I posted a message about Engine Misfire last friday,

yesterday the same situation came back again.

I was driving my car with a/c off for about 20 minuts and when I switched on my a/c,before I came to a stop sign, but when I came to a complete stop, the car misfire.

last time is because I keep the car idling for 5 or 10 minutes with a/c on

( the weather is very hot these days and both of them happened around 2 to 3 PM)

I push the tranny shifter back to parking position and restart it, and switched off the a/c and everything is ok now.

I opened the hood today, and checked there are some coolant leaked from the extension tank cap, not a lot of,and now it is stopped leaking,

the coolant level is a little bit low, near MIN mark.

the car has another problem: it's radiator's upper neck(which is connect to

a hose to engine) is cracked, so I moved the hose upper toward the neck bottom, but there will be some coolant come out from the connection.

this leakage has been found about 2 months ago.

What do you think about my car? is it due to the bad radiator or engine overheating, or even bad thermostat?

some one told me it is because the bad RPM sensor? what's that?

I need your help badly, it is too hot here, the sun will burn me!

Thank you.

Lux