Idles fine in park for about 40mins the dies. Restarts runs for 2-3 minutes dies again.
I changed fuel filter which definitely needed.
Then proceeded to let it idle in park as before. Still dies after 45-50 minutes. Which to me means something is getting warm/hot and cutting out. The motor does start right up.

I then drove it down my private road. The rpm drops even at steady 20mph, then rpm regains.
Took it on main road up to 70mph drove a few miles, it fluttered a couple times bringing check engine light on but then regained itself and check engine light went out. I went back on my private road and it died while maintaining speed. Started back up and got her home. No codes stored.

I should mention before this, I drove it back and forth from work which is a hour drive with no issues. 3 fuel fill ups and each time my mileage went down 2mpg. From 21mpg to 17mpg.
I decided to take it on a long trip but wanted to make sure it would make the long drive, so I idled it in my driveway and then all this started.
Tried to upload short video but mp4 isn't allowed and that's what my video is done it.

 

Fuel pump could be dying?

Any CEL codes?

Oxygen sensors are dying?

Could also be as simple as replacing the Coolant Temp Sensor.

Coils could be dying too, as when they get hot, they might start arcing out?

There are a lot of options.

You could have a vaccum leak.

Assuming that the car stalls while at idle only, I'd rule the TPS and MAF sensor out. It'd be nice to confirm whether the car goes into open loop. You'd need an OBD2 reader to do that. Do you have one?

 

My immediate response is go after the oxygen sensors.
The oxy sensors trim the amount of fuel going into the engine via the engine control module (ECM).
If the sensors are faulty, then the ECM will leave the engine in a full rich mode which would explain your poor fuel consumption.
As it appears you are in North America then the downstream sensors will be the problem.

 

Ok here's what's been done before this issue. I had tolerable warm air for heat and gauge sat at C, unless it was a warm day then it would slightly sit above C.
I assumed previous owner removed the thermostat. I opened the housing and found thermostat was there but a brace on it broke leaving it in the open position. I replaced thermostat and gauge and heat work as it should.
Filled up gas calculated mileage, drove to work drove home. NO issues.
Now after my above post, I cleaned throttle body and noticed previous owner didn't bother to connect the oil sensor up. I did that fixed the oil gauge.
See picture of the idle control valve that I found not secured.
Cleaned throttle body and replaced control valve. Used starter fluid for vacuum leaks.
Same issue except idles at 1200rpm and 900 in drive. I expected that from what I read here, ill need a tps reset.

​​​​​​Started and idled for 10mins, drove down the road, ran great. Went home and idled it in park total drive/park time 50mins and same issue. Started it put it in drive and waited 2mins and it died.

VEE
yes on obd but not well versed in use other than reading codes and erase. See pic of type.

Coolant sensor possible because before I thought the gauge was bad and got the sensor off a junkyard donor. Ill put the old one back in and see.

O2, maybe, the exhaust from previous owner was completely hacked with half of the drivers side not even there.
I replaced to straight pipe from o2 sensors to jags chromed sound arrestors continued to jags factory mufflers. That was 500miles ago and never a check engine light, which I was expecting honestly.
Coils possible, I have replaced all 6 but aftermarket isnt always great. Those where done 3-4weeks ago. But theres no time limit on when those go. I can't see one going without a rough idle. Ive been known to be wrong.
Fuel pump possibly but should I have issues after a warm up? Should cold or hot matter?
It's not out of the question, the filter needed replaced. Could BARELY blow through it.


BILL MAC
O2S possible and does explain the gradual decline in mpg. But a smooth idle to a complete shut down? Shouldn't I get some kind of rough idle?
I'm sure they need replaced and cringe at replacement because undoubtedly they are original, the previous owner definitely had no respect on the care of this car.

Really wish I could upload these videos of it, it's like someone just reached over and turns the car off.

I do need to learn my obd2 better