Midke, there are several things to try.

Regards oil pressure......
Mahle or Mann oil filter only. Nothing else.
Add Marvels Mystery Oil to the oil - this is a very fine cleaning agent.
After adding, run it a couple of hundred miles, then change oil.
Switch to 15W50 Mobile One Synthetic.
Consider replacing the oil pressure relief valve and spring with new.

I did all the above except the relief valve and spring. it virtually
eliminate the infamous :Vanagon Syndrome" for me....ie clacking valve
lifters on start up. Of course you ar eaddressing low oil pressure at
idle, and I am sure some of these things will help.

Regards popping, misfiring at idle:
Add Marvels to a full tank of  fuel. Again, a very fine cleaning agent.
This application is mainly for cleaning the injectors. Run out the whole
tank of fuel.
Replace your Temp II sensor.
Remove, clean, and re-install your grounds, especially those on the left
side of the engine.

These items don't target a specific fault, becoem synergistic. All
together they should help the situation.

Regards,

John Rodgers
88 GL Driver

Mike D. wrote:

> Thanks to all of you who responded (both on or off list) about my new
> engine/rebuild questions.   After fixing a bizarre problem (loose
> throttle body -- see other email), I'm back to square one with
> regards to my evaluation.
>
> The situation:  85 westy automatic, 150k miles, automatic, CA emissions.
>
> - When warm, low oil pressure light comes on under 1100rpm.  I'm
> running 20w50 with a good filter and it has already had the 0.3bar
> switch mod.
>
> - When cold or warm, has rough idle, with lots of little backfires
> (pop).  If  you give it the slightest bit of throttle, the idle
> smoothes out.  Mechanic thinks the lifters are not lifting due to low
> oil pressure at idle, causing the rough idle.
>
> - Runs fine on the freeway -- I can cruise at 70, get about 17mpg,
> and it passed emissions last year.
>
> - Mechanic said "quite a bit of" metal in the oil at last oil change.
>
> The question:  Do I need a new engine, and if so, how soon?
>
> Since I'm not terribly impressed with my mechanic's diagnostic skills
> at this point, are there any other things that could be causing a
> rough idle with backfires at idle?
>