Coolant temperature sensor pegged over 260?

AWARNER

MEMBER
2002 PONTIAC GRAND PRIX
3.1L
6 CYL
2WD
AUTOMATIC
190,000 MILES

Coolant temperature is maxed out passed 260 after installing a bad ECT sensor. Car idles too low to keep car running. Then replace with a new one and has always been maxed out past 260 since then. While trying to find a short with the ground that is shared between MAP and coolant sensor, took off throttle body to get to ECT easier. Unplugged ECM trying to chase the wire put back together and now my car wont idle without giving little throttle. How long until the ECM relearns idle speeds ECT?

5 Replies

JACOBANDNICKOLAS

MECHANIC
108,300 POSTS

Hi,

It shouldn't need more than a few short trips. Since you had the throttle body off, are you sure there are no engine vacuum leaks? That will cause it to not idle.

Here is a link that shows how to check for engine vacuum leaks:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Let me know.

Joe

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Friday, August 27th, 2021 AT 10:58 PM

AWARNER

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5 POSTS

Yes, no vacuum leaks repair all that was found with brake cleaner. That's what I thought too, as I was looking online and found no actual answer but figured I'd ask someone on here, but it has been a lot of trips long and short. IAC valve been cleaned etc. But would it matter that I unplugged the ECM and it deleted all fuel trim codes and whatever else ECM holds like I don't have the power it used to have before hand. Do y9ou know what would cause a high RPM misfire, causing it chug?

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Monday, August 30th, 2021 AT 1:04 AM

JACOBANDNICKOLAS

MECHANIC
108,300 POSTS

As far as disconnecting the ECM, it will relearn everything within a few miles. If you have taken trips, that information should be saved again.

Now, a loss of power, high RPMs, and chugging can be a few things. Have you checked fuel pressure? If it is off (too high or low) it can cause this. Is there any smoke from the exhaust? Have you scanned for codes now? Does the exhaust have an odd smell or sound to it?

Let me know.

Joe

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Monday, August 30th, 2021 AT 5:24 PM

AWARNER

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Without doing a idle relearn procedure? Does Pontiac have one for the lg8 engine? But yes ran codes and the only one that's came up since I unhooked the ECM, was idle to low, looked it up online and just said to do idle relearn. Probably did 5 or 6 different ones different cars. But no I haven't checked fuel pressure I will do that tomorrow when I have light. No smoke at start up or when hard acceleration, I bought the car maybe year ago and 3 months after had to replace the catalytic converter due to being clogged, it doesn't feel like that. Also replaced fuel filter honestly not super long ago with miles or time but could it be plugged again? What should fuel pressure be at idle and do I test it with RPMs up to?

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Monday, August 30th, 2021 AT 9:51 PM

JACOBANDNICKOLAS

MECHANIC
108,300 POSTS

Hi,

On this vehicle, the IAC (relearn) should be done automatically by the PCM by simply turning the key to the run position and then off. See pic 1 below.

The remaining pics are diagnostic for the IAC. Take a look through them to see if they help.

As far as fuel pressure, the last pic below shows the manufacturer's specs. Here is a link that explains in general how to check the pressure:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Let me know what you find or if you have other questions. Also, let me know the specific code you are getting.

Take care,

Joe

See pics below.

Images (Click to make bigger)