I just recently droped in a b16a2 in my hatch, and whenever I start up the car now the rave would idle jumping from 1k to 2k just non stop up n down. it goes away most the time after u drive it for a bit. But just today I relize the idle comes back whenever my car comes to a complete stop even if I drove it for over half an hour. Does anyone kno if theres anything I could do about it??

 

when you come to a stop does this idle happen about twice then smooth out? Cause this sounds like a vacuum leak, that is what mine did. check all your vacuum lines. good luck

 

how does a vacumn leak cause idle to go up and down?

 

Our Honda ECU's use a Speed/Density (RPM/MAP sensors) system to 'measure' airflow into the engine. Take a look at the throttle...when you open it, you are inducing one big *** air leak and it results in an increase in engine speed.

So, in an idling situation, the ECU already knows what it wants to idle at...somewhere about 700rpm usually, and the only way it can do that is through the use of the IACV.

Since you have a vacuum leak (or, a suspected one), engine speed is increased above set idle speed, but the ECU doesn't like it, so it backs down injector on-time to decrease engine speed...but uh oh....theres that vacuum leak again...and so on and so on the cycle continues.

Aside from a vacuum leak causing a hunting idle, having to HIGH a base idle speed will net the same effect. If you removed the IACV (unplugged, this only applies to the 2-wire style IACV, 3-wire is WAY different), the engine 'should' idle on its own, at about 500rpm. This is referred to as the base idle speed and is the speed at which the IACV operates off of. You see, the IACV can only add air, so in effect, there is a window of operation (of proper idle speed) that the IACV can maintain, or wants to maintain, for that matter. If the base idle speed is too high, how is the IACV ever going to bring it back down? It can't...and you could very well get a Code 14 which says "Malfunctioning Idle system blah blah blah", when in effect, its fine, it just can't do it's job properly.

To conclude: ANY additional source of unmetered air entering the intake tract WILL cause engine speed to increase. Base idle speed must be set properly in order for the IACV to do it's job properly.

But aside from 'unmetered air' & the hunting idle, other sensors can also play hell with the idle...the O2, Alternator and even the FITV (another valve, totally mechanical, used to aid cold start-up idling conditions) are just a few that come to mind.