Intermittent misfiring or sputtering.Have to floor it to get it to run correctly on 2001 Dodge Dakota

replaced every engine sensor for evap sys.good fuel pressure.new distributor,new wires,pulstar plugs.this problem is all over internet but no fix.thought i was good mechanic but banging my head on this one.pops code for multiple cyl misfires and that's it.seems to do it more when hot but not exclusively.i have a throttle body spacer and performance chip on IAT sensor.The shop said computer was good and they can't find it couldn't fix it.Could it be intake plenum leak?I'm tired of hearing it's a dodge thing!

by in O'Fallon, MO on August 20, 2011
1 answer 1 comment
ANSWER by on August 21, 2011
Really need to get into the scan data, a misfire for all the cylinders, i.e P0300, can be caused by many, many things. If you see scan data, look at the long term fuel trim, is it lean or rich compensated? ( lean = higher percent like 12-15%, rich is negative same type of numbers. ) Do a manifold vacuum test when the truck is idling, if the vacuum gauge jumps around at idle, you may have a mechanical issue. If it is smooth, it is most likely an air-fuel/ignition/sensor issue. A scan tool with the data output is essential to deal with these types of problems, codes only tell you something is wrong in a really general way.
COMMENT by on August 22, 2011
Thañk you so much for the guidance.Your troubleshooting logic makes sense to me and I will follow yôur advice.If it turns out to have a "shaky"vacuum at idle what type of mechanical issue would cause it?Could the plenum gasket leaking cause this problem?Could it simply need a valve job?I have replaced pretty much all the sensors under the hood including the TPS,IAC,Water temp,IAT, cam,crank& distributor.I even replaced all the O2's and the ambient air temp sensor.Could a clogged catalytic cause it?If it is a air/fuel ignition sensor issue what else is left?The computer?Your input is valuable and appreciated.