My 89 Sunbird (2.0L TBI) suddenly developed problems that looked like a MAP sensor. I measured the voltage and found that it was not dropping as the engine is accelerated. I replaced the MAP sensor with a brand-new one and the condition is the same. There seems to be plenty of vaccum with no leaks and when the line is connected to the MAP sensor, it doesn't have much affect. (The voltage remains higher than 4V and does not drop). Has anyone out there seen a problem like this? The engine is backfiring thru the throttle body and I am wondering if it jumped out of time. It's really fouling up the plugs with carbon. It was running great just before this happened The engine runs but will not idle. For some time before this occured, it was taking longer and longer to get it started. If I started it during the same day, it would start fine. If it set for several days, it would turn over and over before firing.