i have posted this issue before, but id like to go back to square one. in the morning my truck idles at around 3500 rpm. sometimes it will do it for about 10 minutes, sometimes it wont stop at all. i feel like the truck is going to blow up at red lights. its almost dangerous to drive since the truck fights the brakes. heres whats new:

-cap, rotor, wires, plugs
-tps
-iac
-egr sensor
-coil
-pcv valve
-intake gasket
-pretty much every vacuum line.
-all the grounds have been tested and contacts cleaned

i have never replaced the map sensor, coolant temp sensor, the egr valve itself, or the egr valve solenoid. the only codes i get are some egr codes here and there, but i dont think anything egr related could cause my problem, however the truck does buck violently at low rpms sometimes, so i think i should replace the valve anyway. sorry for the long post. all help is appreciated.

 

When its idle is high, what happens if you unplug the IAC?

 

hmm, ill try that tomorow. its such an erratic problem so its hard to test things when it does it.

 

Again, check the Vacuum Resivoir. They are Notorious for corroding, causing a massive vacuum leak.

 

Yea I agree problem with that, though it'd idle high all the time if it had a vac leak one such as that. Wouldn't be intermittent, it'd be sucking air all the time there. That and "92" model year, start of the plastic type vac reservoirs? Don't suffer the rust issue known in the metal cans?

EVR vents vacuum from atmosphere when not directed to EGR controling it, might be broke/wide open at times and then to add to the problem when its not supposed to be.
Have EGR issues might want look into that, EGR issue might all stem from be to low engine vac left over due to leak/s pull it open?

Unplugging IAC would show if it has any control over/effect of engine speed or not and or if its part of or all the problem. "New" unfortunately doesn't always mean "good" either, a problem in of itself!

 

My 93 (built 11/92) has a Tomato Can.

I just replaced it again. Second time in 250K miles

 

Good to know, had to be 94 model when they went to plastic for em.