I have 1993 Nissan Pickup that was recently ran through a mud hole that
splashed up under the hood covering everything with mud. The truck ran very
rough. I looked under the hood to find water in the distributor cap and mud
in the throttle body. I replaced the cap, rotor, plugs and wires. I also
removed the throttle body and cleaned out all the mud. It would then idle
but missed at the lower rpm and would miss at high rpm when driving.

I thought it seemed like a vacuum advance problem. Since the truck is fuel
injected and has no vacuum advance I decided to investigate the workings
down inside the distributor. I pulled it out being careful to mark
everything so I could put it back in exactly the way it came out. Everything
was clean inside the distributor so I put it back in the engine. It would
not go back in like it came out. I assume the rod going to the oil pump came
out partially when I pulled the distributor and fell back in turning as it
did. I had to rotate all the plug wires one hole to get the engine to start
and run. I have tried advancing the and retarding the timing but it has
little effect on the low and high rpm problem. I don't know for sure where
to set the timing and don't see and marks to use a timing light on.

A mechanic told me to check every vacuum line to make sure they were not
full of mud. I have and they were all ok.

I don't know what to do next. The mass air flow sensor looks fine. If I
disconnect it the rpms change. The sensor in the air cleaner looks fine and
disconnecting it effects the rpm. There are 2 sensors on the throttle body
opposite the mass air flow sensor. One has a small plunger and spring. When
I disconnect it the rpms are not affected. I believe it has control of the
idle air flow. The sensor below it had a lot of carbon in it and has some
kind of a double spring and plunger. I don't know its function. The throttle
position sensor ohms out nice and smooth 0 -10 ohms and is set at 2 ohms in
the idle position.

Anybody have any ideas on how to test or check to see what the problem is?
How to set the timing and where it should be set? Thank you.