When the car doesn't start, is there fuel pressure?  Yes, I know you hear
the pump prime, but if you check the pressure at the rail, is it good?

How did they check it?  It could be intermittent.  Clearly whatever is
bad is intermittent, and the position sensor is the first thing I'd have
swapped.

The OTHER reason you could get that error code is if you have some other
position sensor (sometimes an RPM sensor, etc.) which is disgreeing with
the crankshaft sensor.

I have no graphics here, but given the basic behaviour, I'd have swapped
the position sensor out.  If it turns out not to be the problem, well,
now you have a spare in the garage.
--scott

B1S2 fuel trim reads 99%

that is way out of bounds for a normal engine.

Correction to #2, the temp is 170, not 160.

Thanks,

Sam

OK, the first thing I thought before getting halfway through your post
was intermittant crank position sensor (CKP) failure.

You have spent a fair amount of $ already on parts that haven't fixed
the problem.  The CKP is the most likely component to cause this on
your engine, followed by the ICM (replaced), followed by compromised
wiring or shielding of the CKP circuit, and finally the PCM.  For the
cost of a CKP sensor I would not hesitate with replacing it.  I think
they are around $30 to $60.

I can't physically inspect your car to look at the wiring or test the
circuits to verify this diagnosis but I speak from experience.  It's
too bad you had several mechanics supposedly test (good) your sensor
and then condemn a $300+ ICM! + 3 coils!

It is difficult and time consuming to test an intermittant stall like
this, but with the code P0335 you know right where to start.  I would
hook a 2channel scope up to the ICM connector as follows: channel 1 to
the yellow CKP to ICM 18X reference wire; channel 2 to the blue/black
ICM to PCM CKP 18X reference wire.  You should see square waves on both
wires.  They should be sharp and defined.  Nonsensical stray voltages
would be a sign of poor shielding.  The wrong number or inconsistently
shaped waves would be a sign of CKP sensor breakdown on the yellow
wire; ICM failure on the blue/black wire.  If both signals are perfect
when the vehicle dies and sets a P0336 concurrently you should suspect
the PCM.

The sensor sits beside/behind the crankshaft pulley on the front of the
engine.  Other than loosening and tightening the crank pulley bolt,
it's a fairly easy replacement.  It would take a tech about 15 minutes
of mechanical work to do.

NOTE: You are supposed to do a "CKP sensor variation learn" procedure
following replacement.  This is a simple scantool operation that
requires a Tech II (GM mega$$ scanner), or a SnapOn with newer
software.  If I were you I just would replace the sensor, clear the
codes, then drive it and monitor the MIL.  If you never get a P1336
(variation relearn procedure not performed) then the new sensor is
lined up close enough to be a nonfactor.

If you want to explore this relearn dealio, I would suggest you contact
Jay Horak of Auto Enginuity.  He designed your scan software and
constantly responds to tech questions via email.  Ask him if the GM
software addon (about $150) has the capability to perform the CPK
sensor variation learn function on a 1997 Riviera 3.8SC.  He's very
good about product support.  I guarantee that you will be happy with
the functions and data you will be able to retrieve with his GM
software.  His enhanced software packages can be glitchy but the
reports from the field are that they get markably better and more
powerful with each upgrade.  One year of quarterly upgrades comes with
the enhanced software package.  An additional year of updates is $50
last time I checked.  I figured since you already purchased the $250+
OBDII package it would be a no-brainer to buy the 'good stuff' : )

Toyota MDT in MO

When I wrote:
It is difficult and time consuming to test an intermittant stall like
this, but with the code P0335 you know right where to start.

I meant P0336
D'oh!

Toyota MDT in MO

Whats odd is that when the car doesnt start when it's cold down a bit
it consistantly does it at 170 degrees.

Regardless of anything else, who else thinks that IAT temp looks high
for closed throttle idle?..When I see that I start thinking the EGR is
hung open.

The crank pickup is one of those 'fast start' systems that GM used?..
6x and 18x triggers?.. If I'm remembering correctly, I remember reading
that failure of part of that system would cause a no-start, but
wouldn't cause a stall.. but, admittedly, this is stuff from *years*
ago for me.

I don't know what to think about techs anymore (and this is from
someone who was one for >10 years).. talked to one tech that couldn't
troubleshoot a basic Ford DPFE system, and when he asked me about a
high idle problem on an 88 5.0 FI and told me everything he's done so
far, and I asked what the KOEO and KOER tests showed, responded that he
hadn't done those tests.

But, I've also seen someone else crimp a brake hose with a pair of
vise grips and break the hose.. dealer part; will be in Monday.

There are some good techs out there.. and, like with so many other
occupations, there are some real losers out there.

Jim