Hey all, I seem to have an engine surge that is about 250 rpms.
I am not sure if it happens at idle when I am stopped or in park.
But I can see it on my tach and feel it when I drive. It doesn't happen all the time, and sometimes it happens at different points on my tach... Today it was when cruising at 1000rpms. Give it a little gas and it surges or jumps back and forth, that just a little bit off the gas (barely anything) and it stops surging.

Any ideas?

 

I would start by cleaning the throttle body, and adding some Chevron Techron in the gas tank.

 

My '04 has been doing this since buying it in June of last year. I was told on a different forum that it's a torque converter issue with the units Hummer/GM chose for the truck. Mine is really bad around 40-45 mph, in-town driving at about 1500-1600 rpm. I do feel it at other rpm/speeds but not nearly as much. Once above 1700 rpm it goes away.

Our '08 may or may not be doing it; driving in town the other day I thought I could feel it surging ever-so slightly, but couldn't detect it on the tacho.

'04 has 151k, '08 121k.

 

I was getting a vibration when tach hits 40mph like clockwork. If I press on gas and go thru 40mph quickly I didn't feel it. I had to replace my rear main seal (my friend did it for me), I had him change the torq converter also to solve this issue too. First time I drove it afterwards I did not feel it but days later it came back so I don't think its the torq converter since mine is new. I have no idea what it is. Ive been experiencing this since 50k miles and now I have 86k. Its an 2005 H2. My 08 does not do it.

 

I had seen somewhere that it could be a trans issue, but I would think that if it was a trans issue it would be a continuous thing... Not something that happens randomly at certain points in the rev range. I have changed the fluid... Haven't done a full service, just changed the fluid... But nothing is different.
I have tried cleaning the TB and I have run injector clear before. I have also replaced plugs and wires. Though I wouldnt think it would be ignition because then it would be constant and a CEL would show. And I can't see it being a fuel pump since again it would be a constant and have a CEL.
I have a few ideas, but I welcome yours too.

 

I would start looking at the throttle sensors first (accelerator pedal sensor, throttle position sensor) there are ways to test these sensors on the internet you may want to try before replacing. If the sensors appear or test well or you just replaced them and this still happens look to replace the TAC (throttle actuator control) module, its the brain that translates the signals from the pedal sensor and opens the throttle body and they are starting to go out in older GM vehicles.

and if it hasn't thrown a code yet....it will.

 

When it surges while driving, gently put your foot on the brake pedal just enough to get the brake lights to illuminate. That should disengage the lock up torque convertor. That will help you narrow it down, if the TC is the source.

 

First I heard of this, I'll try it when I get back Wednesday.