the i5,3.7 eng has 5 cylinders and 5 plugs, and 5 coils,one on top of each plug,buried under the air baffle on top of the head. u cant see them.
u mite want to spend some time reading whats already been posted a hundred times. have at it!

 

Update:

Actually did stall out today after fluctuating RPM. Turned right back on immediately but still dipping up and down on the RPM. Time to take it in...needs an oil change anyway...throttle body sounds like it could be the issue.

 

Isnt this the same header / valve issue as all of these posts? https://www.hummerforums.com/forum/f...splay.php?f=34

 

i had an 07,from 37000 to 57000 and now a 2010 with 6000. they idle smooth at 700 at startup for less than 1 minute,then drop to 600 and run smooth and steady at all temps from -10 to +95 ambient. normal is steady,its not a temp problem,fuel or air.

 

I've taken it in and its giving a "misfire" code. Dealer told me the cylinders are not getting proper air and fuel because throttle body is gummed up. Well, I had throttle body cleaned last week when I had oil changed. They are telling me I need the 3 year maintenance which will flush everything but its $1,300!!!! That seems absolutely crazy...

Don't know what to do...

 

get a 2nd opinion,sounds like they dont know either

 

Let me get this right.
You have a dealer who says a drain and fill of ALL fluids (axles, t/case, trans/engine, etc.) will cure a misfire code. Does he want to flush the electrons in the ignition system too?

Please, tell the dealer this retired GM service engineer says he is so full of **** it is probably squiriting out of their ears.

Tell, him to find a tech who can read the diagnostics in a service manual, knows how to use a tech 2, and troublehoot until the problem is fixed.

 

Bad techs at dealers can be so frustrating. I had a Jeep Commander which had problems and one dealership I took it to was soooooo bad. I don't even want to start on a rant about them b/c I'll be at it all night. I just got my H3 in Feb so I haven't had to take it in yet. Let hope the Hummer dealer here is better than that Jeep dealer.

 

That's what I was thinking. The freaking check engine light was on...that doesn't happen when fluids need to be flushed. They said the cylinders aren't firing properly because they aren't receiving the proper amount of oxygen and fuel (isn't that the definition of a misfire?) and the throttle body needs to be cleaned and the spark plugs changed to help it fire properly...Still an expensive fix and I'm not sure its really the problem...

 

Just start with one thing at a time. Change the plugs yourself, then the air filter, then clean the MAF. All easy jobs. Drive it for a day between each item. Plugs made the biggest difference.
Made huge changes in mine after I threw a code briefly.
Much better mileage now (17-19)and runs very smoothly.
Plan to do the throttle body this weekend as there's still just a little bit of a dip yet.
Do all of this before letting the Stealership look at it again.