Cadillac Repair: cadilac concourse, gas tank, fuel pressure

Question
QUESTION: MY 94 CONCOURSE NORTHSTAR RECENTLY STARTED RUNNING ROUGH ,USUALLY ON IDLE ,SOMETIMES RUNS PERFECT FOR A WHILE THEN GOES BACK TOO ROUGH IDLE,ALMOST LIKE ITS NOT HITTING ON ALL CYLINDERS,THEN WILL RUN GOOD FOR A FEW DAYS.ANY IDEAS?

ANSWER: Possible faulty spark plug and or fuel injector,.


IS or HAS the check engine light ever illuminated while driving the car ?.

---------- FOLLOW-UP ----------

QUESTION: checked all the plugs and all seemed burning equal,no fouling,changed them anyway,still runs poorly and seems to be getting worse,really surges when stopped at traffic light and veryyyyyyyyyy sluggish

Answer
IS or HAS the check engine light ever illuminated while driving the car ?.

Does it run any better if the gas tank is full or does it seem to run poorly when the fuel level is low ?.

If it does, Possible condensation in gas tank. Try a can or 2 of dry gas.

Also check fuel pressure when running poorly as it could be an intermittent drop in fuel pressure due to an intermittent pump failure.