2000 grand prix gt runs and idles ruff when it warms up

i have a 2000 grand prix gt(228,699 kms) with the 3800 motor, the car has been layed up for 2 years. checked all the fluids and my find was very dirty(rusty water it looked like)in the rad, started the car up and purred like a kitten, the temp setting was just starting to come up to warm so i jumped in the car and went for a drive in a big parking lot across the street, car stilled worked fine, after a short drive to the gas station to put some new fuel in it because it was really low(had some sort of gas treatment in the tank)fired the car back up and left the gas station and car started loosing its power(about 300 ft away from the gas station), temp light came on as well. drove it straight home. car was idling very ruff. shut the car off. waited for about 2 to 3 minutes car started up fine and idled very ruff again. next day car starts fine runs for a little bit then idles and runs ruff, also if your driving it if you floor the gas pedal the revs go way down, and if you let the pedal come half way up, the revs will pick up(not very fast but it works) there is no engine light on, the only light that comes on is the temp light when it goes up to almost 1/4.

hmm...since the car was sitting so long, I'd probably give it some fresh plugs. Also change the fuel filter.

I would also flush the radiator and give it some fresh coolant, and do an oil and filter change.

That temp light worries me. Don't have my books in front of me but many cars have two temp sending units. One for the gauge and one that feeds the computer which controls the light. I have a feeling your thermostat isn't opening and your engine is overheating and that is what is causing the engine to start running rough. The gauge sensor might be close or on the radiator and the computer sensor might actually be in mounted into the water jacket. Your light is telling you there is no coolant flow through the engine causing it to overheat while the gauge sensor is telling you the radiator water is warming up just because of the radiant heat from the engine. Check to see if you see water flowing past the radiator cap to determine if the thermostat is opening.

thanks for the quick responses, i don't think there is any water moving to cool the engine from what i have sen tonight, after i got home from work i just started the car and was working fine as always but, i felt the hose going into the motor from the top side of the rad and it seems like there is no water (suppose to be antifreeze) movement at all. so i think when its nice out tomorrow, i'll take a look at draining it tomorrow, there should be a plug of some sort to drain it??? and then run to the garage for a new thermostat and antifreeze. thanks again.

You may want to flush that cooling system, and replace the thermostat. You can get a prestone flush kit at wally world for under 10.00. It hooks up to a garden hose, and usually does a pretty good job. Just be carefull to not go full pressure on the hose or you will blow hoses apart.

And to answer your question, there is a drain plug on the bottom of the drivers side of the radiator. You insert a 1/4 ratchet extension into it, turn it a bout a quarter turn and then pop it outwards.

rljt60 is right, but to clarify, on the 3800, there is one sensor at the bottom of the thermostat housing. It has independant sides, one for the guage, and one for the computer.

wally world here in canada is walmat ??? and thanks for the help! will try the flushing and thermostat tomorrow, hopefully my 13 month old will like being outside for awhile tomorrow! thanks again

yeah by wallyworld I mean wal-mart. Sorry. Good Luck!