99 454 rough idle
 

My 1999 454 suburban idles poorly, it nearly dies sometimes but recovers.
It runs great at startup, cold, but after about 30 minutes, idles rough.
It has 175,000 miles on it,1000 miles on intake gasket job, hoped that would the fix rough idle. New fuel filter didn't help. I think it may need injector replacement or maybe a knock sensor. No I haven't pulled a code yet...

Re: 99 454 rough idle
 

IS the check engine lamp on? That would be the first step.

Could be an IAC problem. It could be sticking or gummed up. How did the throttle body look? All gummed up with crud?

The biggest problem with the injectors on these is they leak after the truck is shut off. Usually it will be hard to start and have a pretty decent misfire until all the excess fuel is burnt off. The FPR leaks too.

Both of my vortec 454s idle fairly low, about 425 at normal operating temp, but its nice and smooth.

Re: 99 454 rough idle
 

no check engine light, throttle body was cleaned out well during intake gasket rebuild. Mine idles warm about 5-600, but seems to "stumble" and nearly dies, like an old Quadrajet with a bad filter. Fuel filter is new.

If injectors leak overnight and it runs well cold..hmm. It almost feels like a fuel PSI issue at warm idle.

Re: 99 454 rough idle
 

Sounds like you need to test the fuel pressure as well. Need to test with key on engine off and key on engine running, the latter preferably with it hot to duplicate your poor idle condition.

Also, I see this thread and your tensioner thread are in the wrong areas of the forum. The more correct area is the one prior to this one. Your '99 Suburban is still the GMT-400 platform which technically ran to 2002, the years are really general guidelines. I always suggest that people post within their bodystyle of vehicle.