ever since i bought my car, it always had a slight shake when idling. never thought anything of it. it was stock until last week. these past 3 months i've:

seafoamed it
changed plugs
changed fuel and air filter
changed oil twice (did a lot of driving)
installed long tubes (just last week)
regapped plugs when headers were off
!cats and !air
ran open headers for a week
put a y-pipe on today

ever since the header install, i've been getting the obvious codes P0140 and P0160, for the o2 sensors being gone now, but nothing else, just the slight rought idle. well when i was running open headers (just for a week) it would start to sputter at half-throttle, and under full load. felt like it had powerloss. so i thought, ok no back pressure which is why it sputters. i was happy to get the y-pipe installed today, but noticed a bigger change. it still sputtered under load, especially at half throttle just midly accelerating. i haven't checked the codes in a week due to nice long days at work, checked them today and now i got codes 300 and 305, indicating engine misfire #5 cylinder.

also, now when i'm idling at the stoplight or whenever it's stopped but in gear, if i turn my a/c on, my rpms jump up and down from 300 to 700, back and forth, and the car is idling really rough. i just tried swapping the wires for cylinders 5 and 3, and it is idling worse now, and i can hear an audible backfire every minute or so. every few seconds i can hear a ticking sound as well.

plus, i have watched my gas mileage drastically drop since the header install.

sorry for the long story, but i'm curious as to why my a/c will make my rpms adjust so much. it never did that, even when i was running open headers, until today when the y-pipe was installed. i'm replacing a fender bracket tomorrow, so i guess i'm gonna pull the plugs, check them all, and check the wires.

any idea on all of this?

 

bump...

 

Sounds like you may have a couple problems going on.

I would try and attend to the cyl 5 misfire first. Check plug, wire, coil, is pushrod bent, etc. If you delete the code does it come right back or was it a one time thing?

The P0300 could be a few things of course. Judging by the reduced power, bad mpg, sputtering, backfiring, I would think it might be a front o2 sensor. Are your pacesetters coated? Often the coating is notorious for killing an o2 for the first few weeks you run them. I had both o2's go from that. Never showed an o2 code - just P0300. Have access to a scanner where you can see how the o2's are moving around?

You probably also could benefit from a good tune at this point.

 

no they are not coated. the 305 code hasn't come back yet, but i got the 300 to come back after a couple WOT runs. i'm waiting for 305 to come back on, or maybe the code for cylinder 3 since i swapped wires.

i did however extend my front o2s since i managed to somehow forget to buy extensions, so i wired in about a foot and a half of wire to them, tested them using a multimeter and each connection was good. i keep looking under there to see if the wires are melting and they are not. everything is still good from what it looks like.

the only scanner i have to use is a DTC scanner, nothing fancy. i will check to see if the shop has a scanner tomorrow when i go in to fix the bumper.

what do you mean by the coated lts kill them? like melt them or what?

 

well in the news today, i pulled spark plug for #5, and that sucker had a chunk missing out of one side, and a hairline crack on the other. guess that explains why my car wasn't doing so hot... will post pics up when i get done.

 

here's the culprit:




guess i never thought that when i put the headers in, i remembered having to push the driver's side in decently hard and it slipped in. i guess it hit the plug on the way up, and i never noticed it. runs like a champ now!