1990 GMC Sierra 5.7 TBI no idle

[bnwbass]

Hello all,

 

I need some help diagnosing an idle problem with my 1990 5.7 engine.

The engine starts but will only run when I have my foot on the accelerator at rpms way above idle and seems to run fine at higher rpms but wont idle.

 

So far I have done/changed out the following:

 

1. new cap/rotor/plugs
2. new fuel filter and check pressure I get 11-13 psi when running
3. new rebuild kit for pressure regulator
4. new temp sensor
5. new EGR valve
6. new IAC control valve
7. new throttle position sensor
8. check injectors spray seem ok
9. checked vac lines no leaks

I get no thrown codes on the engine light

Have not changed o2 sensor

There is no change when I disconnect vac lines or the MAP sensor

I'm just about out of things to change except ECM

 

Please can some chime in here and suggest other ideas?

 

This is a 2500HD and there is one item listed in the manual for HD only called the (fuel module) I have not changed this out.

 

Thx

Bw

 

[Friz2]

Will it go(as in down the road) okay?

My 95 had the same idle characteristics that you describe, but no power to move.

 

Bad fuel pump.

[bnwbass]

I have not tried to drive I on the road because I don't think it's safe without engine control. It will move if I keep my foot in it.

I haven't changed the fuel pump because I am getting the required pressure and plus it runs at higher rpms without issues.

 

thx

bw

[REVYCHEVY55]

Check gasket under throttle body for leaks.

[bnwbass]

How do I do this?

 

Thx

bw

[REVYCHEVY55]

Spray ether or carb cleaner around bottom of throttle body. If engine revs it's sucking air. Or just replace gasket. This was the problem with my 94.

[bnwbass]

Thx

I'll do this tomorrow , is changing the gasket a big job or like a 30 min to do?