Tacho drops to 500rpm

[quenjose]

Hi all, this is my first post here, so "Hello" to everyone.

Just recently the engine on my dc2r has been acting weird.
When i clutch in to slow down at a traffic light, the tacho drops to 500rpm for a good 2 to 3 seconds before it bounces back to 750rpm. I've also noticed that the engine is running much richer than usual at cold start.

also, this problem i've noticed doesn't happen till the engine is warmed and driven for a while. I've havent done anything to the engine recently so i'm not too sure what it could be. Although i have recently pumped a full tank of mobil 8000 at mobil i dont usually go to. Could it be shit fuel?

thanks
Quen

[JasonGilholme]

could be shit fuel but i doubt it.

Could be your IACV (i think thats the one)

[garett]

do you have a massive stereo or have your lights on when this happens?

using electrical things sometimes makes the revs drop lower
i know when i sit at idle in traffic its ok but if i have the rear demister on or my headlights or both it will go lower and lower. etc

its chewing up the dizzys power

[quenjose]

well, besides just the heater fan blower set to "1" which i normally have on, nothing else really (without the A/C on).


dont have a big stereo either... just a stock 4 speakers n HU...
I just took my head unit out recently as well, and i have not put the new one in yet as i'm still fiddling with the harness. But, i'm not sure if it would be anything electrical as i've had like the a/c on with HIDs back in summer and it was fine. The revs never ever went that low.

Just only started recently... It only happens when i'm just slowing down to idle at a traffic light. The rev needle drops to 500... and i notice the engine is really quiet at those few seconds when its that low... and when i say 500... i really mean that the needle hits the bottom limiter on the tacho... so it could actually be lower than 500...

this could be just me, but i think my exhaust note at idle seems louder and bassier as well

[marky53]

Could be ecu? Or ecu sensors sending mixed signals???? This happened on my old car (not a dc2r), simply reset the ecu and problem gone.....

[quenjose]

yeah thanks marky, might try that tonight and see how that goes...
narrow down the possibilities.

[jimloz]

my DC5 had a similar issue. the revs would go down so far it would nearly stall the engine, then bounce back up to about 1000rpm, and then go back down, up, etc. Honda service said it was the throttle position sensor and replaced the throttle body.

[dynosaur]

my car have the same problem too..... :(

[steebs]

didnt want to start a new thread, but has anyone got a fix for this prob ?

i've got exactlly the same problem cept in a dc5r,
was gonna try cleaning the IACV but noticed a gasket between the IM and TB, didnt want to try just yet until i have a spare gasket just incase.

heres a link i found handy
http://forums.clubrsx.com/showthread.php?t=288936

also to add more info,
went for a drive around the block,
got back into driveway and thought i'd run a few test,..

car is in neutral
- air con on (doesnt matter what setting) -> revs drop to 500 then back up to 700
- lock/unlock doors -> revs drop to 500 then back up to 700

could it be a bad ground by any chance?
or could anything else cause these issues?

i am throwing a CEL but i suspect thats due to headers+high flow cat

cheers,
steven

[DR HONDA]

Disconnect the battery or remove the pcm back up fuse for one minute then let it idle for at least an hour to learn all adaptive values. This may help if there are no engine management issues to relearn all adaptive values and idle.

[[ricer]]

let it idle for at least an hour

just idle in the drive way for an hour?

no driving what so ever or anything?

[aaronng]

Let your engine warm up until the radiator fan turns on twice. Then let your engine idle for 5 minutes. If the radiator fan comes on again, don't include the time that the fan is on in that 5 minutes.

[DR HONDA]

The longer you let it idle with no accesories on the better the idle quality will be. Earlier systems require a good minimum half haour to an hour to learn a perfect idle.

[quenjose]

Well, i dont know if its still relevant now...
but, saw the mechanic awhile back with that problem,
and he diagnosed it as a broken iacv.
didnt replace it.. but just adjusted the bypass valve to keep the revs from dropping so low.

it sort of masks the problem now... like as in the revs dont drop low...
but it always feels like its not idling as smooth as it used to..

would it still make sense to try what u (Dr Honda n Aaronng) suggested?

[beeza]

Clean out your TB.I reckon that's what's causing it.I just had the same thing happen in my Civic.

[steebs]

thx for reply guys,

i've just chucked in half a bottle of fuel injector cleaner to see if it helps, no change.

looks like i should just take off the TB and give it and the IACV a good cleaning + what dr honda suggest.

now question is, the gasket, would that still be reusable or should i just get a new one ?

[DR HONDA]

If the gasket is not torn you could propably get away with it. Also when you reset the ecu do it when its hot so it get a good re learn. Good luck. :thumbsup:

[beeza]

I just used the original gasket.11 yrs old.All good.

[aaronng]

Clean the IACV as well. There is a DIY on it here.

[Samm928]

A++ aaron! would pq but cant =) well called for

[YELLOWDC2R]

could this be caused by faulty O2 sensor?

[steebs]

just an update guys,

i've just cleaned the IACV + TB and took her for a drive, its fixed !
although wen i come to a stop now, it comes down to 1000rpm, for like a split second before goin to 700rpm (alot better than almost stallin tho haha)

ive got the car idling after a ecu reset as im typing this, so hopfully should be ok.

also replaced the gasket too.... just FYI, the old gasket was a bitch to get off, ffs had like two cramps in my hands -.-"

ohh, anyone else wanting to attempt this, dont be a lazy kent and leave the throttle cable attached, i tried to take off the IACV while the cable was attached, and spilt coolant into the engine bay -.-" lucky i put a bag over my CAI pipe ....

anyways cheers to all thos who have helped. much appreciated !

steven