2004 Chevy Trailblazer RPM drop when A/C compressor engages

coordinator15 · Posted at Sat Jan 26, 2008 6:52 pm

Electrical problem
2004 Chevy Trailblazer 6 cyl Two Wheel Drive Automatic 65,294 miles
----------------------------------------------------------------
I have a 2004 Chevy Trailblazer which has ben great withnormal maintenance. My bettery was hard hard cranking and needed to be replace, so I stopped by the local parts store and bought a new battery last weekend and replaced my battery.

Here is where the problem started, that night after changing my battery, I went to use the defroster. When the A/C compressor engases at idle in park or neautral every 5 to 10 seconds the idel drops and will either almost stall the engine or occassionally does stall the engine. This happens in drive as well, and when driving, since the RPM drop and come back up, the vehicle surges at low speeds. The RPM drop only occurs when any A/C component is on (A/C, defroster, or re-circulation), when just the vent is on, the RPM does not drop and the engine run fines.

I saw another person posted with the exact same question on your site, with the exact same make and model vehicle and approximately same milage but I could not find an answer (see link to the other question: http://www.2carpros.com/forum/a-c-and-electrick-vt66495.html )

Please help me with this question, it seems like this is not a one of a kind problem.

Thank you in advance!!!

pear69 · Posted at Sun Jan 27, 2008 4:09 am

Sometimes when you disconnect the battery the engine must go through 25 running cycles to reboot the computer. OR your IAC valve may be failing. Be sure your battery connections are tight and clean.

brian 1 · Posted at Sun Jan 27, 2008 3:16 pm

might want to try this.found bulletin #1878920. Engine Stalls When Air Conditioning Is Turned On At Idle - keywords HVAC rough condition CJ2 CJ3 surge. Engine may stall with the air-conditioner on and or while adding additional loads to the engine at idle. An example of an addition load would be turning the steering wheel left or right with the air-conditioning on. This type of stall usually occurs during idle or slow parking lot maneuvers. This concern may not set any diagnostic trouble codes.

Clean the throttle body bore and the throttle valve plate using a clean shop towel with GM top engine cleaner, GM P/N 1052626 (Canadian P/N 993026) or AC-Delco Carburetor Tune-Up Conditioner, P/N X66-P, or an equivalent product.

pear69 · Posted at Sun Jan 27, 2008 5:21 pm

Do not go looking for problems that did not exist before you changed the battery. You say the trailblazer is well maintained--I dought that a dirty throttle body is the problem because the problem started after you changed the battery. This problem is most likely electrical in nature.

coordinator15 · Posted at Sun Jan 27, 2008 8:18 pm

pear69 · Posted at Mon Jan 28, 2008 11:03 pm

When you turn on the A/C, the A/C compressor kicks in. This puts a small load on the engine. The RPMs should go down a little. However, when you disconnected the battery, all the sensors that compensate for this load- lost power. The IAC valve can very easily cause the problem you describe and may need to be reset. To do this follow the following--1: disconnect and remove the IAC valve. 2: measure the distance from the tip of the pintle to the mounting flange. It should be 1 and 1/8 of an inch, if not push the pintle in so it is. 3: re-install the valve. 4: cycle the key on for 10 seconds and off for 10 seconds. This resets the valve. 5: Start the engine (do not press the gas) and let it idle for 5 minutes, then shut it off for 30 seconds. Then start the engine again and drive around for a while and test the A/C. During all these steps do not turn on the A/C until driving around during step 5. Let me know how you make out..
BTW: the IAC valve is the idle air control valve. This valve controls the amount of air allowed to bypass the throttle plate when the throttle plate is closed or at an idle position--not necessarily at engine idle--it's at throttle position idle.

jenncrrt · Posted at Thu Feb 21, 2008 1:22 pm

I have a 2004 also and it was doing the EXACT same thing. I found this ... http://wiki.answers.com/Q/2004_trailblazer_with_105000_miles_when_stopped_and_idling_with_ac_on_the_rpms_cycle_down_and_up_the_truck_dies_but_will_start_right_back_up_the_ac_is_working_fine_happened_after_replacing_battery

Sure enough, cleaned the throttle body and problem solved!! I also read elsewhere that this is caused from not using "top tier" gas. (ex. Shell, Cheveron) I have always used Walmart, or Sam's. I have joined the trailvoy forum! It is a great site. Has anything you would ever want to know about Trailblazers from other owners. Browsed this site before I found it and thought I would share!

dpotter · Posted at Tue Jun 17, 2008 4:20 pm

your problem is a dirty throttle body. Had the same same happen after changing the battery. A good friend sells chevys and asked the service manager to confirm what I found on line. Over time the car's computer adjusts for driving conditions, engine wear and ect.... with a dirty throttle body (which is normal) the computer adjusts. When the battery is changed, it re sets to factory settings. So the computer thinks you have a brand new vehicle, with a clean throttle body and regulates fuel/air to that. so it stalls when anextra load is applied. A two doller can of carb cleaner and about 20 minutes will fix u right up. I'm so sick and tired of people on here spouting off with what they think is the answer. I had no clue till i started looking on line. 20 years ago would have been out at least 500 bones at the dealer for this. For all it's fualts, the internet is a god send.