Geo Prizm driveability problem

[EMD Diesel Power]

Hello,



My mom's '93 Geo Prizm has had distributor cap, rotor, plug wires replaced and it still has a misfire or a stumble at road speed (45-60mph). It also develops a rough idle. None of this happens with a stone-cold engine... . after about 10 miles it will act up and do the symptoms mentioned above.



Dealer originally diagnosed it as moisture intrusion into the cap (I saw the cap... it had evidence of water intrusion).



They have replaced the battery (found it to be going bad) and also flushed fuel injectors (dealer paid for it, as it didnt correct problem).



anybody out there have any ideas, suggestions as to what the problem could be?



Further details on the car... . 1993 Geo Prizm 1. 6L L4 engine with a 5 speed manual. 113k miles on it.



Thanks in advance.

 

[LSMITH]

I have had coils do what you describe, you can cool them with water and see if it goes away. SHUT IT OFF before you wet it, if it has a current leak you will get POPPED if you don't. Also would be wise to drive down the road until it misses then go home to test the cooling theory in case the coil is not sealed well and needs to dry out. Cool it slowly and see what shakes out.



Another thing to check out is to remove the gas cap when it starts to stumble, if the vent does not work correctly it can airlock the fuel system and starve the engine of fuel. A hot fuel pump lowering rail pressure will also do it, but is not very common and the dealer should have checked rail pressure as one of the first diagnostics.