It is with the throttle screw adjusted. But it does tend to hesitate and buck in low rpm. Also juddering a little at idle (+- 900rpm)
Still popping exhaust when idling cold, even with cat in place.

It's not as smooth and responsive as it used to be.

It only drives good at more dan 1/2 throttle and at full throttle.

 

Finally it popped a CEL!!!

Changed the oil today (previous owner had 0w60 for track use... Now 5w30)

During testdrive the CEL came on with codes p0170 and p0172, system too rich.

 

It's been a while... and still no news.

It's at the dealer right now for the 2nd time.

The first time they couldn't pinpoint the symptoms to 1 problem, so they decided to wait for an early (2001) S2000 to come in so they could change out the throttle body, IACV, and such.

All that time I've been driving the car without any problems, it was actually still pretty good to drive. Not as nice and smooth like it used to be, but still very doable.

Last week they finally had a car to experiment with, so I took mine in and waited for news.
Then I got a phone call telling me they found the problem and tracked it down to my subwoofer. As soon as the subwoofer was disconnected, the problems would stop. They tried switching over everything from the other car without result, untill they noticed my subwoofer.
I was a bit skeptical, but it might be a possibility.

When I went to test the car, I immediately knew the problems wouldn't be solved...
They confused my explanation of "popping from the exhaust when cold" with the popping of the subwoofer when the airpump kicks in.
They were very proud to show me it didn't pop anymore when they turned the radio off.

I was even more proud to show them how the engine still wasn't ok.

So they've wasted an entire day swapping out parts and checking for the wrong symptoms....

Now I remember why I don't like to visit dealers...


Anyway, they were going to do the whole swapping out thing again, this time while checking for the right symptoms.

I also asked them to test the injectors. The previous engine dropped a valve and the broken valve stem went into the intake manifold, possibly hitting the fuel injector.

Don't know if a damaged fuel injector would cause these problems?

 

And still nothing, the dealer pretty much gave up.


Had all 4 injectors tested and they were perfectly fine.

 

Keep us posted. I'm having what seems to be kind of the same thing. On mine, if I keep it at 4000 rpm, it will stay like 3-4 seconds, then slight misfire starts and rpm drops to 3500, then the next second back to 4000 rpm.
It also does it at idle, and based on my scans, the trouble starts when the fuel trim goes over -20, at about -26 it gets fuel then everything ok. repeat again and again


I ran fuel system cleaner, changed the IACV, nothing.
I am planning to change injectors with another s2000, after that, valve adjustment.
I'll let you know if I find what the hell is wrong.

(it doesn't bother me too much, as it only does it when I'm keeping the rpm constant, and that doesn't happen very often during short city drives)

 

Well, I also have those rpm drops if I try to keep it at a certain rpm. Isn't very noticeable during driving though, except at around 2500rpm city driving. That's horrible.

I think my problem is also a bit worse since the engine will actually stall when returning to idle. I've now adjusted the throttle position from the standard 5.9% to 6.7%. At least it won't stall on me now and is a bit more driveable.

 

If it helps, in 2 weeks I'll be taking it to a mechanic who has worked on several s2ks. He has also worked on a new GTR (tuned to 1000+ hp), right now he is working on a wrx sti in the shop. He's actually an ex honda mechanic that got tired of the bullshit he had to go through in the dealership - and opened his own shop.

My car also had the engine swapped by the ex-owner.
mods that may be related: big bore throttle body, fidanza flywheel, walbro fuel pump (and maybe port and polish intake - we will have to inspect that)

He checked the vacuum, saw a ground has been relocated and isn't happy with how my wires are. he also says the car should start quicker and we'll look into that as well.
We are going to take off the ecu->engine harness and work on it, as well as trying to find out the original problem. I will keep you posted.

 

I'm curious to see what he will come up with


I was wondering if titanium valve retainers with dual valve springs could cause these kind of problems on a standard ECU?
Standard steel valve retainers use single valve springs. The previous owner had titanium valve retainers installed with dual valve springs, in combination with an AEM custom mapped ECU....

 

Mine had unichip set up for nos. That blew the previous engine.
No idea what valve retainers/springs I have, but I think they are stock. I'll take some pictures this weekend if the weather clears up to let me do the valve adjustment.

 

i'm not sure if someone has mentioned this yet but check the throttle cable. Also don't get on the throttle when the car bogs down, the ecu is a learning ecu, it will adjust itself