High idle in park & neutral 95 Chevy Blazer LT/S10 4.3 vtec.
Any ideas as to what may cause this. Maybe the Throttle Positioning Switch or can it be the plenum gasket is no good ??? Please advise

 

Could be a number of things.

What testing have you done?

Have you traced the vacuum lines and/or intake gasket interfaces with an unlit propane torch while the engine was running to try and find any vacuum leaks?

Cleaned the IAC valve?

 

I had this problem a few years back, it turned out to be the TPS, but that being said, DO clean your IAC. It will make a difference. But my money's on the TPS.

 

Tests I've done.....a friend took a hose away from the top engine cover, and he sprayed combustable fluid into it and the engine idle dropped. He said it could be that the plenum gasket is shot. Also, someone else suggested to clean the EGR sensor or try replacing the TPS (Throttle Positioning Switch). So, should I try cleaning the EGR sensor 1st.....then try replacing the TPS 2nd....finally, have the plenum gasket replaced.

Also, after about 5 mins. the temp rises too!! about 220 degrees or higher. The thermostat does open up and it goes down again, but then it keeps cycling like that over and over again.

The engine is new, and all parts to it too!!!.....about 3500 miles put on, so I'm hoping it's just either the EGR or TPS.

You mentioned cleaning the IAC....where is it located and how do I do it?

Thanks for your reply.....I put a little over $4500 and would like to keep the fix cost down now as much as I can.

Thanks,
Don

 

When we unplugged the TPS....nothing seemed to happen!! Should'nt it have lowered the idle, if the TPS was no good??? Also, where is the IAC located and how do I clean it?

 

Spray some carb cleaner around the radius of the plenum gasket-as your buddy said. If the idle drops then...whola..Jp

 

The IAC is located on the throttle body, left side top, as you are facing the engine. Two torx bolts hold it on. TPS is on the right side of the throttle body.
I use electrical cleaner, spray the pintle (sorta looks like a bullet slug) and everwhere there is carbon buildup on it. You could use Throttle body cleaner on it as well. Also clean out the area where the pintle goes into the throttle body.

 

marcspector,
Ok, will try this.....keep you informed afterwards.....thanks for your help, deeply appreciated.

 

Peru Motors,
Ok, will do.....thanks for the info....!!!

 

Has anyone ever gotten bad gas that spiked your rpms? I put 51L (50$) in my 2001 jimmy yesterday, went thru almost all of it like 200km, and after about I dunno half the fuel, my idle spiked to 900 rpm in park, today I called a friends shop and he said to try a fuel system anti-freeze, and get gas from a different place, my idle dropped *** soon as I re-fueled and ran thru all the **** gas, just wondering has that ever happened to some before?

I also checked all my vacuum lines and cleaned all my throttle connections/plugs, as well as took her for an Italian Tune-up,

thanks in advance,