I recently change my spark plugs to the ngk 2 step colder plugs and changed from my 42lb injectors to 60's and a tuned pcm from zzp. I had a random misfire p0300. I then put my stock injectors in and got a p0303 code, misgire in cyl 3. I bought all new spark plugs to diagnose them. still getting the rough idle where the rpm's are going up and down. any suggestions on what it could be???

 

put your 60's back in?

 

I had the same problem, but i didnt change anything. It was a month after i got the car. Piston 3 misfired. Dealer didnt do anything for it. Just told me if it happens again to bring it in. and it hasnt happened since

 

they are in, i had 42's and sold them and got 60's and they are installed

 

Okay just making sure you didn't leave your stock injectors in like you stated.

The rough idle could be a dirty throttle body. A random misfire hasn't been an issue for me. I've had the code once or twice, but I think I'm getting mine from the WOT box.

 

so i should clean the throttle body huh

 

Try that first, then check spark plugs and gap. After that the searching can get tougher.

 

is the code still showing up???

 

the code is still showing up and has a very bad idle. It acts as though the car is revving up and down up and down. I bought new spark plus that don't need to be gapped. E3's.

 

Our cars HATE those spark plugs..

there was just a thread on here where the entire tip of the spark plug blew off.

Check your throttle body, that has a large issue with causing a rough idle.

misfires happen all the time at idle or downshifts.. seems to be the norm.

 

I'm gonna go and clean the throtle body now, maybe even clean the air filter on the aem because I haven't done that since I got it about 37k miles ago.

 

That could be the problem too...

mine was roughing horribly, i cleaned the TB and it completely stopped...

 

but did it throw a code (p0303)

 

yup.

everytime i go to autozone i have em check my codes.. i normally have a misfire.

What you do is change the coil packs around... if the misfire is in three, change it with cyl 2...

then check your codes...

if its a bad coil back, youll see the misfire in cyl two, instead of 3.

 

is the throttle body inside my wheel well?

 

... no...

the throttle body is whats connected to the supercharger.

That the intake hooks up to.

 

the metal part with the big metal valve that you can stick your hand in and move?

 

Yup. Clean the inside of that..

try not to move that thing too much... i mean, you have to in order to clean it, but just be careful.

 

definetly was really dirty. cleaned it and waiting to see if that fixed the problem.


nope, still revving up and down.The rpm's don't show it but you can hear it

 

the rpms dont show it?... but you hear it..

what??

 

you can hear it through my loud exhaust that the engine is going up an down slightly not a lot. when i drive and come to a light or stop, then you can see the rpm gauge flicker up and down. sometimes it sounds and feels like it is going to stall. could my car be running too lean or maybe a bad injector??

 

Is the pcm tuned for 60's?

 

It should be..

 

It's really hard to get a perfectly smooth idle with 60 lb injectors no matter how good the tune. Mine fluctuates all the time too. Sounds like there might not actually be anything wrong.

 

yeah, I bought a tuned pcm from zzp and the injectors. Problem is that I am getting a cel with a misfire and the rpm gauge is fluctuating up and down. Sometimes seems like it is fuel starved. Are you guys getting better fuel economy with the 60's and custom tune vs teh gm stage 2?? I am getting like 4-5mpg with the 60's with the custom tune!!! i used to have the gurggling exhaust when letting off the gas or down shifting. I don't have that anymore. Am I running too lean??