MAVTS2k

Another update...I replaced the MAP sensor and zip tied it down. Ran some fuel injector cleaner. And replaced spark plugs with new NGK Iridium's torqued to 20 ft lbs. I checked the motor mounts, they seem fine.

The problem doesn't seem to be as prominent as it was previously however I am still getting a slightly rough idle when the car is still warming up...For example, I pull out of my driveway and drive about 3/4 of a mile down the road and hit a stop light. The car will at this point be warm enough for the idle to drop to the ~800-900 rpm range but is obviously not fully warm yet. Idle seems to be rougher at this point and almost like a hiccup once every second or so that I can feel in the cabin, but from what I can tell the RPMs are not dropping at all. Leads me to believe this could be backpressure or popping of some kind in the exhaust? I have read that S2000's run rich on startup but don't know if that would cause a noticeable difference in cold vs warm idle feel.

The problem (if it is one) is basically nonexistent once I've driven the car for 10 minutes or so. This is driving me crazy and the only thing I can think of left to do is fuel injectors but can't understand why the problem would only present itself on a cold motor if this is the case.

RolanTHUNDER

Are all vacuum lines attached?

fatjoe10

Do a leakdown test and inspect for slightly leaking valves. In my case, this condition was caused by a leaking valve on #3.

MAVTS2k

Final update...It appears I found the source of my problem. I removed and cleaned the fuel injectors in my garage using a simple setup that allowed me to force carb cleaner through the injector while activating it on/off with a battery. I really should have just sent them out for cleaning but after the long list of other things I tried to do to solve the problem I was not convinced it was the injectors and wanted to avoid wasting any more money. If the problem comes back, I will send them for professional cleaning or just get new injectors.

The car idles better than it did before, no more stuttering/skipping or puffing or anything like that. Hard to say if a professional cleaning would have improved the idle smoothness even further but for now the obvious issue of a slight misfire has been resolved.

Reading the forums it seems these injectors can cause a variety of strange idle issues, some people complained about rough warm idle, but in my case the idle was rough only within the first 10 or so minutes of operating the car. I never got a CEL so the problem was not very severe, which made it tough to troubleshoot. Glad I found the issue as it was really eating at me.

Chuck S

Glad the car is idling better! Hopefully you're through just throwing parts at the car! Old fuel is always a consideration in older, used cars.

Valve adjustment is a routine and simple albeit tedious, back breaking Saturday morning job. Less than $30 for al the tools. Engine must be cold (under 100°F) and even moving it into the garage will heat it over that temperature.

-- Chuck

joelzeller

Glad you found it! I just swapped my ~128k mile injectors with ~22k ones from another S2Ki member. $150 for all 4 used. Solved my hiccup problem! Although, as you mentioned, mine only occurred after the car had been driven and fully warmed up. Wonder why it is the complete opposite conditions with our cars? :/

RolanTHUNDER

Glad you found the problem and solved it! Question is why doesn't the fuel system/injector cleaner do the same thing then? Why did it only get cleaned properly after you took them out and ran carb cleaner through each one? Basically I'm asking why couldn't this just be easy lol. I might need to do this. Looking forward to pulling the injectors though, seems like a fun job

P.S. on a side note, even though hiccups occur at idle only, while driving and pushing hard it runs perfectly fine (which is great). Why is that?

MAVTS2k

In my case, they only occurred when I had the car operating at the lowest possible load. If I had the headlights or A/C on the rough idle seemed to go away. I am not an expert on how injectors work and air/fuel ratios etc. so I can't say exactly why that was. I thought I had read something about injectors showing issues when operating at the "lowest cycle duty" but I do not fully understand what/why this is.

It is possible the Redline injector cleaner would have worked over time but after running a tank through I was getting sick of the problem still being there, and I did not notice any significant change so decided to try a different approach.

I had never removed the injectors in any car before and it was actually quite simple. First thing I did was remove the fuel pump fuse and crank the car a couple times to de-pressurize the system. In my case I did not disconnect the fuel pressure regulator or the other piece with the circle plastic bit on it. I just removed the 4 bolts and 3 nuts holding down the fuel rail and was able to pull the injectors out without removing the fuel rail entirely from the car. I even re-used my old o-rings and seals (which are 150k miles old) because they showed no signs of being dried out.

The cleaning process I used was similar to a couple of youtube videos which show a DIY for using a modified tire valve stem to connect the carb cleaner can to the injector. Did not work as well as the videos showed but in my case it was enough to do the trick.

Car Analogy

Dumping a can of your favorite injector cleaner in tank isn't as effective as carb cleaner sprayed directly into injector. This should not be a surprise.

Injector cleaner is heavily diluted in tank of gas. The composition has to still combust properly and not cause drivability or idle issues. It also has to be compatible with cat over that full tank.

flanders

When you got the injectors out you can reverse flush them as well, often much more efficient.