having problem keeping 1990 chevy lumina running,starts real rough(coughing,sputtering)than after warming for 10-15 minutes smoothes out,but,will only go about 6miles than suddenly loses RPM'S..and just stops,..had fuel filter replaced,added gas treatment,added high octane gas ..still no good..local garage says "junk it" help..says may be sensor but unable tell which one..any suggestions gratefully accepted

 

Start with my "The Basics" post below.

 

Doris,
If your local garage can't offer a better explaination than that, it may be time to find a better local garage. Are you getting a check engine light while the engine is acting up? Check engine light or not, any reputable mechanic should be able to hook the car up to a scan tool, drive the car, and get some idea of what's going on.

 

has the car had a tuneup? has the catalytic converter been checked?