Pontiac Repair: Car stalls out after getting to temp, coolant temp, pontiac grand prix

Question
I have a 1991 pontiac grand prix se with a 3.1 engine. My problem is that my car idles really rough and stalls out when engine is at normal operating temp. Thought it seemed like a vacum leak and checked all hoses. replaced upper intake plenum seal which was leaking but still same problem. having my foot on the brake seems to make it idle worse and stall quicker so thought maybe was brake booster. unhooked hose from booster and plugged it up, checked for leaks but still same problem. replaced coolant temp sensor, still same problem. I don't know what else to do.

Answer
Hi Rishid:

These cars were noted for rough idle and stalling conditions. the first thing I'll ask is if the battery was replaced recently or died prior to this happening if the answer is yes then Google 3.1 liter idle learn for that year car. there is a long drawn out proceedure to make the engine computer learn the idle speed for that car. Before you do the learn do 2 things clean the throttle plate ands throttle body. They get all carboned up over time and disconnect the battery and let it fit for a few miuntes and touch the cable ends together while they are diconnected from the battery. If that is not the case then I would look at possable a bad injector or 2. that engine is VERY touchey if you have a injector that the resistance is skewed. take the top manifold off again and measure the resistance of each injector I memory serves me right they should ohm out about 11 ohms with a cold engine. if you have one or more that are much higher or much lower then change the ones thar are hi or low in resistance. Good luck :)