denley

i messed with it some just a min ago, checked the oil and it still had some gas in it so i changed it again and started it and the roaring noise was almost all gone, but the rough idle was still there. i started messing with vacuum hoses and i unplugged the hose from the intake manifold to the fuel pressure regulator. rough idle almost completely went away.....what would cause it to run better when unplugged versus it plugged in like it should be?

Ignition checks out, distributors fine, new distributor cap and rotor, plugs and wires are good. Besides a dead battery it seems to start and get ignition fine. The roaring I'm referring to is in the engine bay, almost like engine is running without oil but I did a fresh oil change before I ran it. That's why I was asking if the computer could be making the engine run rough and not ignite right or get proper fuel mixture and cause the engine to make this noise. Figured if computer was faulty it would throw an engine light.

my 94 pathfinder le 4x4 auto 3.0l got buried in a mud hole pretty good the other day, water leaked into the passenger side really bad due to it being sloped that way. The ECU was under water for a while and was filled with mud causing it not to start, so i bought a used ECU to try. It worked as far as getting it started but now it runs terrible. It feels as if it idles at 300 rpm and almost wants to die until given gas very slowly, after giving it gas it seems to run fine except a roaring noise from the engine. Would a faulty used ECU cause it to run very rough and make an awful noise? Is there any way to test the ECU to see if its an internal engine problem instead? Oh also there is no check engine light or and other hazard light on the dash. Any help is appreciated. Thanks!!