i have a 1989 f-150 4.9 I6 4x4 i have replaced the iac, tps, spark plugs/wires cap and rotor, 02 sensor, and cleaned the throttle body to try an fix this but between idle and 2000 rpms when i give it 3/4 throttle to floring it it will pop and surge it will do this in nuteral and in every gear while moving but once it gets above 2000 (2300-2400 in the higher gears). i checked all the codes and the only thing that popd up is the clutch position sensor which should be irrelevent in this case i realy need help on this tryed everything my truck is always taken care of maintenace wise so its not due to neglect and the truck does not have a valve tap.... thanks Also it has a new fuel filter and oil just changed 200 miles ago clutch pressure plate through out bearing and slave cylnder changed 300 miles ago but that also shouldnt be a factor seing as it still does this even at idle

 

Check the fuel pressure, and check for vacuum leaks. Also check the MAP.

 

he doesnt have map

 

have you tied to see if your intake gasket is blown

 

no blown head gasket but im thinking its probably something in the ignition system.

 

is there a way to test the ignition module? or ignition coil?

 

take it to autozone and i didnt say head gasket i said intake gasket

 

oh my bad i will check it tomorow

 

now that u mention it i have a friend who just bought the truck just like yours only 351. it does the same thing. except for surging. it pops real bad on the bottom end. and it has no power at all. it has 35s. it can spin them in the rain. but if he floors it going down the highway its like its at a stand still it doesnt gain any speed. just stays at the same rpm. ill have to figure his out too. i keep in touch just let me know if you find anything out.

 

how does he not have a MAP?