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2004 Grand Prix poor mpg

R

robf270

New member
Could a coolant temperature sensor cause poor gas mileage? The reason I'm asking is because my wife's car took a lot longer to warm up this morning. It was about 52 degrees this morning. And the gauge on the dash didn't get half way between the 1/4 and 1/2 marks. And I travel about 30 miles to get to work. And I also notice the average mpg went down on highway to 20.4 when it was warm outside it would say about 27 to 30. We have been chasing the poor mpg for a couple of months now. Everything has been changed from basic tune-up to new o2 sensors and new converter. Running ngk iridium plugs and 8mm wires. Any help would be appreciated. And we are getting between 10 to 15 city driving
 
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Yep. If it's reporting too cold a temp to the PCM it could be letting it run rich. Have you cleaned the MAF and throttle body (the inside of it) as well? Checked for vac. leaks?
 
I did clean the MAF when I changed the air filter. But not the throttle body. Should I take the throttle body off and clean it or leave it on? No vac leaks
 
In that time it should have warmed up. Maybe you need a new thermostat?

If you have the time, cleaning the throttle body would be a good idea. You'll need to scrub pretty good.
 
I'd replace the thermostat to make sure it isn't sticking open since it's cheap insurance anyways, and if that doesn't help test the temperature sensor. If you have a multimeter you can test the resistance at certain temperatures. I believe at 40 C (104 F) it should read around 1400 ohms, so figure a higher reading when it's sitting at room temperature. The resistance lowers as the temperature increases.
 


robf270 said:
I did clean the MAF when I changed the air filter. But not the throttle body. Should I take the throttle body off and clean it or leave it on? No vac leaks
Click to expand...

Best would be to remove the entire TB and clean it. The junk mostly accumulates on the backside (engine side) of the blade.
 
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