Why does it feel as though it's going to die as I am at idle in park and/or while in gear sometimes?

fuel filter,coils module.

Disable the EGR valve and test. If issue is resolved you have 3 plugged EGR ports and all the EGR flow is being routed to # 4 cylinder resulting in misfire or the EGR valve is sticking open at times though you probably would not feel a misfire except @ idle & take-off.

I think I would check the fuel pressure and the maximum fuel pressure from the pump.
I would look to data if temp sensor , map, tps,
lack of power can be cause by many things
hope it helps

Sometimes that's caused by a vacuum leak near the manifold area.

Sometimes air in the coolant will cause an idle problem. Air will keep the air temp sensor from sending proper info.
Hope this helps.

try having the fault codes read first then fixing the faulty sensor
indicates a fuel pressure or injector problem

check fuel pump.if there is a small , even hairline crack in the diaphram it will do as yours does. good luck.

dirty throttle body, check air filter.

Hello,
The problem you are experiencing with your car is as a result of a bad fuel pump or a clogged fuel filter,the fuel pump supplies fuel to the engine,but there is an epileptic power failure in the fuel pump when the car accelerates at times,hence there is no sufficient fuel supply during acceleration therefore the car engine dies at times when accelerating.
The solution is to replace the fuel pump/clean out or replace the fuel filter of your buick.


Have a nice day!!

It sounds fuel related the fact that it idles rough and you lack power causes you to press the accelerator pedal more to to get the car to go which in turn causes the transmission to stay in 1st and 2nd gear longer bringing up the rpm's. The problem could be a bad fuel pump not allowing proper fuel pressure to reach the injectors This could also be caused by a bad fuel pressure regulator valve or a bad fuel filter all of these could cause low fuel pressure. It could also be a bad fuel injector or a throttle position sensor (TPS) could also be a bad (PCV) I would suggest having the fuel pressure tested first as I dont think your problem is related to the transmission repair you had done.

hey-I have has this before different car but same - idle control valve is failing - computer at shop will pick this up on diagnostic