Q: My car turns off when driving or if left running it will turn off while idle.

My car will turn off while driving or if I leave it on idle it'll run for a little bit then turn off after awhile. Sometimes when it turns off and I try to turn it back on, it will turn over, but it wont catch and smoke will come out of my air filter. When my car turns off the dash will still be lit up as if I was about to start the car again so I don't think its any electrical problems, plus I've already had electrical work done to the car already. I was told by one mechanic that my throttle body could be clogged up because one of my PCV valves tubes was cut open and was clogged up with black thick stuff and that tube led right to the throttle body. I already know it's not my fuel filter or alternator because I changed out my fuel filter and I tested my alternator.

My car has 250000 miles.
My car has a manual transmission.