OK, I just bought a 95 Blazer knowing it has this issue. It was a great deal and I know the family that sold it well enough to know that they wouldn't screw me over on the deal.

The truck has about 260,000 miles on it with the 4.3. The high idle issue comes and goes but is worse when it's cooler outside (55 and below it seems). The engine cranks over easy and then revs up to 1500 rpms and stays there. When you put it into drive from there it lurches so you have to be hard on the brakes. (not good on the u-joints, which have been replaced recently) After you drive about 15-20 miles or so the problem usually goes away.
The previous owner tried almost every fix that I have found and nothing has solved the issue yet. He has done the following all within the last 20,000 miles...
-Installed a re-manufactured computer...which solved the problem for about a month
-replaced the cap and rotor
-spark plugs and wires
-replaced all the gaskets around the manifold and such
-cleaned the IAC valve
-replaced throttle position sensor and wiring harness
-new injectors
-cleaned EGR and added screen

What else is there that I could possibly do? I though of replacing the temp sensor and IAC valve. While I'm doing that I'll clean the MAF sensor and throttle body. Also going to check all the vacuum lines again. Could it be an O2 sensor?

I'm just lost as to what else I could possibly do to fix this issue. If anyone has any other ideas as to what the problem could be I'd love to hear it!

Oh....and its a 4x4 with a W code Vortec motor. There is a crack in the top of the radiator that the previous owner tried to seal....didn't work so they run the coolant a lil low....could that cause the problem?

 

And before I get told to use the "search" feature, I have done so....that's where I started!

 

No one is getting grumpy at you it's just sat.
I have a 95 and every time I had a high idle problem it was a vac leak.
These guys are starting to get a little old and there are a lot of vac lines to get old.
Start at the purge valve, it's over on the right side and has a strange configuration of lines. As they run towards the front of the motor it switches to a formed plastic line. Had a heck of a time cause it was cracked were you could not get an eyeball on it.

I would start there.

 

I wasn't accusing anyone of being grumpy, its just that's always the first answer to a thread like this I see.
I'm gonna have to go vacuum leak hunting! Doesn't that sound like a wonderful way to spend labor day!?.......

 

Vac lines are fairly cheap to replace as well...right? I replaced the TBS and it hasn't idled high yet. But it was warm out so it might be the heat. Also cleaned the IAC valve. If it idles high next time I'm looking for vac leaks. What's the best way to find them?

 

When I go hunting for vacuum leaks I like to start by inspecting all the vacuum lines looking for cracks or breaks. If nothing comes up on a visual inspection I like to take the main vacuum line off the back of the manifold and put a hand vacuum pump on it and work my way down each branch line from there trying to find the leak.

 

plug all vacuum lines, only 2 ports on back of upper intake, and see if problem persists. Vacuum goes to the vent control, power brakes, 4x4, cruise (not sure about 95) and vacuum ball.

 

So the truck will run with the vacuum plugged but just those items won't work, correct?

 

I replaced the TBS and cleaned the IAC valve and the high idle has disappeared so far. However, I did unplug the battery when I did so. So it may be that the computer hasn't readjusted to it yet. But the truck has a rich smelling exhaust so there's probably a vacuum leak lurking somewhere.
I guess I still have a project for this weekend.

 

A rich-smelling exhaust could also be leaking fuel injectors. I would recommend a fuel pressure and leakdown test.

Heck, that's just a good idea for everyone to do each morning before breakfast.