Not a 3rd gen question but please help.
My 93 S10 Blazer has been revving high and idling high. It throws a code 35 which sets when the idle rpm is 50 rpm higher than normal for more than 30 seconds.

Even when driving it will basically run at 1300 rpm by itself and do 35 mph without any foot on the gas pedal.

I tried replacing the IAC valve but I get the same results.

Any other thoughts?

Bob

 

Try taking carb spray and spray around the base of the throttle body and see if that changes the idle speed. The throttle body base plate gasket maybe blown out and causing a vacuum leak witch would definitely raise your idle speed. The other idea would be a screwed up TPS that is sending the wrong voltage to the ecm i.e. .75 volts instead of .50 volts that is should be at idle. Hope this helps!

 

Thanks for the suggestion. I should tell you that is the 4.3 liter Center Port Injected V-6. The throttle body sits out front just like on a L98.

Also I am doubting a vacuum leak because the idle will come down to around 750 rpm in drive (its a digital dash so I can't be exactly sure) but yet it still sets a code 35.

The strangest part is that it will cruise along at 35 mph without my foot on the gas. Almost like the throttle is open when it should be closed.

Bob

 

maybe a throttle cable issue.... just a thought

 

That changes things seeing that this is the 4.3 W and not the Z engine. I have seen where the upper plenum gasket has blown out. Any whistling or any other noises underhood? Did this suddenly start doing this?

 

Is it at least four wheel drive. If not, why are you owning a vehicle like that?

That's only a step above a *****.

Just teasing.

 

Yes, its a 4 wheel drive. And yes it is technically my wives vehicle.
It works much better in the snow than the IROC too.

Bob

 

My Z28 does great it the snow. According to the speedo I'm doin' zero to 60 in like 2 seconds!!

 

What is the idle vacuum reading? (I'm thinking leak.)

And for diagnosis, forget about the digital dash. Use a handheld tach, voltmeter, etc.

 

Turned out to be the upper plenum gasket causing a vacuum leak. Way to go gearhead!

Bob

 

Glad you got it fixed! Those vacuum leaks can be sneaky sometimes! Just out of curiousity was there a chunk of gasket missing?