First time on.... I have 2 of my family'* Bonneville'* down.2000 and 2002 SE They both have stalled while at 55mph. they would start but not run more than a second. Start and die 20-30 times. next day start up on one , the other not always.the fuel pressure is there and a new pump was installed on the other. No codes except IAC motor stuck on one which is probably unrelated. The start/stall seems like a security fault which wont let the fuel rail do its thing,but the security system wont stall the car out. They both stall sudden with no hesitation,like the key is turned off.they both start at the turn of the key. Is there something that will stall a 3800 and also activate the security system to not let the fuel rail activate. they both run fine now but cant be trusted to drive to work, or college. Tx

A security system issue will not result in the car starting then stalling.

Could be a bad fuel pump. Check fuel pressure and let us know what you find. One the one where you installed a new pump, check fuel pressure as well just to rule that out.

Could also be a bad crank shaft position sensor, which is very common on these cars. When they stall, is it like someone flipped a switch and they just shut down?

the one with iac stuck may be related because its not going to be right at idle and may stall. it can be narrowed down if you put the gas about half way down as this will be past the idle. alot of times you can just clean the cone and the seat in the throttle body

I'm with Justin. That IAC issue IS related to your stalling issue. Replace the IAC, clear the codes and retest.

Now, with the other, it still could be an IAC issue also, but not throw out a code. Inspect/Clean/Reinstall.

both stalled when warm driving at 55-65 mph both would fire up at the turn of the key but only run to a rpm ,maybe 1000 and die immediately. I have read that a different module controls the start to about 400 rpm then another mod takes over. Would a cps stall a car and prevent a fuel rail operation but let the initial startup to happen?

No, no and no. If the crankshaft position sensor were to fail, the PCM falls back onto the Camshaft sensor for timing. Neither of those 2 sensors has anything to do with the fuel rail(which isn't controlled at all) or the fuel pump.
Now, the ignition control modules on the other hand, when they start to fail, will be fine when cold, but when they get hot, they fail. After they cool off, they work again. You can use a hairdryer on them to test that theory.

Have you had both the cars scanned for any new codes yet?

Both cars have no codes. One is sitting at my house and starts and runs,the other is at my mechanics and he wants to run it in hopes it will act up. Both stalled after 30 to 60 minute driving . Hair drier ??? On the base of the coils?

yep, the base of the coils and see if it quits.

and the icm controls the spark till about 500 rpm then the pcm takes over

Oh buy the way ,I noticed a thanks count on the left. Many thanks !!!

heat gun would be better but most people dont have those. let us know how you make out