Service Engine Light - Poor performance

[Black GT]

I have a 98 grand prix GT that I have owned for about a year and has 55K on it now. SES light was comming on about 25% of the time for the last two months (no deterioration in performace). Then two weeks ago it came on full time and gas mileage dropped 15-20%. The first problem is that if I fill it with gas, the car runs extremely rough for about 1-2 min (i assume because I removed the gas cap). Also in the morning when it is cold, it will start fine, but will stall after running for 2-3 min, then run fine for the rest of the day.
Because the SES light is on I assume my problems are the O2 sensor, but is there anyway I can check the computer codes myself to verify this before I start dumping money into sensors I don't need?
Does anyone know why the engine woud run like crap just becase the gas cap is removed?

Thanks in advance..

[The Burning Rom]

Never assume it's the o2 sensor. It could be any number of things. Take your car to autozone (or some other automotive store) and have the codes scanned. Or find someone with a scanner. Find out the code..and what it means before you buy any parts.

[Black GT]

Was afraid that was my only choice. Is there a reference list that has all the codes? I would like to have that info before I fo in..

Thanks

[BryantGTP]

The SES light combined with sluggish performance means you have a cylinder misfiring. Getit scanned at autozone if you don't own a scanner. Probably just fowled out a plug.

Check the OBDII site for the codes, search around, there's tons of good info available:

http://www.obdii.com/codes.html

hope that helps!

-Andrew

[Black GT]

OK - went to Autozone and got it scanned code was P1441 I believe. Turns out that is "purge system" error. Purge system is in the gas tank and part of the emmission system, and will turn the SES on. Parts for the purge sustem (cannister, solonoid, valve) total $150.00 Before I plopped down my hard earnd cash I started asking questions on why it failed. It turns out that I did it to myself. I drive at least 80 miles a day so the less I'm at a gas station the better, so I ALWAYS top off the tank - every drop I can put into it. Doing this can damage the purge system because excess gas can get into a vent tube and go into the valve and cannister causing failure. Fortunately in my case, no damage was done. After correcting my ways and a $7.00 gas cap (the seal was bad on the old one), the SES light is still out after 3 days of operation. BTW - don't overfill...

[BryantGTP]

Originally Posted by Black GT

I drive at least 80 miles a day so the less I'm at a gas station the better, so I ALWAYS top off the tank - every drop I can put into it. Doing this can damage the purge system because excess gas can get into a vent tube and go into the valve and cannister causing failure.

You completly sure on this? I gotta be more careful then. I drive 600 miles a week and always drive full to empty, then top it off.

[Ripn12s]

I think that bad gas cap was your problem. It's been posted before on clubgp. I remember one guy failed inspection becuase of it and the shop tried getting him to buy alot of expensive parts and all he did was replace cap and passed.