I usually have to drive my car cold without warmup to make it to school on time and get my parking spot, so usually if i press down the accelrator the car would have a slow reaction of course, but then there would be a loud knocking sound that comes from the direction of my intakes air filter! After the engine warms up I never hear it again, but it really scared me the first few times it happened cause i thought i hit something! IT happens now every morning theis loud knock sound from the left side of the hood. So is this something seroius, or its just cuase the engines cold?

 

I believe the term is called "backfiring."

There's been a rash of this symptom lately (been several threads on this in the last week). Has the engine had a tune up recently? (New cap, plugs, wires.. yada) and have you ever adjusted the AFM?

 

I thought backfiring was only with the exhaust? well ive replaced everything basically but never adjusted the AFM. I just wanted to make sure this wasnt a seroius problem cuase once one bar lights up on my temp gauge the car rusns nice and strong!

 

this isn't contageous is it

just a mixture problem while the car is cold. Check out the air regulator and cold start valve.

 

Speaking of backfiring, is that what these popping noises are from my exhaust when I let off the accelerator pedal, but am still coasting in gear? Is that normal, or is that harming my catalytic converter or anything else?

 

I've yet to come across a Z that didn't backfire while decelerating. It's more noticeable with an aftermarket exhaust though.

 

The accellerating "pre-fire" (backfire is only through the exhaust) is due to a lean mixture while cold. Check your temp sensor/thermotime/cold start valve/throttle vane switch/etc...
The backfire when decellerating in gear should only happen below 2800 RPMS. Decellerating above that the fuel is cut off by the ECU then turns back on at 2800 causing the cylinder to load up with fuel and creat that backfire sound. All cars actually do this, but typically the quiet exhaust muffles the sounds.

 

Ah ok, I wasn't sure if that decelerative backfiring meant I f-ed something up, but good to know it's normal. I mean, it's not hurting anything, right?

 

Enough backfiring and it could possibly blow out your cat but only if it's severe.

I actually blew out a high performance muffler once with no cat installed.

 

does that ever make a sound...holy crap!

 

If you notice when you first crank your car in the morning when its cold, you can get out and depress the diaphram in the egr a little, and it will run a little better somtimes. this is do to the unburned fuel is being re-inerated into the chamber to be burned, but once it starts warming up and the mixture comes to what it is suposed to be it will run like crap with the diaphram slightly pushed.
I had the intake pop when I put my cold air intake on, found out it had to do with my vacume advance believ it or not.

 

i had that poping sound come from my intake too but i think it was the afm opening and slamming shut.......but i also had problems with the car reving up