1990 Reatta Stalling when rpm's drop below 1200

[retiredarnold1]

My engine is stalling after dropping below 1200 rpm's.  Car has been in storage for 5 yrs, tho I have started and ran the engine during the years.  The car started right up after charging the battery.  Went to the local oil change for a change of oil and filled the gas tank.  Parked in the garage.  2 hours later went to start car and it just turned over and did not fire.  Pulled a spark plug wire, turned the car over, no spark.  Got on line with Reatta Owners Journal and began the troubleshooting process.  The ICM was a gluey substance and the coil had a broken connector.  Replaced them with new parts.  Turned car over, no spark.  Put in new crankshaft sensor, cam magnet, and cam sensor.  Car fired right up, ran for about 2 minutes then stalled after dropping below 1200 rpm's.  Proceeded to clean the IAC sensor and hole, MAF sensor, EGR valve and did the seafoam process as specified in the ROJ (twice).  Car fired right up, stalled after rpm's dropped.  Put in a brand new ECM, engine started then stalled.  Replaced the MAF sensor and IAC sensor (made sure it was not longer then 1 1/8 inch long).  The engine ran worse with the new so I put the old sensors back in, the engine ran better but still died after rpm drop.  The codes I have are E448h, E034h, and E042h. Most times the service engine light is not on. Today I fired the cold engine up and as it started to warm up it would drop close to 800 and 1000 rpms but the engine would speed up the rpms and didn't stall until it was warmer after two minutes.  The rpm's dropped, the engine shuddered than stalled.  I cleared the codes and started the engine (it struggled to fire up but it did) and feathered the gas so the rpm's wouldn't drop.  I rechecked the codes and the code was E042c.  I have driven the car using the shifting into neutral and keeping the rpm's up above 1200 to the golf course which is 3 miles away.  It runs fine until the rpm's drop and stalls.  I have no idea what it is causing the engine to stall.  Haven't check vacuum hoses for leaks, changed the plugs or wires, or the fuel system diagnostic. Could the new coil or icm be bad or another sensor I replaced?  I'm thinking Buick service center at a dealership might be my next step.  Anybody got any suggestions?

[2seater]

It sounds like a possible vacuum leak. When cold the rpm's are raised and the mixture is richer which may mask the excess, unmetered air. A commonly overlooked vacuum leak possibility is the PCV system buried under wires at the passengers rear of the intake plenum. You have already hit many of the common culprits.