94 Blazer will not run below 1500 rpms. Changed tps, ECU/prom, fuel relay, fuel pump, fuel pump regulator, Egr valve and soleniod , .....Thermostate sending unit, and oil sending unit... oxygen sensor.
( Full size 350 V8.) :banghead:

Check for a vacuum leak.

I have checked that already..Thanks , I can use all the advice I can get.

Is the "Service Engine Soon" light on? If so, what codes are stored?

If the engine is equipped with an IAC (Idle Air Control) valve, it's possible the valve or circuits controlling it are faulty. It may even have carbon deposits around the pintle keeping it from closing completely. As 93LT mentioned, a vacuum leak would also cause high idle speeds. Have you checked the power brake booster for vacuum leaks also? Another possibility would be the throttle plate is not closing completely. The MAF (mass air flow) sensor could cause this however, it would most likely turn on the SES light.

As Old Master mentions, if you do have an IAC and it has been unplugged, there is a good chance it needs to be reporgrammed. Only problem is I couldn't tell you if the full sized blazer has one much less can utilize the reprogramming technique that is required of the S series blazers.

Have changed (IAC), followed procedures for adjustment. Now engine will not idle if rpm drops below 1300-1500 rpm. Runs great on highway, stop and engine dies.

Is the "Service Engine Soon" light on? If so, what codes are stored? Have you tried plugging the vacuum line to the power brake booster? Is the throttle valve fully closed? Have you cleaned the MAF with brake cleaner? Make sure there are no vacuum leaks between the MAF and the throttle body.

I have checked everything you have suggested , FIxing to check the knock sensor..

The engine light does not come on.??

old master , I have cheked everything you have suggested, seems fine. GOing to check the knock sensor.???

The knock sensor has nothing to do with idle speed. It's sole function is to let the ECM know when spark knock is detected. The ECM will retard ignition timing until the knock sensor no longer detects spark knock.

The only other thing I have heard is about the ignition switch itself. ?? I am running our of ideas..

What about the "Service Engine Soon" light? If you turn the key to "RUN" without starting the engine does the light come on?

yes it does..

I over looked what you said about the "Service engine soon"

Does the "SES" light stay on after you start the engine, or does it go off?

It goes off.

There's one more thing I can think of, and that would be if the vehicle is equipped with cruise control. It's possible that the cruise actuator cable is holding the throttle open slightly. It's doesn't take much throttle opening to get 1500 RPM. If that's not it, you're going to have to probe the signal return circuits for each sensor to check voltages, especially the TPS, it should read 0 at idle.

Sounds like a vacuum leak to me. Check all vacuum lines going to and from the intake.

There will be 3-4 lines running into the plenum. Also check the connection going to the vacuum ball.