Dodgy idle & low rpm hesitation
 

Hi all,

Got an issue with my S2000 and was hoping you guys could help me with it.

My S2000 ever since I bought it (6 months ago, approx 5k miles) has a bit of a lumpy idle, coming to a standstill it will often drop revs to the point where it stalls. If I then start the car again it'll idle happily (albeit a little lumpy still) until I pull forward and stop again at which point it will stall - rince/repeat.

When I first got the car it was throwing a secondary lambda warning, replaced that at which point it started showing another warning for Catalyst System Efficiency Below Threshold. Have ordered a sports cat to replace the stock cat anyway so waiting for that to be delivered. It was then fine other than that warning and the stalling until recently when it's also recently started showing an extra EML for the knock sensor (possibly a bit before the hesitation mind)

The past couple of days it's developed a hesitation between 2-3k as well, might be due to the heat but not ideal.

I've replaced; Spark plugs, map sensor, second lambda and given it a service.

Anyone got any ideas where to look next? Throttle position sensor is reading between 12.2% and 96.5% which I'm led to believe is broadly right although the top end might be a little high?

Thanks,
Alex

Update (28/07/17)
Replaced:
ICAV,
Map sensor,
Spark Plugs,
Both lambda sensors,
Catalytic converter

Issues/Symptoms:
Still got dodgy idle & random low rpm hesitation, also needs throttle on cold startup or it won't catch
EML giving a Knock sensor error
Exhaust is blowing at the leading lambda port

I've got just the thread for you :) https://www.s2ki.com/forums/uk-irela...g-idle-808050/

But next I'd go with Idle Air Control Valve (IACV) cleaning followed by coil pack checking/replacement

Did you replace with OEM spec bits?
Have you cleaned the IACV and the throttle butterfply?
Why only the second lambda - IIRC these should be done in pairs

Sorry forgot about the ICAV I removed and cleaned it, wasn't very dirty at all though implying previous owner had maybe tried that already.

Map sensor was a genuine item, lambda sensor was from Eco Lambda, Suppliers of quality economically priced lambda sensors by post.. who I saw people recommend on here. Did wonder if I should try replacing the primary and see if that makes a difference.

Coil packs I did think of but would've thought if anything that would be a problem presenting itself at higher revs more than lower? Is there anything that can be done to check those, also would've thought an individual coil pack would throw a specific cylinder misfire code?

Did think also about valve clearances, I've got the tools but had to finish fixing the Noble so I don't need to drive the S2000 and it can be cold to do the adjustment :)

It won't be able to tell you if there's a misfire if the knock sensor is out/incorrectly torqued plus it guesses at which cylinder has the misfire most of the time, then gives up, and will tell you it's "random misfire" even if it's only one specific cylinder :)

See the other thread I linked to above for MB's comment on primary lambda replacement and where to get them from.

I just bought both primary and secondary from Rock Auto here. Part numbers are : DENSO 2344124 Honda Part No:36531PCX014 (primary) & DENSO 2344601 (36532P8AA01)

Coil packs are harder to diagnose, when they get bad enough they will cause a CEL. I think I have 2 sets here at the moment, one set is old OEM and the other is a non-OEM set of coil packs.

The secondary lambda has no influence on fuel control so don't bother with that unless it's showing a cel.

The primary one is the most likely candidate for poor idle / hesitation, and pooor fuel consumption.

Also strongly advise not buying blueprint lambda sensors - only use OEM.

Coil packs don't cause hesitation issues normally, it's more misfires.

Try the idel relearn procedure https://www.s2ki.com/forums/uk-irela...learn-1051596/ it worked for me.

Check fuel trims
from my experience on a different Honda model, that efficiency code was an exhaust leak

How would you do this and what could you do to rectify?