Q: Car Trouble

when I come to a complete stop & then press the gas, my car jerks( like it's being kicked) Also, it starts to jump on & off if I stay on the gas too long. My "check service engine" light never comes on though.

I recently took a trip & drove it for 3hrs. It wouldn't go over 70mph, then my "check engine light" flashed on & off (for the first time). I've took it to plenty of places to be looked at but nothing ever shows up when they hook it up to the monitor. So, they can't find out the issue. Any suggestions, on what it could be?????

Thank you!

My car has 167000 miles.
My car's transmission is unknown to me.