When I start My 1998 buick regal ls 3.8 it idles rough and stalls most of the time, the rpm's go up and down as soon as I let go of the key. If I step on gas for a few seconds it stays running. Motor

SOURCE: engine stalls

your on the right route but also check egr valve

SOURCE: buick lesabre nightmare

Need to get a scan tool and look at the data stream while it is running for alot more info.Also any trouble codes.Sounds like initially,the engine isn't getting any fuel.I would have a pressure gauge connected to the fuel rail on the engine,so i could monitor the fuel pressure while all this is going on.Items to look at on the data stream would be timing,what timing is the PCM commanding for the engine.Also,have you checked for continuos power feed to the coils during this no start condition,and fire at the plugs while cranking.You could possibly still have spark,but maybe it is extremely weak?I have seen bad ignition switches cause weird problems before too.Many things power up through the ignition switch,just a thought.Have also seen bad PCM's cause strange problems..38 volts is a little on the low side for GM.Usually see those at,at least .50 and up,and rise steadily while pressing the throttle,up to just under 5.0 volts.Potentiometer with 5 volt supply.Vacuum leak can be checked with engine running at a steady idle speed,spray brake cleaner all around the intake manifold and listen for engine speed change.

SOURCE: buick lesabre no start

Hi you have replaced allmost everything ,(try fuel pump relay)

SOURCE: 1999 Buick Regal GSX won't stay running......

It's probably the mass airflow sensor and/or oxygen sensors.

SOURCE: hello i have a 1995

Try plug wires, that's about all you haven't replaced. Actually if you have an ohm meter you can test them - anything over 6k ohms per foot - REPLACE them. Also run a good fuel system cleaner through it and stay away from cheap gas.