My '98 Suburban has a rough idle when it's cold, but only for maybe 20-30 seconds and then it goes away. Any ideas?

stuck fuel injector,it's fairly common.Run some fuel injector cleaner in the tank (every 1500 miles) and change the fuel filter every 15,000 miles.GM won't do anything about it till 1 is inop then they will upgrade to newer version.You should of gotten notice from GM ststing the extended warranty coverage for the injectors,I believe it is 10 years or 200,000 miles.

Quoted: stuck fuel injector,it's fairly common.Run some fuel injector cleaner in the tank (every 1500 miles) and change the fuel filter every 15,000 miles.GM won't do anything about it till 1 is inop then they will upgrade to newer version.You should of gotten notice from GM ststing the extended warranty coverage for the injectors,I believe it is 10 years or 200,000 miles.

any info on this?...I've got a 98 with well under 200k.....same deal...rough idle, and I do change out the fuel filter yearly, and run cleaners through it on a regular basis.

Fuck I've got 265k miles on mine. Fuckin figures!!!! I'll change the fuel filter tomorrow. Any idea on how to find out which injector it is or do I have to change all them bad boys out?

Quoted: Fuck I've got 265k miles on mine. Fuckin figures!!!! I'll change the fuel filter tomorrow. Any idea on how to find out which injector it is or do I have to change all them bad boys out?

well.....if it is a Vortec engine....you have one injector with 8 nozzels..looks like an 8 leged spider. inside the intake manifold.

lol you

Quoted: Quoted: Fuck I've got 265k miles on mine. Fuckin figures!!!! I'll change the fuel filter tomorrow. Any idea on how to find out which injector it is or do I have to change all them bad boys out? well.....if it is a Vortec engine....you have one injector with 8 nozzels..looks like an 8 leged spider. inside the intake manifold.

really i thought all 8 of those were injectors...so is it a nozzle that's plugged or just the main injector?

The main injector is in the center.....look on the drivers side of your intake to the rear of the throttle body...you'll see two stainless lines going into the upper intake, with a large electrical plug next to it.

The injector has 8 plastic lines  coming out of it and running to it repective cylinder intake port.
Apparently the nozzles get clogged.

GEN 3 Vortecs V6,V8 in 95-98 C,K,L,M.Gvan and 96-99 and some 00's have 2 different injector systems.The original system is a fuel meter assembly with 8 individual injector assemblies(solenoid/line/nozzle) that can be replaced individually,the solenoids fail.nozzles get plugged and the lines plug up and cause problems when you remove fuel meter assembly to replace injector/s
after replacement,more injectors take a dump requiring teardown again.GM disc using nitrogen to blast them open.Now the fix is to replace with an updated fuel meter/injector assembly(spyder)
just like the older Vortec V6.The assembly is located  under the upper intake plenum
(black plastic intake)and above lower intake manifold.Tis is best left to somebody who knows these engines.I have replaced a few engines from people not knowing to be careful not to drop the fuel delivery line locknuts down inside.The only way to pickup which inj is misfiring is with scanner or tech2 and watch misfire graphic,do not confuse cold misfire/rough idle with misfire under load usually noticed on uphill grades-totally different problem.Also these engines have a tendency to develop a constant real rough idle/possible no start,yet another Gm trait.

I had a similair problem with my 97 Dodge.  It turned out to be the IAC, idle air sensor.  I pulled mine, freed it up and cleaned it, and my truck runs fine now.  I still bought one for when the original unit fails.  

good point CSM......I had planned on pulling my throttle body to perform a airflapectomy*  [modification] and cleaning it out would probably be done as well.


* don't try this at home.....I'm an ASE tech...and I can really screw things up.

If it's misfiring at idle on up, it's usually the injectors, check with your dealer on special policy on the injectors in your state, they can be cleand with nitrogen and them a cleaning solution. If your engine misfires under load, it's the valves, sticking in the valve guides, you'll need to pull the heads and you'll find the valve guides are machined too tight.

Check these after checking the basics, like tune up, compression check etc, the sticking guides can be found with a vacuum gauge, to i.d. which cylinders you'll need a Tech 2 the factory GM scanner.

Sorry to tell you the valve guide issue is not a special policy, one fix another guy at a GM dealer told me to try if you don't want to pull the heads is run synthic oil changing it every 1K miles, I've never tried this and have no idea if it works.

Last point, if you put aftermarket tuneup junk in your engine, that can cause misfires too, only used A C Delco parts on tune ups.

Quoted: If it's misfiring at idle on up, it's usually the injectors, check with your dealer on special policy on the injectors in your state, they can be cleand with nitrogen and them a cleaning solution. If your engine misfires under load, it's the valves, sticking in the valve guides, you'll need to pull the heads and you'll find the valve guides are machined too tight. Check these after checking the basics, like tune up, compression check etc, the sticking guides can be found with a vacuum gauge, to i.d. which cylinders you'll need a Tech 2 the factory GM scanner. Sorry to tell you the valve guide issue is not a special policy, one fix another guy at a GM dealer told me to try if you don't want to pull the heads is run synthic oil changing it every 1K miles, I've never tried this and have no idea if it works. Last point, if you put aftermarket tuneup junk in your engine, that can cause misfires too, only used A C Delco parts on tune ups.

It's only when the car is first started, and doesn't last very long. I'll figure it out once I get some freakin time off work