My head bolts where broken below the surface maybe quarter inch. I bought a manibolt template, carbide bits and very slow 90 degree air drill. Finally got them out without touching threads or surface of head. Paid more than I wanted but still cheaper than new head or labor at shop. Plus ended up with tools for the box that I hope to never use again but have if the need should come n

 

Well got the manifold done.So took them less then 1 hour to pull it and remove 3 broken bolts. The manifold was cracked cyl 4 to 5 had big crack. They had it welded up looks good.Hopefully it lasts. I would of just bought a new one but they said not to waste extra cash.
The machined it new gaskets and new bolts.

Now to work on the other issues.

 

Ok guys so i still have a not so perfect idle.Well its fine but if i give it gas then left off the gas the rpms drop and go very low then stumbles then evens out and runs fine but i had shop hook up to computer and there was a couple codes since last time.

P0300
B3152

Also the live data shows cyc 3 missfire and when you press the gas and let go cyc 3 will give 3 or 4 missfires and cyc 2 and 5 show 1 but then dissapears and then all cyclinders show none and then after couple minutes cyc 3 will show again and after 10 minutes of running there was 16 on cyc 3 and 2 on 5.

Could this be cause by dirty throttle body?

I have changed battery terminals and enhuast manifold gasket and crack.
spark plugs were changed a couple thousand kms ago due to random missfire. Not sure what plugs were used but probably cheap standard ones.

Any ideas?
07 hummer h3 with the 3.7

 

If you haven’t removed and cleaned the throttle body I would do it. I had the same problem several years ago and doing this cleared it up. My rpms would drop below 500 and would sometimes stall when coming to a stop.

 

Ok guys so i cleaned the maf and also pulled the throttle body and gave it a good cleaning.
My crappy idle is alot better now.

Hooked up for miss fire data and now cyl 5 had 16 misses and cyl 3 only had 3 in 4 minutes of idle. None on the other cylinders this time either.
This was different from before as before cyl 3 was the one showing a bunch.

 

I had a really rough idle and misfires, ended up needing the head pulled and the valves re-machined

 

It looks like those GM throttle bodies only last around 4 years . From then on , I'm cleaning mine twice a year . Better to put a new one in there . It's the culprit in most
problems on the H3 , including bad idle , service stability , etc.....
BTW How much is a new throttle body in the States ?? It's the same one for many GM applications , Envoy , Trailblazer , etc...

 

I clean throttle body once a year and for the most part I try to burn the same brand of gas whenever possible. Are you keeping your air filter clean?

 

Yes new aftermarket filter, I run same shell fuel and here and there i will run a bottle of techron in the tank.

My stumble jumpy idle when even i would stop at a light or rev it and let off the gas is now good just the weird random live data miss fire count showing but totally switched cylinders after i cleaned the throttle body haha.

 

I'm not aware of GM throttle bodies only lasting 4 years, nor being the culprit in H3 running issues.

BTW, throughout this entire post, I don't see where the OP has changed out the COPs; am I wrong? Typically, misfires are either spark plugs or the coils.