So, I have a 2001 2D Blazer with a 4.3L that sometimes revs WAY up (over 3G's) when I push in the clutch. It doesn't alway do it, just sometimes. There really isn't a pattern to it either. Sometimes it does it after I've driven it for awhile, and sometimes it does it right after I start it off and take off somewhere. There are other times where I'll drive all over town and it won't don't it at all. The throttle positions sensor was replaced maybe 3 months ago, but it had been doing the same thing off and on before that anyway. Usually the only way i can get it to idle back down is to leave it in gear and almost stall it out when I am coming to a stop. It won't rev up if I do that. Any help would be GREATLY appreciated! Thanks

 

I'm having almost the same exact problem. 02 4.3 vortec ... it revs up when I shift. Only between 2 and 3k rpm say I shift at 2k it will rev up to 2400k and back down. No check engine light.. I've replace iac, tps cleaned egr. No obvious vacuum leaks. Cleaned throttle body. It runs good just annoying. No misses no knocks. Not to sure what else to do. Any help or opinions? The check engine light goes off an on , saying engine not reaching proper temp. I replaced the t stat and ect. Runs at right temp now. Is it possible engine is stil in high idle or something crazy . Trying to get the temp up.?

 

Sticky IAC, dirty EGR valve, crack in vacuum T or hose or bad brake booster.
The big ? How's the idle on cold start? Mine never goes over 1000 and settles in a few secodns to 750 then 650-700 warm.

Read all the codes out and post them.. INCLUDING pending codes...dont interpret them. If you were good at it, you'd both probably have the problem fixed by now.

BTW.. welcome to the Forum! Like I say to all newbies.. Which I was just last year.. This aint facebook.

 

P0128 is the code. Coolant not to temp.... .I cleaned the egr. It moves smoothly. Iac is new no change . When I start it it cranks fine to about 1100 then back down to 750 ish. The only thing I can think of is a small vac leak somewhere. I pluged brake booster no change.

 

Any solution? I have a silverado with a 4.3 that's doing the same.

 

glitch - your problem sounds like a sticky EGR. I had a '94 with that very same problem. had it back to normal with a can of B-12, some pipe cleaners, and a spline drive screwdriver.

marty - can't help ya man. you've already hit everything I woulda thought to do. best I can tell you is when the engine is cold and not racing, use a can of carb cleaner with a spray tube and start shooting around vac lines. the engine will rev and come back down when it sucks it in. at least give you an idea where to look.

 

Turns out mine was the clutch switch/sensor mounted up high on the clutch pedal. I thought it was just for cruise control and to prevent starting the engine with the clutch engaged. Apparently it controls engine revs also when you disengage the clutch to shift.

 

I know this thread is old but has anyone found a solution. Already cleaned egr valve, pcv valve, maf, and no apparent vacuum leaks.