Dodge Repair: 91 318 truck: bucks/misses on deceleration

Question
I have a 91 d250 dodge pickup with a 318 engine & 4 sp manual trans. starts and runs fine under acceleration, problem is when you let up on throttle it wants to buck & jerk !I have replaced dist cap,rotor, plugs, plug wires checked good with multimeter.also replaced electric idol control motor & ignition coil.runs very smooth until you let up on accelerator.I would appreciate any help or ideas to try . thank you, larry

Answer
Hi Larry,
That sounds like the mixture is too lean when you close the throttle. I assume you cleaned the throttle body throat and idle air passageway, and butterfly plate.  While I don't have a '91 manual I wonder whether that engine has an exhaust gas recirculation valve? If it did, there would be a small diameter pipe that branches off one of the exhaust manifolds and goes to such and egr valve. When that valve get gummed up it will fail to close tightly via internal spring-action. So look for such a pipe and then if you have it find the valve. It would have a round vacuum-operated top, a flange that separates the top from the valve body and hidden behind the flange you find the valve stem which has a circumferential slot into which you can insert the tip of a screwdriver so as to move the stem back and forth. Spray some W-D 40 on the stem where it enters the body and then move the stem back and forth to free-up the action.
The spring should close it to a dead stop.
Other than that, have you tried for fault codes using the ignition switch: "on-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. The watch the 'check engine' light, which remains "on", to see it begin to flash, pause, flash, etc. Count the number of flashes before each pause. Then repeat the process to be sure of an accurate set of flash counts. Let me know them in order of appearance and we'll go from there.
Roland