I have an 06 H3 with 230k miles on the odometer but engine replace at 160k and trans replace at 220k. The engine surges when accelerating but only when A/C is on. It settles down when it gets to cruising speed in 4th. Any thoughts?

 

The pcm increases rpms when the ac compressor kicks in. Same when you're driving with cruise control set and enter an incline, the rpms will increase.

 

I understand that the rpm’s will increase when the compressor kicks in but this isn’t just an increase in rpm’s. It is a up and down, rhythmic surge until I get to my cruising speed then the surging goes away.

 

"Stumble"
What is engine stumble?
Hesitation is when your engine misfires, stumbles or lacks power when you accelerate or step on the throttle. The problem often means the air/fuel mixture is not being properly enriched or is going lean, or the ignition system is weak and is misfiring when the engine comes under load or the air/fuel mixture goes lean.

 

Easy/cheap stuff first: Using a quality scanner, check for active/history codes. Check/replace air filter, check/clean maf sensor, check/clean tb, ONLY use top tier gas.

 

Which............ can 100% be caused by a dirty TB. Your PCM calls for additional throttle because you turned on the AC, the TB is dirty, cruddy, sticks, does not respond smoothly as it should, hence the PCM is calling for throttle position (TP) increase, it lags, PCM calls for more TP, now it over corrects and the PCM then calls for reduced TP, it lags, and then leads to too much reduction. Etc......... until you get to a steady TP demand at cruising speed.

TB cleaning should be done about every 30K miles, more often in dirty dusty conditions. Basic modern vehicle maintenance.

 

Thanks Doc. Your reply is very helpful. I hesitate to use forums like this because you get a different answer from every reply and it tends to confuse the issue. Don’t get me wrong, I think this forum is helpful…if you love to tinker with your Hummer and have a sound basis in vehicle mechanics. I’m not one of those people. To be honest, I hate working on vehicles.

Thank You again.

 

Removed and cleaned the throttle body this morning. There was no change in the symptoms. Any other suggestions?

 

Hopefully you used Throttle Body Cleaner to do that job?

Have you cleaned the MAF yet?

 

CAI was my first go to with the OP's symptoms. Still waiting for any possible codes?