my uncle has a 91 f-150 4x2 supercab, with a 302 and auto tranny(92845 miles on it). problem is it idles a little rough(not bad) and from about 35mph and up and around 1500rpm's the truck vibrates(shakes) as if it dropped a couple of cylinders. its even worse going up hill. this is under normal driving conditions. mash the pedal to the floor and its fine. we unplugged the evr and test drove it again, problem goes away. plug in the evr and the problem is there again. checked vacuum at evr and it is good, checked vacuum at egr with truck in drive(holding brake) and brought the rpm's up to simulate a load and vacuum is good there too. (checked with vacuum gauge, vacuum matches the specs in the manual) connected vacuum pump to egr and found the egr valve would open a little and stick. removed egr valve cleaned it and freed it up and tested it again, valve is now working fine. but the problem is still there. fuel pressure is fine, tps sensor is brand new, plugs and plug wires, cap and rotor are all brand new. scanned for codes(3 digit codes on this one) and got 327 328 332 333 334, all pertain to the evr and evp which we set by unplugging them. erase the codes and they didn't come back. checked for codes again even after a long test drive and there's none. but the problem still is there. any ideas? this one has us stumped.

 

did you check secondary ignition components???/

 

When you say plug in the evr do you mean the vacuum line or the electrical connection?Does the evr hold vacuum with the switch disconnected?It could be that the evr is leaking down causing a vacuum leak.

Billy

 

thanks for the reply's, secondary ignition is definently gonna be checked next. thank you proford460. we unplugged the electrical connector to the evr, didn't notice any vacuum leak from it with it unplugged but we will definitly check it again. thank you cajunbronco