My gs300 2001 back fires and has some misfire i went to the mechanic he told me to change spark plugs and coils.
I changed the spark plugs and coils and also changed air filter
But still back fires and misfire.

 

What codes are are showing???

 

Fire your mechanic. You could have jumped some teeth on the timing/cam belt. Check your timing. I just have to say that I have never heard of this issue on a Lexus before. Backfire to my knowledge is caused when the intake or exhaust valves are open and for some reason, fuel and spark is sent to the cylinder. Hence the intense sound and pressure generated. It can definately destroy your engine. I'm going to follow this one.

Paul

 

I'm assuming your car starts and runs fine, before my current problem my car wouldn't stay running or would rarely start, had a misfire in cylinder 1 and 6, turns out it was the crankshaft timing gear. Starts up everytime now, just can't get my charging system fixed 😒

 

My mechanic said it could be coils,plugs,maf sensor i have changed all of them but didnt got fix so I decided to check the vehicle myself and I found the problem it was leaking fuel injectors.
The nxt day i bought the injectors and fixed it myself and it works now no backfire no missing

 

Outstanding! I will put that one in my back pocket for the next timke this happens to someone else. Thanks for getting back to us.

Paul