Maybe it's time for a new/rebuilt throttle body.

 

it could just be the fan. in my 22re, the idle drops about 150 rpm when the fan clutch is engaged. the drop from 750 -> 600 rpm is enough to make everything vibrate like crazy. so when the engine is cold, all is well, once the engine is hot enough, the fan causes enough drag to make everything vibrate. what happens if you just let it idle for a while? in mine, after the fan has been on for a while, the engine gets cool enough to stop the fan and the idle goes back up. so see if it oscillates between high and low. if it is oscillating, then you can just open the hood and see if the oscillation is correlated with the fan.

 

Oh well, that one got wrecked anyway. All for the best I guess

 

Okey, I'll try to clean my T-body on Monday. But what about the O2 sensor??? Could it really be it??? What are the symptoms????
I don't wanna go and change everything!!!

P.S. Could the egr valve be cleaned or does it have to be replaced?

 

O2 sensors function when the engine is in closed loop mode at steady state cruise. I doubt it is the culprit in an idle related issue. Does your runner have an egr valve? Check it if it does. Go through all emissions related vacuum lines and related devices. Check for vacuum and intake system air leaks. If your engine has an idle air bypass valve then check it's function. Fuel supply/injector issues should also be considered. Check for function of all fuel injection related senders.

 

I am going to go out on a limb and say "check you cold start injector timer". It's one of those things that sneaks up on yah. Cheap fix.

Just a quick observation. A compression test isn't perfect. But, a leak down test is when making sure compression and valves are ok.

 

Thanx for your replies.
I thought that cold start injector is only for when the engine is COLD?! If it was a vacuum line, it'd rough idle ALL the time.
I DO have an egr valve. How can I check if it works??? If it's gone bad, can it be cleaned or does it have to be replaced???

 

If it is an emissions system control vacuum line it may only leak vacuum to the engine when the particular system is called up so to speak. All of those lines are not live to vacuum all of the time. All of those little valves and senders they are hooked up to control EGR etc. A vacuum system malfunction could also cause an otherwise good EGR valve to not open or close when it's supposed to. Does your engine have an idle air bypass valve? If it does and it gets sticky it could be the problem too.

 

No, the CSI will fire every time the truck starts (CSI leaking is a common problem for 2nd gens).

Yes, you do have an EGR valve.
Best way to test it is to use a hand vacuum pump and attach it to the vacuum port on it.
Then with the engine running, use the vacuum pump and see if the idle drops.
If it does, then it is working fine....if not pull and replace or clean it.

 

Thanks for your replies, guys. Can someone summarize all the possibilities that could cause this problem for me??? I'd really appericiate it, bacause I'm very comfused!

Thanks again

 

Your head gasket is getting ready to die.

 

This ones better than the explorer one...