AP2 Rob

This is my second S2000 and since I have owned it, it has made a "misfire" sound. I'm not really sure how to explain it, when I touch the outside of the car it feels as if the car has a heartbeat. I looked around here and people were saying that it could be a coil pack on the way out, but upon further researching I have noticed that when the car is at idle and I rev the motor a little bit the rpms would rev up then drop below its normal idle and the car shakes then it goes back to its normal idle rpm, so that leads me to believe that the injectors possibly need to be pulled out and sent off for a cleaning. Before I do anything I was hoping you all could help me out. The car has 68k miles on it and its very well maintained, I have never gotten a CEL and when I'm driving the car it runs great.

Benn-O

running into the same issue as well. i got the p1399 misfire code (the vague one) and i swapped the coil packs out and it seemed to fix the problem but, it is still not running a 100 percent, i will swap injectors and see if i can fix it that way...

i'll keep you updated. its a very frustrating problem to say the least and had this happen just 6 months ago. and it was a coil pack.

s2000maniac

my s2k does that too when the car is idling and you press on the gas little bit the revs go and come down to like 500-600 rpm and the motor shakes like its about to turn off but it doesnt and it goes back to normal.

AP2 Rob

Mmm, it's really upsetting, I want to S to run the way it's supposed to be. I guess over the winter I'll take the injectors out and send them in. I don't mind having the car down for a while anyways, thankfully I have a DD lol.

Please let me know if that works for you too Benn!

Supra-holic

Had the same symptoms, here is what fixed my issue:

Clean throttle body/plate
Valve adjustment

Wouldn't suspect the injectors yet, mine are fine at 193K.

Pull your plugs and see which one(s) is missing from a visual inspection.

Other things that could help:
Check plug gaps
Check air intake filter
Check PCV valve

Good Luck

AP2 Rob

I haven't cleaned the throttle body yet, but that I will try that next. I just had the valves adjusted about 2k miles ago. It was doing this before I got the valves adjusted.

I replaced the spark plugs with NGK iridium's and they were pre gapped and they were double checked just to make sure before they were put in. The air intake filter, and the PCV valve was changed around 2k miles also. When my mechanic pulled the coil packs he looked at them and he said none looked to be damaged, but I will visually inspect them on my own for my own piece of mind. If a coil pack is bad, should I just get all new ones or could I just buy one? I just called my local Honda dealership too and for one coil pack they want $76.

AP2 Rob

Anyone else have any input on this?

AlexS2200

Run a compression test and a leak down test to see if your motor is healthy. Then work your way backward.

Read this thread. Explains a lot, even with DBW 06 S2k issues.
https://www.s2ki.com/s2000/topic/889...#entry21061317

NFRAP2

Clean the IAC valve, it's known to cause the idle dip/motor shake issue.

AP2 Rob

Thank you both for the reply! I have yet to do a compression test, but I will do that some time in the near future. I have never over-revved the motor since I owned it, heck the car rarely sees 7k lol. Yes it has had 2 owners before me, one being an older couple that drove it back and fourth to work and my buddy who never really drove it since he had a bike. Now I'm not saying none of those owners could have not over-revved the motor as it is possible since we're all human and we make mistakes, but would the sound of a "misfire" with no CEL possibly be a bent valve? When my mechanic did the valve adjustment he didn't see anything wrong with the spring and retainers, but that was only with the valve cover off. I will look in to cleaning out the IAC valve and I might as well get the throttle body cleaned out too.

From what I was reading though Alex, since the car has never gotten a CEL and the car only has 68k miles would it be best to start with a compression test?