Still battling with my 98 Lesabre.
I can drive the car to work, but if I start it up after sitting for 20 minutes or so, it wants to stall when I put it into gear (reverse or forward). I only have the stalling problem after the car is warmed up. I have replaced the PCV valve, the spark plugs and wires, the battery, the mass air flow sensor, the upstream O2 sensor, the alternator, the purge valve/solenoid, the idle air control valve and the fuel pressure regulator. I have also cleaned out the throttle body. I took it to the local mechanic and they found I had a vacuum leak and fixed that. The mechanic also said the upstream O2 sensor I installed wasn't working properly so I had them replace that as well. After all this I am still having the stalling problem when the car is warm and I put it into gear. Could there be a problem with the crankshaft position sensor? I do not have a check engine light on at this time.

Have you replaced the CTS, coolant temperature sensor? I did not see this on the list of parts that have been replaced. The CTS supplies info to the computer as to how much fuel to supply when the engine is cold, mid range and fully warmed up. Actually at all points of engine temperatures. There are obviously other inputs besides this but the CTS is a suspect in my opinion. I hate to throw parts in order to solve issues but at least the cost is reasonable and it is super easy to replace at least on my 2001 Park Avenue. The CTS can be tested with an ohmmeter and I think that google would reveal the test procedure if this seems appealing.

Beyond this, I think some scan tool data would be helpful. For example the scan tool data would give your engine RPM at idle in Park, when cold and when fully warmed up. My 2001 Park Avenue has basically the same engine as yours. My RPM is 650 in drive when fully warmed up. This is the situation that you have when your stalling takes place. If we knew your engine RPM this may help.

Did you figure out the P1134 code from the other thread on this issue?: https://www.gmforum.com/buick-172/98...o-gear-312491/

I believe it was a sluggish upstream O2 sensor

I will try and grab my scan tool later and get back with some data. I appreciate the input!

Meant to say I believe the P1134 code was from a sluggish O2 sensor.

So what fixed the sluggish oxygen sensor?

Not 100% sure honestly, just swapped out the sensor for a new one.

That would fix it.