engine hunting/revving up

[integrica]

g'day, my car has recently started reving up and down.
as soon as i turn it on it will rev to about 4000rpm for a bit then down to 2000 and back and forth, does so in gear with the clutch out also, when up to temp it doesnt rev quite as high. problem gradually got worse over a few weeks.
its not throwing any ecu codes
sounds like theres an air leak but cant find one

any ideas?

[chinky]

Sounds like there is a leak. It's probably after the air flow sensor, the ECU reads an airflow that is greart than that reaching the manifold as there is air losts due to the leak. You run rich or lean depending on the leak.

[fatboyz39]

Take off intake pipe. When the car is on, place your hand over the throttle body. If the car idles then you do have a air leak. Just a matter of finding it.

[[ricer]]

on my car the iacv was totally rooted

unplug it and see if the car idles lower again

[rurounix]

It could be the O2 sensor as well

[thepope1986]

O2 sensor wtf?

[B18cEG]

I reakon its the IACV, as [ricer] stated, remove the plug from the IACV and see if it makes a differenct, also check ur manifold vacuum lines, another thing to do is unplug the battery to reset the ecu and leave it unpluged until ur finished, Remove the IACV completely (should be 2 bolto and 2 water lines and a plug) clean with degreaser and inspect seals and unit for any damage, When satisfied re-install connect battery and start it up, If you have a capacitor for your stereo make sure its not feeding power to the ecu through the cars battery wiring otherwise the ecu may not reset.

Hope this helps

Thanks
Jason

[traffic_bird]

Its an air leak, somwhere between the throttle body and the head.

Splash some soapy water around and look for the bubbles.

[croatiaboi]

try cleaning out your throttle body and iacv n see if that helps, if not you could also be ur distributor, i had the same thing happen with my car n it turned out to be the coil in the distributor.

[TBS33N]

if you run a oil coated air filter then you should try taking off the iacv and put some carby cleaner and high pressure air through it to clean the gunk out and you should be sweet! Mine ran fine after!

[NayNay]

mine is doing the same thing. changed a sensor like my mechanic said and it stopped for abit but has started again. i need help with this cos its really f***n annoy'n sitting at the lights in the morning and people looking at me thinking wat a d**k I am for constantly reving my car. lol

[BRacinU]

sounds like an air leak but also could be the PCV valve, which vents the blow-by; a clogged PCV valve will create low rev especially on idle.

[NayNay]

can sum1 help me out and show me what I should be checking? I dont know shit about engines, all I know is that cars should be as slammed as possible!

[JohnL]

Sounds like it may be a gasket air leak in the intake tract somewhere, though it could be a leak other than a gasket, it's just that the fact it's worse with a cold engine and improves when the engine warms up that suggests a possible gasket leak.

My reasoning is as follows:
When the engine is cold the leak is bad, but as the metal (of the head, throttle body, plenum, manifold, whatever it might be) heats up and expands, squeezing the leaking gasket, reducing the size of the 'hole' through which unregulated air is leaking, so the problem is less severe with a warmed up engine.

Could be wrong...

[NayNay]

dude u just nailed it! when the car is cold it does it. but then when warm it stops.

[JohnL]

Maybe, but just because my explanation fits the symptom doesn't mean it's a definitive diagnosis...

[jdmTYPE R]

check the radiator if there is water in there coz low water can course the hunting or try adjusting the screw on the throttle body to much air can make it hunt to....

[beeza]

I would do everything that has been suggested.It's all cheap/free and it will give you great piece of mind to know that is has been checked/cleaned and you car will run better too.