I've had my S2 for about a month & I'm now convinced that this issue isn't normal lol

Car starts fine regardless of temperature, other than a metallic sound that goes away after a split second, sounds like something inside the engine, maybe the chain getting up to speed?

Anyways, once the idle has settled down to 800-900rpm after the cat heats up the idle seems rough. I can feel the whole car shuttering slightly...through everything. I also get a sort of rattling, seemingly coming from under or behind me...this sound is persistent under rough low idle, it happens when I let the revs dip too low when setting off in 1st gear or reverse from a stop. I also get the same rattle when I turn off the car, as the engine cuts off & winds down I get the same rattle/shudder. Mounts maybe?

Once I drive the car a bit under load the issue seems to go away. Idle is smooth & there are no rattles or noises. Car pulls well up until 8200 & again, after driving it for a bit everything is way smoother at idle.

No CEL, no smoke. Recently did Castrol Edge & NGK Platinums. Neither had any impact on this issue. Almost 76k on the car.

I'm thinking I need to clean the MAP sensor & IACV, if anyone has any other ideas please share! I realize the lower rough idle may be a simple issue but even with a rough idle I don't think I should hear any rattle from the drivetrain.

Thanks in advance for the input

 

I have these exact same symptoms on my car, including the metallic sound at startup. Bump, in for answers as well.

 

150k miles, maybe the fuel filter/pick up tube is abit clogged? You can always upload a video to youtube and share that helps members get a better picture

 

@amsfoto @blackack

"Metallic sound that goes away after a split second"
Does it (only) happen on a cold / overnight start?
Does it sound like: *after the car starts* "GAKKKK!"
If so:
- Starter grind. More annoying than anything else. You will have to eventually replace the starter. But kind of no point unless the starter just dies. I'm at 130k miles and mine does it on 90% of all cold starts.
- The starter on the S2000 is an absolute pain to get to. If you look up a DIY for it, you may agree with me. Also, OEM starters are expensive, and used ones are hard to come by. I'm not a fan of off-brand / rebuilt starters. I'm going to wait until mine completely dies before I get to it.

"Rough idle / RPM dips down really low when coming to a stop"
Does the RPM dips down to 500rpm / last tick mark, and then it sort of freaks out and revs back up to ~1,000RPM?
Does it go away after the car is warm and the idle is stable at 800 - 1,000 RPM?
If so:
- Idle Air Control Valve (IACV). It needs cleaning or to be replaced.

 

Metallic rattle at low rpm could be a broken cat as well

Get under the car and whack your cat to see if it makes funny noises.