1997 pontiac bonneville 3.8 engine car usually runs fine then on occasion the tachometer needle will bounce a couple times, the car will buck a little then stall, sometimes starts right back up and sometimes you have to let it sit for 10 or 20 minutes sometimes a hour or so, then it will start right up like nothing was ever wrong. ????

SOURCE: 1996 Camry 100 km stalling

You have one of two very common problems.
Number one may be a stuck open EGR valve
Number two would be a failing Idle Air Control valve (IAC).
Try this: Open the hood & locate the EGR valve, close to the firewall, behind the intake. Find & take with you a small hammer. The next time that it happens, open the hood & tap on the EGR valve. If it is sticking "open" the tapping may dislodge the carbon particles that are keeping it open.When the EGR valve is open, exhaust is getting into the intake at idle, and this will def stall out the car.
There is no repair to the IAC valve, it would need to be replaced if it is bad.
One of these two scenarios will cure your problem, I see it every day.

SOURCE: Car starts then stalls once the engine warms up.

You need new timing belt and gears. Buicks gears are made of plastic, and become a big glob. Nothing for the timing belt to grab onto.

Marvin

• 85242 Answers
• Posted on Oct 28, 2008

SOURCE: 2000 323i stalling when i slow down

Here is what you need to do, a cleaning of the intake throttle blade and the idle speed control air-bypass valve, they get full of gunk over the miles and cause idle issues (stalls) like yours,
Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the engine at idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake

SOURCE: 1995 pontiac bonneville stalls

I just went through lots of troubleshooting and expense on my 1996. Whenever I would lift my foot off the accelerator and was below about 30 mph, the rpm's would starts jumping around and sometimes it would stall. If I gave it a little gas (accelerator), I could sometimes keep it running. It also backfired once in a while. Starts right back up. Also, if I let it idle while in part, it would die after 1-2 minutes.

I ended up finding a hole in the fuel regulator. About a ~$70 part if you get an AC Delco, but very simple to change.

SOURCE: 1997 Bonneville 157K, driving and just stalls

sorry to say this, but sounds like the engine might be done, starting to seize up, have someone do an oil sample to see if any metal in the oil