[coachchuck]

I bought a 1990 Grand Prix LE 3.1 a few weeks ago. The car had been sitting for 2 years. The man I bought it from said it was his wife's car and she passed away and he hasn't driven it since. Of course the battery was dead so I bought a new one. Drove the car, it ran fine. I noticed immediately that the gas light and temp light were lit for no reason. Every now and then the lights go off, but soon return. Gas gauge showed 1/2 tank of gas and temp gauge read fine. I went ahead and changed the fuel filter and t-stat and filled it up with gas. The speedometer reads 80 when you are going 40. The odometer read 80945. I have driven the car about 200 miles and it has only moved 8 miles. Trip doesn't move at all. The car drives perfectly one day, the next it stalls upon stopping or turning. It has even stalled driving 45 mph. Sometimes you crank it up and the idle is very high. You can get up to 55 w/o even pushing the accelerator. I check codes and the only one I get is a 51. One book says that it is the PROM and one book says it's the ECM. I have no idea which one to replace and can this cause all of the other problems?