I bought a 2008 Hummer H2 with 74000km on Friday and noticed the idle was a little rough and holding on 500 RPM. The seller said it needed a tune up which I did. I installed a new air filter, new NGK TR51X Iridium spark plugs, new 5w-30 synthetic oil and the engine is still idling @ 500 RPM with the same rough idle. I also cleaned the carbon off the throttle plate with Carburetor spray and a rag. I need some help with the idling issue. Any thoughts?
Thanks

 

My 08 (99,xxx) had similar sounding issue I replaced plugs and wires too. I drove about 20 miles then removed all plugs and noticed that #4 and #8 had carbon build up that all other plugs did not have. I clean the plugs. Then swap coil packs and plugs on both sides of motor (so #1 plug and coil went on #2 and #2 went to #1 and so on). I went and drove another 20 miles or so then pulled all plugs again. #4 and #8 still had build up on them. Swapping the parts around indicated that it was not coils or cracked plug. I took it to dealer they ended up replacing injectors on #4 and #8 (under warranty barely). I did tell them all the steps I did prior to my arrival. It smoothed it out but still has a distinct ideal, a little rough compared to a 5.7L or 5.3L.

That's my story and I'm sticking to it.

 

Thanks for that information. I do have the old plugs numbered to which cylinder they came from. The center of the plugs are all whitish brown and the inside of the threaded area is black. I'll try some fuel injector cleaner tomorrow and see if that helps.

 

On my 08 SUT has the same thing. It idles somewhat rougher then usual V8's I'm used to hearing.

 

Fuel injectors need cleaned/replaced. The dealer can clean them with nitrogen.

 

its a 2008 with 74k Km on it would the injectors be fowled??
the mechanic used a diagnostic computer that showed #6 cyl has a miss, he said it could be the injector, coil , plugwire, spark plug or valve.
I put #2 coil onto #6 and #6 onto #2
I have to take the h2 back to him so he could read it again. the engine for some reason runs rougher as I switched the coils.

 

The only problem I have with the dealer is if they cannot simulate the problem, they will not fix it and call you to say your truck is ready and only to find out that they could not fix anything until you show up. So f*** the dealers, they are a bunch of minimum wage retards that are told what to do. I have a list of things I need fixed and they cannot fix any of it cause they cannot Simulate the problem. If they only knew anything about simulating electrical I/O they could really do there job right.

1st issue is when having the Low Fuel indicator turn on the navigation screen it turns the radio on the middle preset station I have programmed.

2nd is the rough idle on the engine.

3rd is the completely horrible rattling from my sun roof, sounds like it is about to fall apart.

4th the glove box rattles like hell at any motion.

5th the lower plastic cover on driver side rattles like hell at any motion.

Sorry for the rant, but dealers do not know how to fix anything. My SUT is still in warranty too. I thought the dealership by me was bad, I took my SUT to 3 different dealers and they cant fix any of it.

The problem is that its called a Warranty they make money off warranty issues so why not just replace everything new and be done with it???

 

I hear you my friend. Unfortunately for me my '08 H2 is not covered under any waranty due to me buying it in another province, a 7 hour drive to get there. I too have similar problems as you.
# 2 rough idle
#3 sun roof rattle
#4 rattle from speaker above glove box
#5 drivers door post pastic cover rattles in my ear.
#6 left and right side door rubber @ top to chanel water has separated from body of H2 and water leaks in when door is opened.
Thats my list of things to fix.
Steve

 

I never buy high octane gas any more because the gas sits in the tank too long before anyone buys it. The 87 gas is cheapest and gets turned over often so it seems better. I also never get gas when a tanker is filling up the station. When the tanker is filling it stirs up the crap in the holding tanks and clogs the gas station filters and your tank. Then the ethanol they put in attracts moisture and that makes your engine run bad too. Injectors are not that hard to clog if you have bad gas.

 

The only time I fun 93 octane is when I take long trips upnorth. I always run 87 when city driving.