Rep Power: 512

I just noticed that my car has a kinda rough idle.. recently, my car's been throwing random p030x codes (misfire on x cylinder), and I've had a locked in 420 code (my kitty is dying, it's on my list o' **** to buy). Both o2 sensors were replaced within the last 3 months, AFR being read on my AEM UEGO has been happy. Engine temp's normal, no smoke, plugs look happy. Just did a valve clearance adjustment a month ago, and it ran smooth after I did it. Everything was torqued down properly. Gas mileage shitty, but tolerable (~28-30 mpg average). Need to take her in for a timing belt replacement still. Stealership gave me a $650 quote for the timing belt/accessory belts/seals replacement package. >_<

That's all I got for symptoms. Any takers? lol

for those that don't know what I have by now, 2002 ex coupe. AEM V2 intake, kamikaze header, random tech cat, apexi ws2. 120k miles

 
Rep Power: 208

You could start with normal tune up stuff...Clean injectors, fuel filter could cause that and they are cheap to do.

Is it just one piston that's misfiring, or all of them?

 
Rep Power: 512

I don't scan on a daily basis, so the spurious misfires always get logged, so I'll see spurious misfires on all 4 (P0301-P0304) along with the "misfires on multiple cylinders" code (P0300)

I regularly use STP complete fuel system cleaner, probably once every 1-3 oil changes. I also hate the fuel system on the 7thgen. If I'm not mistaken, the fuel filter is part of the fuel pump assembly..

Oh, I also get a random P1457 (evap system leak) code. Very, VERY sporadic code, only get it every once in a while, but I've seen it enough to make me go "wtf"

 
Rep Power: 208

Check your vacuum lines and around evap. And change that fuel filter if you haven't, it is a often neglected part and can cause idle/power issues, it also clogs quickly if you use cheap, dirty gasoline.

 
Rep Power: 512

I'll definitely check it out. I'm very picky about my fuel, usually only filling up with Shell and Chevron if I can help it, and meticulously using fuel system cleaners. I should just go around with every vacuum line and replace them all.. hell, 120k miles is enough to justify it, right? lol

 
Rep Power: 208

^ It couldn't hurt.

I would hunt down that evap code first.

Also test to make sure you got good spark just cause it's free and takes a whole 2 min.

 
Rep Power: 512

I know I got spark.. definitely done that test more than once. That evap code, like I said, if VERY sporadic.. I've seen it probably 5-7 times in the last 3-4 years. Just enough to make me google it and keep an eye out for it. I have a troubleshooting guide for it, but it requires tools I don't have, like vacuum gauges and whatever.. I think... It's been a while since I took a look at it.

 
Rep Power: 234

Poor man's test: Get the car idling, then carefully spray carb cleaner (the same stuff you cleaned the TB with) on each line and when you hear the engine surge that's the line to replace.