High Rpm At Idle

[ccso503]

To start I have a stock drivetrain on a 87 K-5 Blazer, 350TBi. The promblem is a high RPM at idle. It will go anywhere from 1200 to 1500 and stay steady. I have checked and replaced vacuum lines and Throttle position sensor as well as the coolant sensor which seemed to have the most effect on it.

 

When I drop it into gear it of course drops RPM to around 500 if sitting on the brake. Is it a computer problem or possibly another vaccum line I might have over looked?

[pennzoil29]

Do a search. Top right hand corner.

[jefferias]

e.g.r valve?

[Cadha13]

If it is a auto tranny, 500 in drive is correct and any idle speed in park is irrelevant. Fuel injected vehicles have ISC as the IAC valve and for auto trannies 1000-1500 in park/neutral sounds about right. If it is a manual 600-750 is good. But just run some carb cleaner down the hole to clean any gunk that should be good to clean out the IAC passage.

[bigBP]

Hmm, maybe the Idle Air Control Valve?. I know a couple of years ago I had the same problem with a '95 4.3L TBI. Ended up having to replace both the TPS and the IAC valve. If I remember right the IAC valve is next to the TPS (passenger side of the throttle body).