i just got a 94 pickup 3.0 5 speed last month. i have noticed at about 1/4 throttle which is about 1800-2300 rpm in any gear the truck bucks and jerks like the clutch grabs then lets go, then grabs and lets go again until the rpms get over 2300 or so. the truck will start bucking and jerking and when you go past 1/4 throttle or let off to less than 1/4 trhottle it will quit. I also noticed it doesnt hapen until the truck has warmed up a little like 10 minutes or so of driving.

what has been done to this truck:
-new spark plugs
-new distributor cap
-new rotor cap
-new plug wires
-i have unplugged o2 sensor and nothing changed
-i have tested the tps off the truck and found nothing wrong (i used a Snapon multimeter to check and i know how to use it) and i think i re-adjusted the tps right (according to the 4wheel crawler page i think).
-new fuel filter

i am thinking either the tps isnt right, the ecu is messed up, the clutch is maybe glazed over (i reall doubt this one tho since it doesnt slip at all), the fuel pump, or maybe a valve issue. The assenger side has a faint tick like maybe excessive valve lash?? Ive been told that maybe a valve could be floating but not sure since i thought thatd hapen more at high rpm?

Any ideas???

Thanks Travis

 

no ideas???

i have also already tested the igniter and the ignition control module, too.

 

Disconnect the vacuum line betweenn the EGR valve and EGR modulator. if the problem goes away there is something wrong with your modulator system. Normally I'd say to verify your VAFM doesn't have a dead spot but if it's only happening once warmed up that's not likely the problem.

 

i unplugged the vacuum line thats on the egr valve that points towards the front of the truck and it stoped bucking.

where do i start testing to figure out what modulator or valve is causing the problem?

 

There is a procedure in the FSM for testing the modulator. Something about plugging certain holes and blowing into other ones. When I got my truck it wasn't bucking, but it was constantly throwing a code that the EGR temp. sensor was malfunctioning. It turned out to be that one of the hard vacuum lines between the EGR valve and the EGR modulator was plugged. So, check there first.

Autozone had an EGR modulator is stock. I think it was $50. If that is your problem, it's a really easy fix (takes about 37 seconds to swap out).

Also, how in the name of all that is holy did you know that it was the EGR modulator, CO_94_PU?