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Changed the thermostat, now the car doesn't run properly

Hi all,

I have a 2005 Pontiac Aztek. My brother in law recently replaced the thermostat and for whatever reason, messed around with the sensors. Now, when you start the car, you have to hold the gas pedal down a little bit, else it dies. When it does run, it backfires through the intake, runs rough, and revs up to around 3000 rpm on its own.

We’ve tried checking the fuses, resetting the computer and cleared all the codes, yet nothing seems to be working.

Any ideas on what to do?



What were the codes you cleared. Did you address the code before clearing them?

Can you please tell us what sensors you’re referring to?

And what do you mean with “messed around” . . . ?!

My wife took it to Advance Auto to have the codes checked. There was an SES light which they said was probably due to a faulty O2 sensor but they told us the car should still run okay and we can get it fixed whenever.

There was an ABS and brake light on as well but we’ve had our brakes checked and nothing was wrong.

I wasn’t out there with him when he replaced the thermostat but he said that he unplugged some of the sensors. I don’t know if he did this to help reach the thermostat housing or what. It’s not easily accessible like on some other cars.

When we started the car back up, it immediately revved on its own, backfired and died.

That’s what I meant when I said he “messed around” with them.

We need the actual numbers, not the vague explanation the knuckle dragging counter guys at AZ told you. In the form “P0123”

My guess is Bro-in-Law forgot to reattach a wire or 2 and now the car won’t run. Stop letting him touch the car, take it to a real mechanic to get it diagnosed.

Sounds like a vacuum leak.

He could not plug a wire into the wrong sensor. Most plugs are made that you cannot do that, as each is a little different.

I would look at the vacuum hoses. He may have unplugged one, or accidently knocked one off in the process of installing the thermostat.
Also…these hoses are 13 years old and vacuum hoses can get brittle and just bumping one can open a crack in one .