Hey! Glad I found this site, and I hope someone out there can help me with this problem I'm having. Recently, I purchased a 4-1 HP Racing header w/high flow cat for my 04 civic coupe. With the K&N short ram and Skunk2 cat-back exhaust, it really makes a big difference in the exhaust flow, and I love the new sound it makes. After my brother and I put the headers on, we cranked it up, and the inside of my car(especially the steering wheel) started shaking/vibrating when it was idling. It shakes so bad that if I were to try to read what the time is on my watch, I can't read it...especially if the AC is turned on. Sometimes it is smoother than at other times, but it always shakes some when it's sitting still. Then the old check engine light came on the next day. I disconnected the battery for 15 minutes but that didn't do any good. I also reset the ECU, but that was a temporary fix, because it still idled rough and in a day or two the Check engine light came on again. HP Racing did include an "oxygen sensor simulator" and the guy at HP racing assured me the simulator would cure all of my problems. In my town, we don't have a tuner shop, and most of the local repair/exhaust shops don't even know what a o2 simulator is, much less how to install one. I've done a little internet reading, and it seems that the simulator only gets rid of the Check Engine Light, not help a rough idle. Do you think I need to get the Honda dealership to do an Idle Learn Curve on my ride with their diagnostic equipment, or will the Oxygen Sensor simulator cure all my problems? Thanks in advance!

I've got a picture of the simulator on page 6 of www.cardomain.com/id/skunk2civic04 at the bottom of the page. I'll try to post a pic on this site once I figure it out.

 

Alright, I gotta thank God and give a shout out to my homies for helping solve this idle problem. It has nothing to do with that simulator... With the help of my buddies I found out that one of the four header pipes on this 4-1 header was actually coming into contact with my front suspension subframe! This is what is causing all the vibration when the civic is idling! Mike, a good buddy of mine, put the tranny in drive, stomped on the brake, and torqued the engine....after the engine speed got above 1000 RPM, the torque pulled the engine upwards, clearing the header pipe of the subframe, and subsequently there was no more vibration. This makes sense with the symptoms I've been noticing, that is the rough idle that goes away once I accelerate. All I have to do is get this shop next door to grind away just a little groove on the subframe so that pipe will be clear once it's idling. My brother and I didn't catch this little problem when we installed it because it was late in the evening, actually dark when we got through. I love this header, it does an excellent job... it just needs a little love from the subframe to work like it's suppossed to.

 

So what was the deal with the CEL?

 

Ok, let me go ahead and say it, I did something stupid. The other day ago, I thought the oxygen sensor simulator needed to be installed to get rid of the CEL. However, all the shops in town weren't really sure how to correctly install one, so I was getting the color of the wires and writing them down. I had to disconnect the front oxygen sensor to get to the rear connector's wire colors, and when I took it to the shop next door, they told me I just forgot to snap the two connectors back together for the front oxygen sensor!! He said they reconnected it, cleared the CEL, and it idled "smooth" and ever since then the CEL has not showed up again. I know my brother and I connected the 2 oxygen sensors when we first installed the header. I could have sworn I reconnected that front sensor when I got through the other day ago, but obviously not. All I have to do now is get them to grind a little.

 

Right on. So no more CEL. How's that header treatin ya?

 

Dude, besides that vibration thing that's going on, it is awesome. Given, my civic came stock with 127 HP, but I can tell a big difference in acceleration. The high flow cat is so sweet, especially when I put the hammer down on the freeway. I can tell a little difference in the lower RPM range, but it shines in the mid and especially the upper RPM. When VTEC kicks in, my skunk2 cat-back just screams! I can't wait until I get the vibration fixed, because it's like having this really nice new mod, but it's malfunctioning, you know? My gas mileage is better and the exhaust note is MUCH sweeter and louder. Besides that one pipe hitting the subframe, it is one hell of a header.