Stalling Car

My fiancee received a 1994 Pontiac Bonneville from her grandparents. We were told that it was well maintained and that there were no problems with it. However, in the last few months the car has been stalling while warming up or shortly after taking off. We had it serviced at her family’s trusted mechanic, but they couldn’t find anything wrong with it, even though the “service engine soon” light kept coming on, even after they turned it off. Now, when the car is warming up, instead of running low on rpms, struggling, and stalling, the car will shake when it goes into the low rpms and then accelerate on its own, sometimes up to 3000 rpms. Eventually, it stalls anyway. While the engine revs up and down rapidly for the first few minutes, it starts to settle down after about five minutes. She doesn’t feel safe driving it until it stops shaking and is completely warmed up after ten minutes. Is this fixable, or should we find a new car?

That car needs to be hooked up to an analyzer to find out what is wrong. It should have a code since the check engine light is on. Does the “Trusted mechanic” have an analyzer? Should be simple to figure out. Whether it will be a cheap fix is a good question.