Pontiac Sunfire gas mileage

[kaykeewhoa]

I have a 2001 Pontiac Sunfire, 4 cylinder automatic. I have been getting around 12 miles to the gallon when I should be getting 20-25. The transmission is also stubborn..it has trouble shifting into first gear and goes up to 4 rpms to accelerate at a normal rate, does this have anything to do with the mileage? any ideas why this is happening?

[Mr T]

How many miles on the car?
Transmission problems can definatly kill your milage, but other problems can give similar symptoms.
Does it shift hard or rough? (loud thud when it shifts?)
Does the engine idle rough?
Does it feel weak when you are accellerating?
Have you ever noticed the engine speed (RPMS) go up when you take off, bu tthe car doesnt move?
Shift into all gears while stopped, do you have trouble getting into any? Does it jerk or make a louder noise when you go into any gears.
While driving, does it shift into all gears? (probably a 4 speed, but you will hear 4 shifts (into 2nd, into 3rd, into 4th, into final drive) Does it go through all gears? (last shift may be hard to feel, watch your tach) WHile cruising at a constant speed, pushing the pedal down further whould get you back into 4th, pushing further should make it downshift into 3rd, and it should go back into 4th, then to final drive once you let up on the pedal a bit.

Follow the procedure in your manual and check your transmission fluid. (It is not like your oil, you have to do certain things first (usualy warm the engine, park on a level surface, shift into all gears for a few seconds each, and check with engine running) If you dont follow the instructions, you will get a false reading. You need to check your fluid level, and condition. Check for a burnt smell, or a very dark red color. Transmission fluid has a unique smell, and is usually pinkish red in color. (Pull the tranny dipstick on another car for comparison). If its low, add and test(damage may have already been done), if its burnt or very very dark color, time for service, be prepared for a expensive bill. If you have many miles on it (check your manual for the change interval), it could be 'worn'. THis can quickly damage your trannie though. GM's are usually solid trannies but sensitive to poor fluid conditions. Find a trusted shop.

If that all looks good, check the rest of your engine out. There could be something there.

[kaykeewhoa]

There are about 59,000 miles on the car. The only gear it has trouble shifting into (its an automatic) is second. The car has no trouble when its idling or when it's shifting into any gears past second, and it does shift all the way from 1st to drive. When I accelerate into second, the car is very stubborn and I really have to step on the gas to accelerate at a normal rate, and the RPMs go up to 4, way past what it should be going up to as far as I know. It gets very loud until it finally shifts, and past that acceleration is normal. Think this is affecting the mileage? Someone recommended I replace the Oxygen sensor...

[Mr T]

If you get on the gas to make it go, it will accellerate higher before shifting, 4000rpms is normal for shifting with your foot down harder (the computer is looking at your pedal, not the engine in this case). Dont worry about the high shfit point.

What is your transmission fluid change interval??

You still need to check your transmission fluid by the procedure in your manual. How is it?

O2 sensors often throw codes (check engine light) when the fail and/or would give more consistant problems. Your milage is kinda low for this. You have 2 in the car and they can be expensive. Has yoru check engine light been on? Autozone will read your codes for free.

You should also check stuff like your air filter, PCV valve. Pull your plugs and look at them and check gap. Make sure they are within spec. (plug gap should be on your emmisions label, usually on the underside of your hood or a shock tower) If it's off or the tips are worn, replace. 100k miles is under "lab" conditions. Make sure your plug wires are in good condition. Does your gas pedal stick the first time you push it when you start yoru car? Common GM problem when your intake gets all gummed up. That can effect your performance if it gets bad enough.

let us know the above and we'll recomend from there.

[kaykeewhoa]

thank you. I will do all this and let you know...as soon as the snow quits!