Hey guys, lately I've had some issues with engine stuttering. A few symptoms
1) Almost every time I come out of gear my RPMs drop to 800-900, the car shudders, and it jumps to 1200, then back to normal idle of 950-1000.

2) Very occasional stalling. (Similar to 1)

3) The car will just drop power. 1st, 2nd, 3rd gear, doesn't matter. Usually for not more than a tenth of a second, but can sometimes be for an entire second. It even happens in cruise control. I recorded it to demonstrate:
Update: recording of shuttering idle, and engine COMPLETELY unresponsive to throttle input:
Update 2: I realized that #3 almost ONLY occurs at 3600-3800 RPMS. I used to have a small rattly sound at this RPM, as well, but couldn't nail down what it was before it went away. It sounded like it only came from the passenger/exhaust side of the engine bay, and underneath, so we assumed it was a sort of resonance with the exhaust system.




Does anyone have any ideas? I swapped the spark plugs, cleaned the injectors, checked the Accelerator Pedal Position Sensor, but I'm not sure what's wrong.

Thanks in advance!

 

Any CEL codes?

 

I used to get an occasional cylinder 1 misfire. I tried to swap coil packs (no effect) then swapped injectors. I can't say for sure if I didn't have this engine hesitation problem before, but I definitely have it after.

 

No O2 sensor CELs? Check out this link:

https://www.s2ki.com/forums/s2000-un...no-cel-405270/

 

Unfortunately, I've never had an O2 CEL.

 

Spark plugs are in good order? Try a MAP "whack?"

 

Spark plugs are brand new, but I haven't tried a map whack! Hopefully we get somewhere.

 

What plugs? Torqued to 22-24 lb-ft? (Grasping at straws here.)

-- Chuck

 

Unplug your battery for a little bit to reset your ecu. When you reconnect your battery and the car dips to a low idle do not give it any gas, it is a learning ECU and will correct itself on it's own. Drive the car around for a little bit, again do not give it as gas when the idle dips. If you've tried this and the problem persists, then try cleaning or replacing the IACV.

 

Update: when recording the idle dropping low and stuttering, about halfway through the video the engine became completely unresponsive to the throttle for over 5 seconds. Then, and audible clunk is heard from the engine and throttle response is restored.

https://youtu.be/0O-DDwkQI4s