Rewire

Hey all.

When I first came here I had just bought a new-to-me S2000 only to run into this idle issue that I've seen all over the forums. If i rev the engine and it let go back down to idle, it goes lower than it should down to 500-600 RPM (seen via OBD2 Monitoring) and the car shudders bad before recovering back to 850ish RPM. This also happens when just idling with no load, 850ish RPM down to 760ish and shuddering badly before recoverings.

Things I've done:
- New spark plugs
- New Skunk2 70mm throttle body
- New MAP sensor (measures 0.2-.3 ATM at idle? Is that low? I live at 2500 ft above sea level)
- New Dorman TPS sensor (9% - 90% is the lowest it can go) via monitoring. Still have the old TPS, tested that too, issue still occurs at (5% to 89%) idle.
- Adjusted Idle Screw
- Tightened Throttle Cable and Loosened it. Spec says small amount of slack?
- Cleaned the ICAV 3 times with Carb Cleaner, and bought 5 point impact set to remove and clean the motor itself.
- New Coolant hose for the top end (it was dry rotted badly in several places). Getting a coolant flush done today.
- At least 10 Idle Relearn Procedures via Fuse Reset and Battery Disconnect

Things I've got on order:
- New Grams Performance 1000cc fuel injectors
- New Ignition Coils.

I am ripping my hair out trying to get this issue to go away. Does anyone have some suggestions for something I've not tried that might help with the issue?

Billman250

Cleaning the IAC is a waste.

Cleaning the motor half with anything will likely render it useless.

Freeing up the shaft in the IAC is key.

Re-centering the motor to the valve upon reassembly is also key.

Rewire

The IAC shaft rotated freely when I took the motor off. Felt stuck when the motor was on? Motor is not throwing any errors, would the ECU say if it had gone bad or failed?

How do I center the motor? I didn't do anything special when re-assembling it. There was a little metal tab that wouldn't line up till I made sure the flow was correct in the valve before putting the motor on.

Thanks for the response.

Chuck S

Throttle cable adjustment is page 11-168 in the Service Manual. The free play is specific (4 - 6mm), not "a small amount of slack."

-- Chuck

engifineer

Which way did you perform the idle relearn procedure? After installing the emanage and tune on mine, I tried the one from the service manual (hold at X rpm ....) 4 times with zero success. Then reset it again, started it and never touched the throttle, no loads turned on, and walked away for 15 minutes. Then came back and took it for a drive. Perfect idle ever since. Since then, if I have had the battery disconnected for long enough to need relearn I have done it the same way and never used the procedure in the shop manual. Has worked perfect both times I have done it. Worth a shot since it is free ;p

Rewire

I did the way the manual says to.

Wish there was a way to know if it worked properly other than driving it So frustrating to do all these hours of work only to find out the issue persists

engifineer

Maybe try the start and let idle for 15 minute approach. Others have commented that is what they do on the S2k, it is the only way that seemed to work well for me and honestly that is how I do it on every other car I have ever owned (long idle followed by a long drive with plenty of stops)

Rewire

Still occurring after all the servicing has been done....

Gonna try new injectors and a new PCV valve in the spring......then just gonna take it to the Honda dealer if I've still got issues....

My dream car is not turning out to be much of a dream.....more like a nightmare....

Slowcrash_101

Just to be clear, your car has a hunting idle issue? Does it turn off?? I doubt injectors will help. Idle relearn is easy, just drive the car on the freeway for like 10 minutes. Have you tried a valve adjustment?

Rewire

If I rev the engine while stationary, the car revs then drops down to 400-500 RPM before recovering. When taking off, I have to rev to 2-3 to avoid stalling on takeoff. Can't move at all with the "friction zone" at idle, and even with a small bit of gas, car just stalls out. While idle and stationary, RPMs go from 800-850 down to 700 and the car shudders, before the car recovers back to 800-850, before doing the same thing again.

Happens mainly when the engine is warmed up. Less often when cold.

The only reason it's jarring for me is my motorcycle doesn't behave like this, and neither did the Boxster I owned before. Smooth manuals on those, let the clutch out slowly, give it a little gas, smooth takeoffs. The S2000 it's either I'm dumping the clutch practically to avoid stalling out, or I stall and have to restart the car. No in-between, no smooth takeoffs because if my RPMs are too low, the car just stalls. Very frustrating, and especially embarrassing around town. I've never had to do this much work to drive a manual before.

A total list of what I've done now:
- Cleaned the IACV 3 times.
- New Skunk2 70MM Throttle Body
- New MAP sensor
- New TPS sensor
- New OEM Clutch Master Cylinder
- 10+ Idle Relearns
- Oil change
- Coolant Flush and Change
- Transmission Fluid Service
- Differential Fluid Service
- New OEM Spark Plugs
- Vacuum leak test
- Fuel Pressure test

Previous Owner Mods:
- AEM Cold Air Intake
- Skunk2 Headers
- Skunk2 Exhaust
- Test pipe
- Aftermarket Clutch (no clue what brand or model)

No clue why the RPMs drop below Idle.