95 prizm guzzling gas and dies when decelerating or stopped

The car has had a tune up (oil filter, air filter, spark plugs, wires) 5 months ago. 7 months ago i was getting 420 miles a tank; 6 months ago i started getting 160 miles a tank all the sudden. In addition to poor gas mileage the car idles poorly when decelerating or when stopped; often times it dies all together. It does this all the time, whether it be hot, cold, humid, or dry. It seems to happen in all weather conditions and when the engine is both hot and cold. Any suggestions would be appreciated since the mechanics i've taken it to have had NO idea because their computers didn't tell them the problem and I'm just a girl that can't explain what's wrong with my own car... Anyway thanks a ton.

just wondering is it a 5 speed manual or an automatic. Chances are if it is an automatic it might be the tourqe conveter clutch locked up. Or if it isn't that it might be the idle air control. This allows for a small mount of air to enter into the engine while the throttle body is closed. Also it allows the engine it increse the speed of the motor while warm up or during decell. Just a few questions..... When you start the car up after letting it sit for a while (so that the engine is completely cooled down) dol you have to give it a little bit of throttle to allow it to start? Does the car feel as if it is lacking power while during accel? Also could you list any unsually things that happens while driving or starting the car, if possible a little more detail the listed.

Chris

when it's been sitting it starts and runs fine for about 1 minute. it's a manual transmission. It smells like fuel sometimes while i'm driving. It lacks power when accelerating compared to when it was running well, but it's not so much of a power loss to notice. As for any other unusual things, that's everything I've noticed. Guzzling gas, stalling, dies when stopped or decelerated, smells of gas sometimes. Sorry i can't think of anything else for you to go on. Thanks for responding:)

It might be a stuck open injector. Thats the only thing I can think of