My engine stalls at idle?

Hello,

Two things come to mind, the first is it could have a vacuum leak, here is a guide to help you confirm the problem.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

If this seems okay the other would be that the throttle bore and IAC if it has one needs to be cleaned.

Here is the guide for that as well.

https://www.2carpros.com/articles/throttle-actuator-service

Please let us know what happens.

Cheers, Ken

Lets try the idle air control valve

Disconnect the air intake ductwork from the throttle body.

Start the engine, then increase and hold the idle speed to 1,000 to 1,500 rpm.

Spray the throttle cleaner or engine cleaner into the throat of the throttle body, aiming for the idle air bypass port (usually located on the side or top of the throttle body opening). Give this area a good dose of cleaner (about 10 second's worth).

Turn the engine off to allow the cleaner to soak into the IAC passageway.

Wait about three minutes.

Restart the engine, rev and hold at 1,000 to 1,500 rpm, and repeat the cleaning process again.

Turn the engine off again, and reattach the air intake ductwork to the throttle body.

Start the engine and rev and hold to 1,500 to 2,000 rpm until no white smoke is coming out of the exhaust pipe.

If this fails to make any difference, you can remove the IAC valve from the throttle body and spray cleaner directly on the tip of the valve and/or into the ports in the throttle body. Let the cleaner soak awhile, repeat as needed, then reinstall the IAC valve, start the engine and run it at 1,500 to 2,000 rpm as before until no white smoke is seen in the exahust.

If the idle speed still surges after this, the IAC valve is defective and needs to be replaced.

A code P0141 may mean that one or more of the following has happened:

open or short to ground in the wiring harness
O2 heater circuit wiring high resistance
O2 heater element resistance is high
Internal short or open in the heater element

Possible Solutions Replace oxygen sensor (cannot repair open or short that occurs internally to sensor)
Repair short or open or high resistance in wiring harness or harness connectors

Check and test the wires and connection

You may have a vacuum leak from the brake booster, to check, remove and block booster vacuum hose at the booster, start and apply brakes, if engine does not falter, you will have a booster problem, do not drive with booster disconnected and brake will be very heavy and stopping power will be poor.

You may have a bad catalytic converter, especially if you never replaced it.
Check for backpressure.
You can also check the difference in temperature between the converter inlet and outlet.

"P0140 I noticed it said intermittent and the P0141 was pending. I'm really going WTF? I know it's hard to detect the problem directly, but what should I do next? Is the O2 sensor atfer the cat bad or can the cat be bad?"

What o2 sensor are you replacing. Both these codes are related to the rear o2 sensor "post cat converter".

Replace the o2 sensor after the cat converter