High Idle

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chevyjack

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98 4.3 5 speed. Lately usually within initial startup, but have noticed after 20 min drives as well. I will pull the truck out of gear at a light, and the rpms will rev up to about 2k for about 5-8 seconds, then fall back down to normal which is about 800. Would this be TPS, or IAC?
 

chevyjack

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The truck on the first start in the morning actually idles normally at 800 before I put it in gear. It does not start idling high until after I drive it then sit at light.
 

sewlow

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Same prob here, too. '97 4.3.
Start the truck, even when it's warm & it'll jump up to around 1500rpm then sit there. Works up to 2000rpm then back down to 1500. After a few minutes (minutes!) it'll slowly drop down to 850.
Does it while driving, too. I can take my foot off of the gas & it'll hold 1800rpm. Like having cruise control...that won't kick down! Can be a bit freaky at times.
Recent intake manifold gasket job. No vacuum leaks. Sprayed down the whole engine with different fluids. No effect.
This is killing any kinda fuel mileage.
Stuck injector? Spider gone south? IAT? TPS? Thermostat? Computer glitch?
I'd kinda like a point in the right direction before I start throwing $$$ at this thing.
 

sewlow

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Still does it, but it's occasional now. Runs right more often than not. It's been a busy last 6 months, so haven't had much time to work on my own stuff.
 

lxe4

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my 5.7 was doing this for a while. was also using lots of oil and fouling plug 4 and 6 every 500km. turned out to be the infamous intake gaskets. i thought the 4.3 was less problematic for that but im guessing it still uses the same junk style intake gasket.
 

Richard Jones

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I had a high idle problem for about a month, had to go through all the trial and error methods to find the problem, ended up being the connector on the IAC. I plugged the IAC hole and it ran fine, replaced the IAC and nothing, replaced the plus for the IAC and problem solved. You didn't mention if you had a check engine light on?
 

sewlow

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my 5.7 was doing this for a while. was also using lots of oil and fouling plug 4 and 6 every 500km. turned out to be the infamous intake gaskets. i thought the 4.3 was less problematic for that but im guessing it still uses the same junk style intake gasket.

The intake manifold gaskets have been done 2x now on my '97's 4.3.
The first time I paid someone to do it.
"Did you you use the GOOD gaskets?"
"Yea, yea."
"No. No you didn't!"

I lost the 4.3 in my '98 because of I.M.G. failure.
 

chevyjack

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I dont have a check engine light. But the other day I took the throttle body off, and cleaned the bore, and blade spotless.put it back on and it ran noticeably better. Still idles higher than normal occasionally when pulling out of gear at stop light, as opposed to most of the time before I cleaned it.
 
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