88 Buick VIN 3 stalling, ECM?

[Lynn R. Erickson]

Some background:

88 Buick Century wagon with 3.8 SFI(hah) V6, approx. 97k miles

My parents bought it new in 88. They decided to get rid of it about 5
years ago because it had always idled rough, left them stranded once
(crank sensor), and was intermittently prone to stalling when you let
off the throttle at low speed around town. Figuring that an intermittent
will eventually get bad enough to be continuous so that it could be
diagnosed, I bought the car from them for my wife. My wife likes the
car, and the rough idle and infrequent stall didn't bother me. _I_
wasn't driving it.

However -- last week I drove it to Los Angeles and back(800+ miles each
way). You haven't lived until you've had a car stall in the middle lane
of Century Blvd. at LAX. I decided to fix the damn thing.

Some symptoms:

_seems_ to be heat related
No problems at freeway speeds
No ECM trouble codes
During the sensitive time in LA, parking lot speed bumps would cause
static on the AM radio and make the CE light flicker on.
Still idles like sh*t -- never hasn't. Not just 90 degree V6 rough,it
also misses.

Diagnostics:

All cylinders 140-150 psi compression cold. Hot? You jest! Not on my
skin!
New plugs and wires. Needed anyway. No change.
New PCV. Needed anyway. No Change.
10" hg manifold pressure at idle. Is this normal? Reading taken from
transmission vacuum line.


Got a scanner hooked up today. Following readings are at idle.

ECM PROM ID 1254 -- The ALLDATA CD shows a stall related TSB on this,
but it isn't included in their (extra cost) TSB's. Sigh. ALLDATA is
better than Chilton's, but watch out, some of their information is
missing or flat out wrong (I got bit on a wiring diagram).

Some readings:
                  ALDL Mode     Diag. Mode    Backup Mode*
RPM               1000-1100        650          675
Coolant Temp.     196 F            206 F        217 F
Intake Air Temp.  156 F (why?)     86 F         84 F
TPS                0.4 V           0.4 V        0.4 V
O2 sensor         400-600 Mv       473-549 Mv   920 Mv*
Spark Advance      28.6 deg        0 Deg        0 Deg
IAC Position       51              38           49
Integrator         132             129          128
Block Mult.        133             133          113
EGR Duty Cycle     0 %             89%          79%
EGR Switch         Off             Off          Off
Closed Loop        On              On           Off
Fuel Mix           Lean/Rich       Lean/Rich    Rich*
Learn              On              On           Off

*Sets O2 sensor rich error code.

About all I can figure out right now is to try a new ECM and get the
latest service release on the PROM. 

Anybody got any other ideas?

TIA,

Lynn

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I may be stupid, but I ain't _that_ dumb.
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