my rpm fluctuates during idle (especially when engine not warmed up yet)

[dna]

In the last few months, I have noticed that my engine fluctuates, on occasion, during idle. If it does happen, I find it normally happens within the first 15 minutes of being started. My normal idle rpm is 600. When I get this fluctuate, the rpm fluctuates from 600rpm to 400rpm, then back to 600rpm and back to 400, etc, etc, etc. Once I drive off, everything is fine until the next red light. Then I may or may not get this. In a very few rare cases, the engine has stalled too due to the low 400 rpm.

Other than that, engine is strong and no other signs of problems.

Can someone give me some suggestions to what the problem may be? Could my plugs need replacement? Could it be the plug wires?

Thanks

[Planohummer]

H1/2/3?
what year?

[Pure_Justice]

Hey DNA,

Had a similiar problem with my old vehicle. Without knowing what maintence has been performed on your vehicle and state of your vehicle, I can only speculate as to what is wrong, but here is what I did.

1) Up my octane from 87 to 89 with a octane booster, then next will with a fuel injector cleaner. Cheap gas from the wrong gas station has a way of ruining your engine sometimes, especially when they don't always give you 87 octane gas.

2) Changed out spark plug with platinum single elements. Whatever you do, DO NOT use platinum 4's. The resistences on the elements are not made for most trucks.

3) Change out air filter

4) Check all vacuum lines and tighten if needed.

I usually like to take the cheap approaches first, then when that doesn't work, I hit the manuals. Then if that doesn't work, the mechanic.

Good luck, hope I was of some help.

[HummerHippy]

I have had a similar issue, that is intermittant so it's impossib;e to show the dealer...
Can be warm or cold engine, first noticed, while driving down highway, doing 65, RPMs at 2K or so. As I get off onto an offramp, push in clutch, take it out of gear, and RPMs stay at 2K. They dont come down until the truck comes to a stop. Which means engine revs for 5-10 seconds.

[HummerMann]

I had the same problem with my '04 after it got about 30,000 miles on it. It was a rough surging idle when cold, that got better but was still rough warm. The dealer suggested a can of injector cleaner and switching to premium gas. It worked and saved me from one of those expensive injector cleanings.
I was so thankful for the honesty of the service department that they got my business when I bought my '06 H2. Give it 300 miles and use a can of the injector cleaner on consecutive fill ups.

[dna]

Thanks for the aguys. I will try the iunjector cleaner, and then the new plugs if still needed.

BTW, it is a 2003 H2 with about 60000 miles. Has been very good to me over the last 4 years. Other than very frequent oil changes and cleaning the K&N filter annually, I have done no other service.

Thanks

[Planohummer]

clean throttle body/plate and MAF, should take care of you. There's a PCM reflash from GM for that condition but it only applies to when you put it in park.

[CBR_Raven]

Originally Posted by dna

In the last few months, I have noticed that my engine fluctuates, on occasion, during idle. If it does happen, I find it normally happens within the first 15 minutes of being started. My normal idle rpm is 600. When I get this fluctuate, the rpm fluctuates from 600rpm to 400rpm, then back to 600rpm and back to 400, etc, etc, etc. Once I drive off, everything is fine until the next red light. Then I may or may not get this. In a very few rare cases, the engine has stalled too due to the low 400 rpm.

Other than that, engine is strong and no other signs of problems.

Can someone give me some suggestions to what the problem may be? Could my plugs need replacement? Could it be the plug wires?

Thanks

did you ever figure out what the problem was...my H2 just started doing the same thing a few days ago.

[splne1]

Clean the MAF and change the plugs maybe even change the O2 sensor for good measure.

[CBR_Raven]

i've already cleaned the MAF sensor...is there any way to diagnose the problem and find out exactly whats going wrong without taking it in to the dealer