2001 Pontiac Grand Prix GT very poor fuel economy

[quote:fd37620c1e="turtle123"]2001 Pontiac Grand Prix 6 cyl Front Wheel Drive Automatic 114 km miles

My grand prix sat for two and a half years. I changed all plugs, air filter and oil, but I am only getting not even 200 kms to a tank of gas. The message center reads 12 mile to the gallon if I'm lucky. I've used fuel injector cleaner, but not helping, could it be a plugged fuel filter?. what could I do. car runs great, all the power there, just no fuel economy.
I also had a problem with security system. It would let me start car for 3 seconds and then die. (over and over). I checked all fuses ( all good), discconected battery for an hour, now I am able to drive car, but security word keeps flashing on dash.
Can somebody please give me some ideas.
Thanxs for your time.[/quote:fd37620c1e]

I am having this same problem with my 01 grand prix gt. i was told by my tech that the problem is the car's factory security system, and that it must be taken to a gm dealership to be reset. i haven't tried it yet, but am calling the dealership to get their take on it.

Air filter was number one. you should get a K&N, they last forever (just need cleaned and chargered every so often) and help with MPGs and power. Also check timing, idle speed, low tire pressure or wrong size tire (after market rims and tires can be bad for MPG and speedometor) fuel leakage, clogged injectors, proble in fuel injection system