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Since i put new plugs into my 91 F250 it has been running really rough and stalls when i come to a stop. I put it on the OBD 1 reader and got codes 18 & 34. I have looked all over and even asked google what these codes meant but havent been able to find out. Also if the plugs are not firing right could that be the cause of the codes?
It would not be the first time to get a bad plug... As asked before did you verify the plugs were gapped properly? Did you replace the plug wires and/or the cap and rotor as well?
When were the codes displayed? During the Key On Engine Off (KOEO) tests, Stored Code display from Continuous Memory (CM) or when running the Key On Engine Running (KOER) tests.
The code definitions can changed based on when they were displayed. Code 18 is related to the ignition (SPOUT or IDM signal). Code 34 indicates a problem with the EGR valve position. Need to know when the codes were displayed to guide on where to go next.