Throttle Position Sensor
 

89 Blazer, 350 motor with throttle body injection. Engine idle should be around 650 rpm but is much higher. I take it the throttle position sensor monitors the idle. Is it as simple as installing a new sensor and after start up the ECM will reset the idle?

The TPS sensor has really nothing to do with idle speed. That is controlled by the IAC (idle air control) valve which is also located on the throttle body.

Have you checked for and eliminated all other potential problems? Vacuum leaks - those tbi units are known for bad base gaskets and vacuum lines definitely have a service life. Partially hung open throttle shaft/valve?

*Moving to Fullsize K5 Tech* - The 1st gen tech area is for the 1st gen s-series.

No, to be honest I haven't checked the items you mentioned, but I will now. I had done some reading on the idle air control valve. So now I have a project for the weekend. Thankyou sir

Just wanted to update this thread. I did find the base gasket to be bad and I got another one on tonite. I probably could have stopped there but went ahead and got a kit to rebuild it. I hope to finish it this weekend and I'll update this again.

I replaced the idle air control valve and found 3 vacuum lines that were rotted and replaced them. The idle has not dropped where I need it to be so I still have a problem somewhere. When I got the control valve I noticed the dimension between the housing mount and pintle was way less than the 1 and 1/8th inches called for in the manual. It may be necessary to adjust it out some for it to work properly. Any thoughts on that?

It should adjust on its own over time, but you can adjust it out to the proper initial setting and see if it controls the idle better.