Need advice on my engine.
I own a 2000 Celica and my engine has been sort of pulsating/vibrating really hard. It happens when I start the car and the rpm is between 1 and 0 or closest to 0 but when I give it a little gas then it goes away and doesn't return until I turn the car off and back on a few hours later or the next day. It also vibrates when I go in reverse, only when I first start the car though. I'd usually let the pulsating/vibrating go away on it's own but last time I did, the car stalled on me. I've taken it to a few mechanics but they've told me that everything looks fine, except I have a minor oil leak in my engine. I think I may need a new oxygen sensor but I'm not sure. I've also noticed a loss of power sometimes and low fuel economy. If anyone has any thoughts or comments on what may be causing this problem please let me know. As a side note, I got a new catalytic converter a couple months ago, had a tune-up when I first got the car (last September), installed new ignition packs/coils in March, and got a new fuel tank last Thursday.