hello,
I did my own timing belt and car drove fine until other day I was doing 70+ my engine light pop on and gave me p0420 and ever since been doing random jerking usually above 60+ mph and sometime after warm start up usually on hot days but it depends like last night it did twice. I already change my spark plug(NGK), i did oil change and coolant levels look normal what else can I check?

 

kay you got the code now google it.

 

It the same code I had over month now and comes on and off
"P0420 Catalyst System Efficiency Below Threshold (Bank 1)"
Never gave me the random jerking even the code was on

 

p0420 bank 1 means that either the primary upstream oxygen sensor is bad or the catalytic converter is bad. the primary oxygen sensor controls the air/fuel ratio of the engine so it definitely could be related. also driving around with a bad primary oxygen sensor can clog and destroy your catalytic converter because of the car running rich on fuel and that would definitely cause your problem. so im guessing that both your oxygen sensor and catalytic converter are bad because you did not replace the sensor when it warned you to do so. catalytic converters are extremely expensive $500-$1,200 dollars the oxygen sensor $100-$300 dollars.

 

Well someone suggested unplugged the o2 sensors and reset the ecu so can default to fuel trim and relearn idle and drive the car around for few days and see if still does it. I did the test and doesn't do it as often goes days without doing it but when does jerk and usually on hot days is small jerk, like today on way to work it did once and not again, when I had them plugged in the jerking happen more often and random especially on hot days. Is weird thou had the p0420 on for while than goes off for while before jerking/started I had this car for two years now

 

you can't drive around with your oxygen sensors disconnected and expect the car to fix itself thats the dumbest s hit i have ever heard then on top of that you reset the ecu so now its really going to be fuked up. the primary sensor regulates how much fuel and air to send to the engine in order to run properly then you reset the idle and fuel trims so now its super fuked. what you need to do is order new oxygen sensors install them and reset the ecu again perform a proper idle re-learn and pray you didn't *** up your cat converter for neglecting your cars maintenance. replace the dam sensors there's no ifs,ands,or buts about this.

 

Right. I gotta get new cat so I'm replacing whole **** anyways.

 

just replace the primary oxygen sensor and see what happens only use i repeat ''ONLY'' use DENSO or NTK oxygen sensors.