I own a 1991 pontiac firefly 1.0L, 3 cyl, auto transmission. The car runs great when cool or just starting up. When its up to temperature and in either drive or reverse it idles very sluggish and the rpms are way down. It doesnt matter what the weather conditions are outside. It stalls only sometimes but the car shakes pretty bad. In neutral or in park the car is a bit better but still a little rough. Its had a full tune-up including cap, rotor, wires, plugs, fuel filter, air filter, pcv valve but it was doing this before the tune up. Its progressively been getting worse. Oh, it burns a little bit of oil as well, im not sure if that could have anything to do with it. about a quart every 1500-2000 miles. I appreciate anyones advice or input on the problem, id like to ry to fix it myself.

 

i would say your pistons are firing incorrectly, meaning the timing is off. its a bit of an annoying fix, you have to re-time each of your pistons, you might want to get it proffesionally done seeing as it has to be perfect. As far as you burning oil, your piston rings probably arent sealing, which leads to oil leaking into the top part of the cylinder and being burnt up by the firing of the pistons. This cant always be fixed by simply replacing the piston rings, the walls of your cylinders might need to be re-honed. 3 cylinder engines are known for firing issues.