random miss fire codes po300 & po306
my 96 blazer keeps getting the above codes at least once or twice a week.
engline light pops on after driving a few miles. usually happens on the same stretch of road in the am while driving to work. engine will miss,stumble and run badly for about 10 seconds setting the engine light on and 30 seconds later all is well. complete tuneup done(plugs,cap,rotor,etc) 3 weeks ago.also might add that i was getting about 200-240 miles per tank of gas.now i'm lucky to make 160-180 miles per tank.other than the issues as explained the truck runs fine and has good power.i realize there are some consessions to be made for the truck being 180,000 miles old,but what could be causing the random miss fires. besides the tuneup i have replaced in the last 6-8 months
fuel pump,egr,mass air flow,spider injection system,ckp sensor and map sensor.