papadekaitlyn

I have an '87 Toyota Pickup with an engine from a '88 Toyota Pickup in it (recently installed it; no rebuild). When I am driving, once the engine reaches operating temperature, the engine hesitates when I decelerate causing the truck to surge. Seems like when this happens there is also a slight miss. So far my guess is that it is either A) The EGR Valve, B) The Carburetor or C) A Head Gasket issue. There is no oil in the water or water in the oil. Once I decelerate, if I try to hold the accelerator slightly to maintain a speed of 50-55 mph in 5th gear the truck constantly hesitates causing it to momentarily slow then jerk forward. I have replaced the fuel filter, inspected the distributor base plate to make sure the timing advance is working correctly. When the truck is parked and I accelerate the engine everything works as it should under normal op temp. Timing advance, etc work correctly. The issue only occurs when I am driving. It does it in 4th gear as well. I believe when I am accelerating through 1st, 2nd and third I can feel a bit of a miss once I get to the top of each gear's range, but there are no serious hesitations causing the truck to jerk except in the high range gears (4th and 5th)

I have new plug wires, plugs, cap and rotor button. New Air filter, new fuel filter, new PCV valve. I adjusted the valve lash to see if that would help but it did not. I replaced all of the old vacuum lines as well. What are your thoughts on the causation of this issue.

ttoad91

my 86 does that. when i lift off the throttle in the higher gears it jerks and surges pretty bad, but it accelerates smoothly i cant figure it out. mine is fuel injected to it must not be your a fuel issue?....

bipolarandproud

My truck did that a few time when the knock sensor plug would fall off, Idk if that helps any ...

papadekaitlyn

I did figure out the issue actually... The vacuum switch that is mounted on the passenger side fender well and leads to the distributor had the wire severed. I had to reconnect the wire to pin 11 on the ECU computer and now it runs as smooth as creamy peanut butter. The EGR valve is a contributor too. I don't have any exhaust pressure on the vacuum line going from the EGR to the EGR modulator, so I know that the valve isn't functioning. That accounts for the occasional pop I get when I hit the clutch or decelerate.