the car in question is a 1993 pontiac grand prix. the engine is 3.1L V6 with four speed auto the car has 166,000 miles. My question is this, my car will perform much better in cold weather than in hot weather l will have better acceleration and better throttle response in cold weather but in hot weather the car will defiantly be slower. is this becasue its an OBD1 car?. The reason why I am thinking that the map sensor is going bad is because the map sensor reads how dense the air is inside the intake manifold and if the sensor is going bad than this will make the car run very different in hot and cold weather right?. the car does not have any trouble codes when l hook up the scan tool and my engine light is not on. But l heard that OBD1 computers will continue to use info from a sensor that is going bad but it will not throw a check engine light if the sensor completely fails is this true?.
My gets 260 miles to a tank if l just drive around town. the car will get over 300 miles with mixed highway and city driving and over 400 miles with mostly high way and a little city driving.

u must be really mechanically inclined,you gave such a good line of fact's. but u really did not ask a question. i'm bettin all u have is a lean surge,usually when cold. TPS (THROTTLE POSITION SENSOR) MAP SENSOR (CTS)IAT USED FOR LTFT(LONG TERM FUEL TRIM) EVEN THE 02 SENSOR. FUEL INJ. SERV. PCV SYS. little comb is of 2 or more etc.lab scope needed to go further! But all in all ur car probally is performing good & ur not a lead foot! also map sensors that r bad(check vac line/sorce) make eng. run lean(lean surge) diff. bet. block learn +128 & interegrator + or - 3 STFT/LTFT etc.anytime u can get 28 mpg+ hwy is nothing to snease at! with a 3.1 v6 pushrod motor. by the way this F.I. set-up is known as a SPEED DENSITY sys. l do belive u have just FIXED ur little ideosyncritcy

Check the fuel pump for pressure 50-60 psi running.