I have toyota corolla 98when i stop at stop sign or signal i have to give hard accelerator ,it also shakes when it is stop , i got my spark plug and gasket change problem reduces but still i have to give accelerator hard many times what would be the problem my check engine light blinks most of the time i have to give hard accelerator

A flashing CEL indicates a more serious problem than if it is steady on. There is so much guesswork here I recommend an OBDII scan asap. You will probably have a P0300 code, probably with P0301, 0302, 0303, or 0304...which is pointing to which cylinder is misfiring. Or a vacuum leak, MAF, and so much more. Many parts houses will scan it free, but if you can possibly wait, don't but the first thing the guy says. Electrical parts can not be returned, and I sure would hate to have you buy something you don't need. bring the codes back here, in a new question so we will see it and myself or one of the guys will be happy to help you from there

P0302 , P0135, P0420 I should to mechanic and he told me spark plug is burnt out and oil is into engine he changed spark plug and gasket and it's is working fine but it gives this wired thing some times not always. Also as per him OBD II shows this codes now also but it should go in day or 2 but don't know what is problem

P0302 is misfire cylinder #2. Very well could be plug, but injector also. P0135 is o2 sensor (says bank 1 but it only has 1 bank) and that's a heated o2 sensor, so the sensor itself may not be bad but the wiring to it, the connection. 0402- Catalyst issue. And that make perfect sense from what you describe, your catalytic convertor may be plugged or worn out. The problems you are having fit right in to that. http://engine-codes.com/p0420_toyota.html

But what about this 'oil in engine'? In the coolant? And what gasket? I'm pretty sure you have the 1.8L 1ZZ FE.. just didn't have variable valve timing (yet).that engine first appeared in '98 but not ALL Corollas had it, depends on date, to the day, of manufacture. Toyota did some really odd stuff, like put a new line of Corollas in showrooms in March of 2002 and called them 2003 model year

mechanic told me that because of spark plug oil is accumulated into the engine etc ( i do have to do oil change every 3 months and usually there is not much oil left )

so should i change my catalytic converter??? or the problem is becasue of something else

What's the mileage? I don't get that...unless you have bad ring(s) and oil is getting past in to chamber, but the plug it's self won't cause that, more often a weak coil. The 1.8 does have coil-on-plug now, and has for a while but not sure if it did then in '98. OR really cheap plugs. Denso is the only plug I will ever use in my Corolla

I don't want you to buy a new cat on my say-so, but I can say that all signs point to it

I didn't put that quite right...the misfire can cause oil to collect in chamber, IF it's getting past rings and not burning off... but not necessarily the plug. And don't wait until oil change time if there is not much left..keep it where it should be in between, add as needed