Sometimes right around 1500rpm the engine will be a popping sound, at idle same thing but most of the time it will be smooth.

Other days I will turn the engine over and it will turn itself off right after then start normal on second cranking.


The rest of the rpm range is normal except at 45mph it feels like the the torque converter or driveshaft is shaking.


This only started after using a few tanks of gas after burning all the old two year old fuel off. The problem changes how bad it is depending on the place I fill up and octane or additive.



What are the possible causes because to me it sounds like a fuel problem?

 

Could be partially caused by carbon and gunk buildup, try running Seafoam or similar through the system. What engine do you have?
Regarding the shaking at 45mph, does it do that at different engine speeds or just around a certain range? ie, put it in 3rd, 2nd, neutral and if vibration persists it'll be past the transmission, if it only shakes in one gear at that speed it's probably transmission related, and if you rev it in neutral to whatever speed the engine is going at 45mph and it shakes it's engine related. You need to narrow down the problem a bit before starting any troubleshooting.

 

Well I cleaned the fuel injector on the bank that was missing and filled up at a different gas station and it runs fine now.

Still has a ruff idle but it does need a full tune up, not sure how to pull the plugs theres not alot of room.

I just did the air filter and pcv valve for now until I can spend some time doing the spark plugs.


My car kind of jerks back and forth in 4th gear around 1500rpm.