2004 Pontiac Bonneville GXP, 70,000 miles, Northstar, runs great like new, normally starts up without problem, but about once a week it will not idle after starting. Come back in a few hours and I don’t have this problem. First time had I problem was in Dec 2021, parked car in garage for winter while out of state and came back in May, drove all summer without problem until now Nov 2022. This now happens every few days, go away for an hour and come back and it idles without problem. Brought vehicle GM dealer, former Pontiac dealer, left it there for a week and mechanic could not duplicate or fix problem. Car is too nice to get rid of, but afraid to drive.
I suggested to mechanic that it could be a faulty Throttle Position Sensor, he is more inclined to think it is a Crankshaft Position Sensor, but hesitant to proceed without being able to duplicate problem or confirm with code. The throttle position sensor seems like a far less expensive replacement if we are only guessing at this point. He wants me to return when vehicle is not performing, but it is always running super on his turf. I'm about to soon go away again for winter months and revisit issue in May. Any/all suggestions welcome.

1. No issues with starting vehicle other than maintaining an idle speed of 700 RPMs, engine intermittently stalls when coming to a stop and not pressing on accelerator.
2. Check engine light does not come on.
3. Good acceleration, no hesitation, misfires or vibrations, normally idles Smooth, no reduction in gas milage.
4. No bucking or jerking in vehicle, no idle surges, or driving speed surges.

Intermittent post-maf air leak (although you'd get a lean code here most likely) or idle air controller not working properly.

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Retired Bonneville Owner and former GM Tech:
2004 Pontiac Bonneville GXP: Black/Ebony *SOLD*

Summer Toys: Combined 827 RWHP / 877lb/ft RWTQ
2004 Pontiac GTO: Impulse Blue Metallic/Black/M6: lots 'o mods, 415 RWHP / 405lb/ft RWTQ!
2006 Cadillac STS-V: Light Platinum Metallic/Light Gray/A6 - Spectre CAI, Magnaflow exhaust, Speed Inc. tune, 412 RWHP / 472lb/ft RWTQ

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