Hi I'm new to the forum so hi everybody. I have a problem with my h2 I'm getting a misfire on 4&5 cylinder only at idle. While driving there is no problem at all. I changed spark plugs ,wires, maf sensor, map sensor, injectors, intake manifold and gaskets,cleaned throttle body,cleaned k&n filter,changed fuel filter,did smoke test to check for air leaks, checked cylinder compression it was about 120 psi on all more or less, checked fuel pump. The problem never went away. Check engine light is on and the code is po 300. Drove the truck with the computer hooked up and there is no miss fire only when you stop at the light at idle. Please help, I'm running out of ideas.

 

The SEARCH box above will be your best tool: I put in P0300 and got these
It would also help with the year or engine size.

https://www.hummerforums.com/forum/h...0300-h2-28394/

https://www.hummerforums.com/forum/n...t-issue-28121/

https://www.hummerforums.com/forum/g.../fed-up-26952/

https://www.hummerforums.com/forum/h...jectors-25170/

https://www.hummerforums.com/forum/h...p-11603/page3/

https://www.hummerforums.com/forum/h...ne-light-8861/

https://www.hummerforums.com/forum/h...-misfire-3051/

 

Thnx i read all the post but it doesn't look like my problem mine happens all the time at idle cold or worm engine and its 2003 hummer h2 6.0 L with 70 000 miles

 

Did you change the injectors or just clean them? Everything that I am finding seems to be clogged injectors. But there are several other things to check too. Here's some info on the code.
Automotive Technical Service Bulletin - TSB | Engine-Codes.com

P0300 HUMMER Cylinder Misfire Detected Random Cylinders OBDII Engine Light Trouble Code | Engine-Codes.com

 

I changed them new from the gm dealer

 

OK just an update I finally found the problem it was 2 cracked spark plugs I guess I bought defective ones. Thanx for all your help

 

There could be some problem with code have you checked it properly?

 

What are you talking about angel? His whole post was about the codes and how he figured out what the problem actually was and then fixed it......READ READ READ

 

ok sorry I am reading it