Choking...loading...?

[ChadLee]

1989 240 GL with 310k miles

My wife has complained about our wagon "loading up" and I have never experienced it until this morning. I have been driving the car every day for the past 6 months trying to see what she was talking about with no signs of issues. Today it started fine and after warming up for about 5 minutes it began to chug like it was not getting fuel or air or mixture was off. Last night it was parked nose down at an angle (a first in the 6 months) and it took longer to warm up due to a cooler morning. She mentioned that this issue seems to happen when letting it sit stationary and warm up too long. After a few good revs it seemed to "clear itself" and I drove it to work without any more hang ups. I have done the flame trap/pcv, plugs/wires, vacuum hoses and MAF in the past year. Any help on some self diagnosis would be beyond amazing.

Thank you!

[jimmy57]

On 240s of that year range an exhaust leak at manifold to head or at front exhaust pipe to manifold can let air be sucked in between exhaust pulses. The signal will go lean on oxygen sensor as a result and it will richen mixture. At faster engine speeds the pressure pulses are less likely to draw in the air.

[ChadLee]

Is there a way to test or remedy this in my driveway?

[93Regina]

...exhaust leak at manifold to head or at front exhaust pipe to manifold can let air be sucked in between exhaust pulses. The signal will go lean on oxygen sensor...

At what point in time does Closed Loop happen?

[93Regina]

Is there a way to test or remedy this in my driveway?

Got ears?

[ChadLee]

If my ears hear something, what might that be and how will they remedy the situation?

[93Regina]

If my ears hear something, what might that be..

Exhaust leaks...

Btw, has the Airbox Thermostat Valve been changed, or by-passed?