Brief History:
I purchased my S2 back in January 06...Fri. 13th to be exact. I noticed there were a few things that needed some TLC, but the important stuff seemed tip top, so the car had 50k on it, but ran very well. I didnt really know what to compair the way the car runs as all the other S2's i drove previously ran and drove exactly the same. I purchased an extended warranty!

Recently I drove the car to San Jose for the weekend, and it ran fine, i even took some of my family members for joy rides. All I have is AEM & DC header. about a week after i returned to SoCal, i was driving a friend to the bank and it was FREAKIN HOT OUT....maybe 90+ that day. We came back to the office and everything was fine, later as i was leaving I noticed the CEL light was on. I didnt think anything much, maybe something to do with the heat out. So i take PCH home and notice that my car is drinking more gas than normal. I reset the CEL when i get home. I stayed gone for a few days, came back the following Wed. on the way to work, then about every 2 days after that. finally it would come back just while idling.

I start researching on this sight how to pull codes, and went in to figure out whats up. First try I got Misfire on 1,2,4. I reset it and changed the spark plugs which looked old and beat, but nothing horrible. I started the car and it ran like a champ, 10 million times smoother than ever, I was losing some major power with those old plugs cause i picked up all kinds of low and mid range power. Its just smoother all around. it seemed great i turned the car off, and back on and let it idle for about 30 minutes, nothing. went inside and went potty and checked the site for some ABS codes i also pulled, after that i went back out to start her up again and after a minute or 2 of idling the light came on.

I checked the codes and came up with a misfire on 3, so i swapped the coils with 2 & 3, started it up and let it run for 45 minutes, nothing. So turned the car off and proceeded to fall into the Flu for 5 days. This was 4th of july weekend. I went back to work on Thurs. I was confident that i had a handle on the problem, as I was make a very low speed U-turn on my street the damned light came back on. i was like F***. So drove it to work, it ran better than ever, and even thought the light was on it wasnt sucking gas like before....Friday i took it to autobacs for an oil change and I asked that they pull the codes. misfires on 1,2,3,4 and a random misfire. They reset it and I drove it home almost 45 minutes with no probs. Yesterday it came back on, So i decided that i would take advantage of my warranty and take it to the dealer. I just turned 61k so im hoping its something fairly simple. I purchased a K&N filter from Autobacs and installed it today. When I removed the AEM it was almost BLACK, I was like whoa. but in all of my reading no one pointed a finger a dirty air filter. So i returned the stock unit to its home and plan to have the OE header put back on. I dont want the dealer to give me sh!t. I also stopped at walmart and picked up a couple cans of fuel injector cleaner, dont remember the name but it was recommended here on the board. So today so far i have changed a filthy filter, and put a cleaner in my fuel system.

I drove around all over south county, and no check engine......YET. I am almost counting on it to return tomorrow. I have read pretty much every post on this, but i have to know.

Going down the list:
I have changed -
plugs
air filter
added fuel system cleaner

I drive aggressively but have never over-revved, or down shifted into the wrong gear. I would like to think i could rule out bent valves or anything like that.

The engine runs great now....it purrs like a kitten, but when the check engine is on (only comes on during idle) I can feel the misfire and the slightly lumpy idle.

How can it run SO great one moment and then like ass another? I have had the car for 7 months and 11k and in the last 1100 mi or so this problem has been buggin me....

WTF????

 

Did you confirm the spark plug gaps before putting them into the engine? What gap were they? You might also consider getting the valve clearances checked and adjusted.

 

When the light came on after you swapped coils, still cyl 3? If you get another light and its still on 3 I would suggest swapping your injector positions and see if that moves the misfire.

 

I did not. They have two electrodes and my measuement tool is round so i couldnt check it before installing. however i was assured that they are pre-spec-ed. where the misfire code isnt there the car runs superbly. I have to put my OEM header back on and i will take it to the dealer for a check up. while im there i will have them install the NGKs that are meant for the motor.

 

I didnt have time on Thur to check the new code, and friday when i took it in i came up with a misfire on all 4 plus a random. so i have changed that filter and added the fuel system cleaner. since about 3pm yesterday it has been running fine...totally smooth. I was expecting it to return this morning, but it didnt, so i might get the light back this evening on the way home. if not then i will wait til it comes back and immediately check the codes.

 

Update: I have driven it to work and home with no incident. is it possible that use of 89 octane acompanied with aggressive driving old plugs and dirty air filter could have contributed to my misfire? So far i have no CEL and under the old cercumstances i would have had it by now.

 

When I had misfires the first thing the dealer did was acuse me of using low octane fuel, this was not the case with me.

 

All sparkplugs come "pre-gapped", but noone should trust this. Always check the gap before putting them into a car. I've never had 4 sparkplugs that were of the correct gap. There is always some variation from sparkplug to sparkplug. They could have been jarred during packaging.

 

I think this could happen. There are so many variables that can produce a misfire. Maybe one thing won't do it, but combining things may increase the likelihood. You really shouldn't be using 89 octane anyway. Run that down or use some octane boost to get through this tankful and then put the good stuff in.

 

thanks Xviper....you are the man!