94 rough idle and knocking when accelerating

I have a 94 350 and it idles rough. It sounds alright but if you are sitting inside the truck you can feel it vibrate and shake. It runs fine, accelerates smoothly, no stalling etc. But at certain RPM's when you are accelerating the engine knocks. Especially when you hit over drive and have your foot on the gas. I can hear the knock sitting in the driveway if I punch the gas also. I have replaced the dist. cap ,rotor, coil, plug wires and have not noticed any changes for better or worse.

Sounds like carbon. I'd look to see if the throttle body needs cleaned.
Then I'd run some Techron through it, find an open stretch of road (even better if steeply uphill) and run it wide open up through 4000 RPM. Slow it back down and open it up again. I'd do this 4 or 5 times. The Techron and hard running will clean it out.

The two top reasons for knock (I assume you mean spark knock, or pinging, or knocking, or detonation, or preignition, sounds like small gravel shaken in a tin can) are lack of EGR flow and carbon in the combustion chamber and on the intake valvestems. Give this a shot.

Also check the EGR by pulling a vacuum on the little flying saucer shaped EGR valve when at idle. It should almost stall the engine. If not, you have plugged EGR.

Other causes include lean mixture (warmed up at cruise it ignores the MAF and uses the O2 sensors which are very reliable), hot engine (use factory thermostat), fuel pump or filter (would be much worse at high RPM and wide open, not what you described), advanced ignition timing (not adjustable). Good luck.

My 94 1500 5.7 does something similar. Runs fine at high speed but when you come to a stop rpms drop to about 200. At idle rpms are around 500. Would this be the egr also. I changed fuel filter, plugs look great. I have run ejector cleaner through it now. Thanks for any more help. :banghead: