I have recently installed a remanufactured crate engine, but the problem I have was in both engines. The engine seems to be missing at other than idle RPM ranges. It idles smooth, but having it in park or neutral and accelerating to above 1000 RPM it runs smooth for a few seconds and then the RPM starts fluctuating approximately 100-300 RPM. I have scanned for codes and have no codes. I have spent a entire day with a mechanic and he checked ignition and fuel delivery with no problem shown. He also checked for vacuum leaks and found none. he did a cylinder balance test and found no problem. Checked voltages and repalced a defective throttle position sensor that had a spotty carbon disc. He determined is that the EGR valve is opening too soon causing the miss. When the EGR EVR solenoid electical connection is disconnected is improves the miss, but it is not entirely corrected. The EGR valve and position sensor have been replaced. I have tried a different EVR solenoid. The OS sensor, intake air temperature sensor, have been repalced. I have tried a different ECM from my other 1993 F-150 with tht same engine and transmission,but not a 4X4 with no results. I have replaced the fuel injectors with professionally cleaned and tested, with new o rings and pental caps, used injectors. I've had the transmission checked. I've replaced the fuel regulator and tested the fuel pressure and it's within the recommended ranges 35-40 key on and 30-35 engine running. I've

swapped the MAP sensor and ignition module from my other 93 with no results. I have replaced the fuel pump in the front tank due to an inoperative fuel sending unit. I'm at lost on what to check next. I'm at the point of taking it to a Ford dealership, but I don't have good feelings as to them finding the problem but to start replacing parts that have already been replaced. and charge me an arm and leg. At this time I would almost be willing to give up one of them.