the engine won't idle and you have to keep your foot on the gas a little. Can't rule it out though. Really I don't think taking off the cable will tell you anything, if it's stuck it'll still be stuck and there won't be any difference. Dunno if "no difference" is going to tell you the IAC is bad.

I suggest two other possibilities here.
1. Coolant Temp Sensor (the one for the computer, not the one for the gauges). This tells the computer when to switch from open-loop cold engine mode to warm engine mode. If this is bad then I would expect other performance problems to occur once warm.
2. Upper-to-lower intake manifold gasket (plenum gasket) leak. This will allow air to infiltrate in there speeding it up. I had that. You can check that with an unlit propane torch. Use it to spray propane around that gasket, if it's leaking it will suck in propane and you'll hear the engine speed up even more.

There seems to be some controvery about cleaning the IAC valve. I remember reading that you should never try to clean it with carb cleaner (which is the only way to clean it!). I think I also heard pros say though that you just have to be really careful. In any case there's also an electric motor in there to fail so it may not be an issue of deposits sticking it up at all.

need some advice here plz
 

i changed valve covers to after market and new oil cap ... the old cap had a line running to carb it broke so now its closed up oil cap and just sucking in alot of air loud what can i do to fix this and keep new oil cap and valve covers?

plase help
 

hi i have 1987 f250 with 302 efi my motor surgs and then stays at hight idel when i start it its fine for awile when it worms up the prolbms start nead help please my phone number is 619 313 7564 not good on computers so plase call