Bouncing tach while idling

[shakil]

hey guys!! So i Just got a zc swapped into my crx and what the problem is when it starts to warm up after im driving from street light to street light i put it in neutral gear while coasting to the next light, the tach needle seems to drop down and below around lets say 500rpms, which then feels like the cars wants to die but it never does and it brings itsself back up abve 1000rpm and continue bouncing lesser n lesser until it calms down to about 8-900 rpm semi-smoothe idle. Can anyone explain why this happens?

[sh0ko]

my car does that too .. only happens when its friekn hot as hell outisde though

[mo_money2supe]

I've heard the same on Integra's before; ended up being a vacuum leak, so I would assume it's the same thing for yours.

My car's also having the same problem right now, but it's 'cause my TPS sensor's having problems. Maybe look into that as well? However, I am throwing a code, so that'll likely not be the case for you.

[zain123]

shak i got the same shit hapenin
when u figure it out leme know lol

[AE92_TreunoSC]

It sounds like its surging. If you have air in the system (from not being bleed properly) air in the throttle body will cause it idle erratically (at least thats what my experience has taught me, its just a guess)

[LilDrunkenSmurf]

Should be a vacuum leak... I had the same problem in my accord (bounced 1k-2k rpm in idle)

[shakil]

well I thought it was the coolant system, i tried bleeding it with the bleeder screw but it didnt do anything lol. i could literally unscrew the whole thing off the engine and it wouldn leak a thing. So any suggestions of how to bleed the coolant of air any other way? I thought it was coolant but a vacuum leak sounds legit as well. I'll look into my old hoses of course!! anyways bump if anyone else has suggestions of any trouble shooting

OH... and my ecu isn't throwing any codes except for my O2 sensor.

[rc2002]

Originally posted by AE92_TreunoSC
It sounds like its surging. If you have air in the system (from not being bleed properly) air in the throttle body will cause it idle erratically (at least thats what my experience has taught me, its just a guess)

Air in the cooling system you mean.

It could be a hundred different things. My money is on the IACV. Try taking that off and cleaning it. Check for vacuum leaks around your TB and IM gaskets. Try letting your car idle with the rad cap off to try to flush out some air bubbles in your coolant.

[AE92_TreunoSC]

I was on tylenol 3 when I wrote that lol

I see it a lot with V6 hondas especially if theres air in the cooling system (in the heater core or the Tstat housing) it'll surge once it pressurises. (5 mins of running) I would almost suggest a coolant flush, and clean out all the shit in the cooling system. But its just what I would try first before trying the IACV myself, I would try that after addressing the fact you have nothing comming out of bleeder screw.

[XRracing]

had the same problem in my teg and it ended up being a vacum leak

[SILVIA.K]

This is all it can be start at the timing it will fix that if not it can be a faulty spark plug.
faulty spark plug wire or ignition coil or fuel filter or vacuum leak if that does not fix it .