2005 Chevolet Trailbalzer LS EXT 4.2l 6cyl Stalls at redlight sometimes

I recently bought a 2005 Chevy Trailblazer with about 129k miles on it. The vehicle is excellent condition and has no leaks on the engine or transmission. I took it for a test drive before buying for about 20min and no issues with it shift or rough idling.

After having the SUV for about a week, I noticed that it has a slight rough idle at red lights and gets a little worse when the AC is on. Twice now in the past week the SUV begins to sputter at the red light and then shuts off. It doesn’t do this every time and I have noticed it happens more when the fuel gauge is in between the quarter tank E line. My father in-law is having a similar issue with his 2003 Trailblazer, same engine and make and model.

I should also mention that no check engine light comes on or leave an ERR code.

I have read on a few forums that it could be a number of issues that I will list and please let me know your thoughts:

  1. Throttle body needs to be cleaned: We have done this on my father in-laws and didn’t fix the issue.
  2. Replaced the spark plugs: didn’t solve the issue
  3. Read that it could possibly be the APPS sensor under the gas pedal: Haven’t replaced this yet
  4. Tighten or replace gas cap: Have done this, didn’t fix
  5. Have the idle reprogrammed: Have not done yet.
  6. Could possibly be a fuel pump issue.

I have noticed this a common issue with Trailblazer and would love input. This is the family vehicle for my wife and 3 children and want to make it as safe as possible quickly.

Thanks for your time,


I don’t think it’s a fuel pump issue. If it were the opposite would happen.

The engine may idle fine when stopped, but would start to stumble and stall when power was asked from it from the lack of proper fuel pressure and volume.

I think the problem is with the electronic throttle body.

The throttle body controls the engines idle speed under all conditions.

The thing that makes me think it’s the throttle body is, you stated the idle is a little worse with AC on. That’s because the compressor for the AC is putting an extra load on the engine. And the throttle body is supposed to compensate for that extra load by bumping the idle speed up slightly.


I think Tester’s idea is correct. That’s what I’d investigate first anyway. When you say the throttle body’s been cleaned, how was that done? Was it removed from the engine and cleaned on the bench? Or was some cleaning spray just sprayed inside? Sometimes only a thorough bench cleaning will do the job. The stuff from the egr and pcv passages can gunk up the inside of a throttle body quite badly.

Besides that, I’d make sure all the routine engine maintenance is up to date. Especially if it is time for replacing the fuel filter and/or engine air filter, I’d do that along with the throttle body cleaning. You could also do an experiment of seeing if temporarily loosening the gas cap helps the problem or not. That could provide a clue. Don’t drive with the gas cap loosened though, unsafe, do that only as a temporary experiment.

I am on trailvoy.com quite often for my TB. One of the biggest things has been replacing the fuel filter every 30 k to prevent problems. At some point they switched to an in tank non replaceable filter. If you have a replaceable fuel filter do that, then move on if needed.

To clean the throttle body thoroughly, you may have to remove it and clean it on the bench