Rough Idle and bad gas mileage - Maintenance and Repair Forum

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Rough Idle and bad gas mileage
Friday, February 18, 2005 1:30 AM
So I just got my 2000 Sunfire GT with the 2.4 recently and it seems I'm getting pretty horrible gas mileage compared to some of you members. I've been getting like 300 to 330 kilometers per tank consistently. The car is not throwing any codes and the only symptom I have is kind of a rough idle. Just put new plugs (AC Delco) and a new air filter with no luck. The car has about 100k on it. From what I have read the 02 sensor could be a likely culprit but I was wondering if anyone else had any other ideas or suggestions?

Re: Rough Idle and bad gas mileage
Friday, February 18, 2005 1:34 AM
Oh yeah, it can be a little tough to start sometimes too, not really bad but just not very smooth if that helps!
Re: Rough Idle and bad gas mileage
Saturday, February 19, 2005 9:05 AM
could be many things especially with that type of mileage ill put out a list here for you

1. Run some seafoam through it cleans out alot of nasty junk
2. Injector Cleaner
3. Replace 02 Sensors
4. Replace fuel filter
5. Check for vacum leaks (this almost always contributes to rough idle) also the vacum lines control fuel pressure if leaking will cause a higher fuel pressure therefore less gas mileage
6. Check that the throttle body is torqued down ok and intake manifold is not leaking maybe even replace the gasket
7. Replace coil packs and spark boot springs

If it isnt any of that well I wouldnt know what to tell you




1989 Turbo Trans Am #82, 2007 Cobalt SS G85





Re: Rough Idle and bad gas mileage
Saturday, February 19, 2005 7:42 PM
Rodimus suspects the fuel injectors. I agree, and his treatment would be the first

thing to try.
Re: Rough Idle and bad gas mileage
Saturday, February 19, 2005 10:29 PM
Awesome, I'll definitely run down the list and check all those things out. Thanks for the advice guys...
Re: Rough Idle and bad gas mileage
Saturday, February 19, 2005 11:04 PM
How much is a fuel filter anyway? and is it easy to change?
Re: Rough Idle and bad gas mileage
Saturday, February 19, 2005 11:05 PM
Oh yeah, Where would I go to get new boots, springs and coil packs for a 2.4 L cavy?
Re: Rough Idle and bad gas mileage
Sunday, February 20, 2005 8:04 AM
The fuel filter you can pick up at any auto parts store for like 12 bucks and while your there pick up a haynes manual has the instructions on how to replace the fuel filter alot of shops will charge like 50 bucks to do it and really you would be surprised how easy it is. It took me longer to jack up my car than it did to replace it but I'll try to describe it here.

1. Jack up the rear end enough you can get to the rear suspension and go under from the rear end in the middle of where the rear "axle" (we dont really have one but play along) would be , and take off your gas cap, this depressurizes your system (thats a good thing)

2.you will see where the old one is little canister looking thingy with a clip on one end and a bolt fitting on the other. Dont really matter which end comes off first. Now this is VERY important and if you never done it pay attention. When you loosen the fitting fuel will come out, keep your head as far away as possible, and when it starts to come out back up and let it drain a little dont want to be splashed in the eye with fuel, but you will smell like gas by the time your done anyway.

3. Then take off the other fitting there will be some more fuel sprinkling so be careful, and please DONT SMOKE WHILE DOING THIS

4. Now that the old one is off put the two fittings on the new one, lower the car, and put your gas cap back on

5. Put the key in the ignition and turn foward to the on position but dont start it, check for leaks, turn it off, repeat the process 3 times, if leaking check your connections, if not your done

For new boots you can get them at a dealer or a junkyard , not sure if auto parts stores will have them some may



1989 Turbo Trans Am #82, 2007 Cobalt SS G85





Re: Rough Idle and bad gas mileage
Sunday, February 20, 2005 11:23 AM
when changing the fuel filter you might need a tool to disconnect the lines i had the tool and it wouldnt work so i just pulled them a part and bent the tabs back



Re: Rough Idle and bad gas mileage
Sunday, February 20, 2005 4:07 PM
all you should need is a flat head screwdriver for the clip



1989 Turbo Trans Am #82, 2007 Cobalt SS G85





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