'99 Silverado runs poorly when partially warmed up.

[anumber1]

My '99 Silverado (4.8l, 4x4, 180k miles) has a "flat spot" at partial throttle when partially warmed up.

 

It runs fine cold, runs fine hot. Stumbles a bit in between.

 

No CEL.

 

New plugs, wires, fuel pump, intake gasket, fuel pressure regulator, fuel filter, PCV valve, air filter and cleaned the MAF.

 

It threw a code for the intake gasket 6 months ago and I replaced it.

 

The truck has been doing this for a while. No change with the new intake gasket.

 

I bought it new and i once was a gm tech (in the late 80's). I have a helm service manual for it.

 

Currently, I am leaning towards replacing the MAF but would like to bounce it off the group before spending $100 on the MAF on a shotgun parts replacement.

 

Thanks!

[00Silverado4x4]

Before anything, I'd double check your fuel pressure to ensure it's not a fuel pump issue.

[anumber1]

Before anything, I'd double check your fuel pressure to ensure it's not a fuel pump issue.

Yes, I should have mentioned, the fuel pressure is good. 58 psi and holds.

 

I did the fuel pressure regulator, PCV valve and knock sensors when I had the manifold off just because I was there.

[rjgti]

lazy 02's maybe

[anumber1]

lazy 02's maybe

Yes. I suppose I should check them.

 

I replaced the originals a couple of years and 30k miles ago. Denso sensors.

[anumber1]

Fixed it...

 

O2 sensors checked fine. Fuel trim with my scan tool was hovering around 5%. Sensor voltage looked good with the multimeter.

 

Bought a Delphi MAF (identical to the OEM one on there) from Rock Auto, installed it - fixed. Done.

 

It.wasnt bad enough to set a code but the truck runs great now. Way more power. Smoother idle. Flat spot/hesitation gone.