Why might the engine on a Pontiac Transport run rough?

Answer 1

There is probably a vacuum leak somewhere. Check the rubber boot where the pcv valve attaches. Check the hoses for cracks. Check where the hard plastic from the body lines connect to a rubber boot under the alternator, as these can unplug easily.

Could also be coil pack, spark plugs and wires.

A cracked mount, or incorrect gasket on the EGR valve leads to a VERY rough engine. The mount can be damage by the battery during replacement. And fixing the mount can lead to an incorect gasket being appied.

There are alot of sensors on a transport. I had a problem were when we pull out onto road the car would stall, that's was repaired by a throttle posisition sensor, now when we traveling at highway speed or at 25 or 35 mph the car would act like you turn-off the key a computer diagnostic said it is the cam position sensor so before you spend alot of dough replacing sensors first look to see if there not ub=nplugged then try to a computer diagnosis usally a Auto Zone or Discount uto will do it for free. that's were i would start but for a rough idle for 2.00 bucks try a gas-dry that's always works for a rough idle especially if you buy gas in Burr Oak , Michigan pop. 300