Engine misfiring and jerking?

Air filter is good. When I got the car the code reader said multiple misfire I put new plugs in it the miss stopped about 75 percent then 400 miles later it came back and that has been 7,000 miles ago. I put new plugs in it last week but it was the same I put used coils on it two days ago and didn't change it.

What about MAF sensor?

I put a new air filter in it it ran fine for 10 miles and the check engine light went out but then right back at missing again. Then I put a new air filter in it and it didn't change (drove it to auto parts store).

After my car warms up, I get an occasional misfire and my service engine light comes on. I had the code read and it was diagnosed as a misfire. I was told to change the plugs/wires. I changed the plugs, pcv, airfilter, ordered the wires and disconnected the battery to reset the service light. It ran like new for a few days, then it started acting up again with the service light coming back on. I still havent received the wire set. I only use bp, shell or mobil gas.

Toyota carolla 99, code p0420, p0300;p0302;p0303.
Replaced ignition coils, spark plugs, gas cap, but stiil I am getting check light for same code

I have recently replaced the pressure plate, clutch, Release bearing, Master & slave cylinders. All was well until driving in fifth the gear pops into neutral especially above 3000 rpm. Been advice to replaced the pressure plate again which maybe weak. The clutch pedal has also become too soft after replacement unlike the way it was, any helpful tips are welcome thanks.

My car was not starting and I had the distributor, spark plugs and wires replaced, I got the car back but in less than a week the car suddenly started shutting off when the car was idled. I took the car back to the mechanic who diagnosed the car and replaced the following parts: catalytic converter, exhaust manifold, amp sensor, coolant sensor, thermostat, thermostat gasket, crankshaft sensor and fuel filter. The engine light was on for almost six months before I took the car to the mechanic. The car is now jerking really badly when I reach between 50 and 60 mph, if I take my foot off the gas there is no jerking, it only happens when my foot is on the gas. Thanks.

I forgot to add one thing which is the car makes a thump noise when this happens and I can feel it when my foot is on the gas pedal.

The jerk feels like a hiccup and feels like the car is lunging forward. I drove the car this morning and could feel this "hiccup" when doing only 30 mph, but when reaching 50 mph it is louder and I can hear like a thump and feel it, when I take my foot off the gas it goes away. The jerk is more like boom boom boom, there is a pause after every boom.