Sentra rough running when cold, idle drops when warm

[Jim McClure]

I wrote about this once before.  I've checked a few more things and the symptoms are getting worse.

The car starts easily and runs smoothly for the first 10 seconds.
Then it gets progressively rougher so that it won't run below 2000 rpm.
I have to hold my foot down on the pedal to get it to run.
After it gets to operating temp, about 5 to 10 minutes, it smooths out.
Sometimes, about once and hour, if I'm driving around town, the idle drops to 500 rpm and then the engine
goes dead.
If I catch it and pat the accelerator, it will smooth out at 800 rpm and not go dead.
It is not cold here.  Normally 60 degrees in the morning.

I checked a few things and did some general maintenance.
The valve cover gasket was leaking into the spark plug holes.  The plugs were under a layer of oil.
So I fixed the gasket and replaced the plugs and wires.
I checked the compression and it is 175 in all four cylinders.
I also replaced the distributor cover and rotor.
I cleaned the throttle body.  Set the ignition advance.
Adjusted the idle air screw.
Replaced the fuel filter.

It is getting 28  mpg, so the overall performance is good.

By the way, in the middle of this problem, the Hitachi starter went out. I bought the last one from
O'Reilly auto parts three years ago and it had a forever warranty.  They had my name in the computer and
gave me a new one, no questions asked.

I'm working my way through the idle procedure, but thought you guys might know the answer.

Also, you normally access the idle air control from under the car?
The procedure says "check the idle air control valve" but how do you check it?  Take it off, put power on
it and see if it opens?

Thanks,

Jim
'93 Sentra SE-R