Looking at your compression numbers, A leak down test is in order. My bet is Number 4 has a bad or guide preventing proper seating. Intake valves fail or get carbon build up preventing closure. If you think vacuum leaks can be bad, imagine a vacuum leak with some combination of burnt fuel mixture. Confuses the air flow meter and further messes up the mixture for the other cylinders.

Dennis

----- Original Message -----
From: Geza Polony
Date: Thursday, January 18, 2007 1:38 pm
Subject: Moral qestion--Case in point
To: vanagon@GERRY.VANAGON.COM

> Ok, sorry to belabor this one, and to the person who said it
> isn't really a
> moral question, you're right. It's a question of strategy. Going
> forward,here's a case in point.
>
> The stumbling idle on my '84 1.9 is driving me nuts. No matter
> what I've
> tried, with and without the help of the goodly folks here on the list,
> nothing has helped. New O2 sensor with good ground, tested good
> on car.
> Compression 155-155-145-130. No oil burning, no coolant leaks,
> no smoke,
> plugs all textbook-beige. New dist. cap and rotor, new fuel pressure
> regulator, new fuel filter, new idle switch tested good, rebuilt
> AFM, AAR
> removed/cleaned/tested good in freezer and warm stove (car
> starts fine.) No
> vacuum leaks--vacuum tests around 13 inches, and I've pulled the
> vacuumlines time and again to check--all of them, even the ones
> at the AAR.
> Removed, cleaned throttle body, sealed at inlet, no light shines
> throughbutterfly valve. Changed oil, used Marvel Mystery in
> hopes that would help
> lifters if they were air locked. Used Seafoam to get carbon out
> of cylinder
> heads. Changed bad thermostat. Checked all grounds and built
> ground "web" to
> all points in engine. Checked battery voltage at startup and
> running (over
> 12.5). New cat, new muffler, new rear engine mounts.
>
> This may not be the definitive list, and yes, I'm guilty of
> throwing parts
> at the problem rather than methodically testing the systems. But I'm
> reaching the limits of my mechanical ability, never so great to
> begin with,
> as well as my sanity, and so am thinking of getting my mechanic
> to deal
> with it.
>
> Therein lies the rub. He's a nice guy, easy to get along with,
> and has
> always done good work, in the sense of replacing parts when they
> obviouslyneeded replacing. But what about the (dreaded)
> diagnostic question?
>
> It's hard to tell him, OK, you have two hours to figure it out--
> then stop.
> I've done all the obvious dumb stuff already. And it could be so many
> different, unrelated things. Bad valve guides, as Dennis pointed
> out. Bad
> Hall Sensor. Bad resistence on spark plug wires. Failing coil.
> Somethingwrong in the distributor advance. Something in the
> vacuum system. Something
> in the fuel delivery or injection system. This could take days
> to figure
> out. And even then, it's an educated guess, esp. with internal engine
> components.
>
> So--instead of dealing with the problem in the past, as with the
> Boston Bob
> business, Benny, etc., how to proceed going into one of these
> situations?
> I'm almost thinking I'd rather leave it as is than deal with the
> mechanicwho can't figure it out and charges a few hundred of my
> precious dolares.
>
> Sure wish some of the people on the list lived around the corner...
>
> Sorry so long.
>
>
> Geza
>