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Repair guides and support for Saturn's 2nd generation SC, SL, and SW.

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High idle and poor mpg

My car randomly idles pretty high (around 2000 rpm) and I've noticed my mpg has suffered. I only got about 250 miles out of a tank of fuel. I like to think I drive pretty sensibly. I had the check engine light scanned and it came back with evap system small leak p0442 and catalyst system low efficiency bank 1 p0420. At the top of the printout for the engine light it says "ASE certified mechanics have seen this issue on your type of vehicle and the most likely solution is replace fuel tank pressure sensor.

I was ready to do this but I was told that the fuel tank pressure sensor doesn't affect how the engine is running.

Could the idle and poor mpg be the sensor? A vacuum leak? Something else? The car otherwise is strong and has no knocks ticks or other issues shy of a broken exhaust hanger.

Please help.

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UPDATE - I checked and do need a new catalytic converter. I cangrd the plugs and plug wires also to help out since they were showing obvious wear. Also what I thought was the car over heating is the cars normal operating range and the fan is now kicking in like it's supposed to after changing the ects (engine coolant temp sensor). I was unaware of the areas that sensor was able to affect but it made a difference in my idle and not also. after some research on forums and Google the sensor and plugs/wires helped alot and when I have enough cash I will be changing the catalytic converter. Thanks for the guidance!


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@dustinrulo1988 the P0420 code actually has numerous causes of which all of them could be the cause of your symptoms:

Fuel injectors may be faulty

Fuel injector leaks

Spark plugs may be faulty

Improper ignition timing

Powertrain Control Module (PCM)

Three way catalyst converter Bank 1

Intake air leaks

So, I'd start with the easy one, which would be your plugs and checking for air intake leaks. Most common issue is a failing catalytic converter. Also, you do want to check your O2 sensors and see if they need to be replaced.

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Dustin rulo zal eeuwig dankbaar zijn.

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