Mechanics

CHEVY RPM DROP WHEN A/C COMPRESSOR ENGAGES

2004 Chevrolet Trailblazer

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!!!
Avatar
Coordinator15
January 26, 2008.




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.

Tiny
Pear69
Jan 27, 2008.
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.

Brian 1
Jan 27, 2008.
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.
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Tiny
Pear69
Jan 27, 2008.
After checking with two other similar posts on here with Trailblazers, either 2004 or 2005, I contacted the posters directly through private message and it turns out both of their RPM flucuations are the same thing: The RPM only drops when the AC comprssor is on (any AC component engaged) and also the problem started immediatley following changing their battery. The RPM drop is not under load (it can just be in park without doing anything and as long as the AC or AC related component is on). I checked the terminals, al are connected, no corrosion, no obvious problems. The vehicle has gone well past 25 cycles of engine starts since I chaned the battery.

I also found a TSB 3116 (I believe), trailblazer/envoy stalls or RPM drop with AC running. However I can not get the full TSB with the sollution.

Tiny
Coordinator15
Jan 27, 2008.
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.

Tiny
Pear69
Jan 29, 2008.
I have a 2004 also and it was doing the EXACT same thing.

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!

Tiny
Jenncrrt
Feb 21, 2008.
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.

Tiny
Dpotter
Jun 17, 2008.
The dirty throttle body is the cause of surging after disconecting the battery. It makes sense to me since my TB has 105,000 miles on it. To help others out, this happen to me when the defroster was on. Keep in mind, difrost mode atoumaticly turns on the AC if it is warm enough out. This made it dificult tofind the cause. Would not surge or die in the colder weather. 25 degrees is the threshhold give or take a little.

TB runs great with a clean Throttle Body. It was easier to clean by removing it. Four bolds, vacuum hose and a wire conector to remove. It also helps prevent washing the grime into the monifold.

Love the internet!

Happy Trailblazing! : )

Tiny
Msm1462
Jan 12, 2010.

Tiny
Moralesmmx
Jul 15, 2010.
I know this post was created a while back but I would like to say it was extremely helpful! When the battery when out and I had to replace it the car would almost die when the A/C tried to engage. I suspected a compressor but before I contacted anyone I used the old faithful "Google" and found this thread. After multiple unsuccessful cycles I decided to purchase some throttle body cleaner. It took about 1 hour to take apart/clean and put back together. Low and behold, praise God, the problem immediately disappeared and the car runs like new!

Tiny
Ghostridermc1
Aug 14, 2010.

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