revving up and down (hunting)

[mickmdc5]

Hi all
I was having trouble starting my car after heavy rain one night,now I have finally got it running but it is hunting while it idles (revving up and down between 1000 and 2000). it was sitting up for 5 weeks so I took it for a good drive and its still doing the same. I also cleaned the icv sensor and that did nothing either. Someone suggested that the trottle position sensor could be an issue but i dont see how as it runs fine while driving just wont idle steady when stopped. Any ideas please??

 

[colinged]

Hi Mate,

I've had the hunting issue every year I take the car out the garage from the winter (battery disconnected). I got help from a friend to take everything apart and replace wiring and clean iacv etc...I then found the service manual... In my case it's solved by doing the ECU learning procedure. Possibly your issue too if it was sitting up for 5 weeks..maybe, worth a try anyhow.. Good luck holding the revs! ;o)

Cheers,

Colin

 

[C&S Evo7]

clean the iacv, look for leaks and reset the ecu, just because you have cleaned it once doesnt mean it is fixed, the stepper motor itself could be screwed,

the reason it hunts is because the fuel and air requirement for he engine cant stabalise when at idle,

when the throttle plate is shut no air would go in and the car wouldnt idle,
so on old cars there was an adjustment screw, this allowed a little air in so it would run and would adjust the idle speed.
, move on a few years and with the invent of lots of electrical accesories the load on the engine changes continuously as stuff switches on and off, (the alternator charging causes drag which causes the load which needs the engine to speed up or slow down, of course we dont want the idle speed constantly changing so a throttle plate bypass system was introduced , the base idle speed can still be set with the screw but so now to maintain the same idle speed when the demand changes a little more air is needed so the Iacv moves a little allowing a little more air past the throttle plate without actually opening ,

now what happens when its hunting is normally due to the iacv not moving smoothly, the car drops to idle, then the ecu says pick up the speed so tries to move the iacv, it cant or its stiff, then the ecu detects the change in engine speed so reduces fuel , so basically you get stuck in this viscious loop of the ecu trying to compensate for the valve being stuck.

while this hasnt always been the problem, for 99% of cars that have the hunting issue its the iacv thats caused it, it is very unlikely to be the TPS , generally the honda sensors themselves are very reliable, and other than the lambda dont fail unless they havebeen messes with

 

[SharpyDC5]

Mine did this aswell.... I changed the lambda sensor. never came back.

 

[davidpingu]

clean the iacv, look for leaks and reset the ecu, just because you have cleaned it once doesnt mean it is fixed, the stepper motor itself could be screwed,

the reason it hunts is because the fuel and air requirement for he engine cant stabalise when at idle,

when the throttle plate is shut no air would go in and the car wouldnt idle,
so on old cars there was an adjustment screw, this allowed a little air in so it would run and would adjust the idle speed.
, move on a few years and with the invent of lots of electrical accesories the load on the engine changes continuously as stuff switches on and off, (the alternator charging causes drag which causes the load which needs the engine to speed up or slow down, of course we dont want the idle speed constantly changing so a throttle plate bypass system was introduced , the base idle speed can still be set with the screw but so now to maintain the same idle speed when the demand changes a little more air is needed so the Iacv moves a little allowing a little more air past the throttle plate without actually opening ,

now what happens when its hunting is normally due to the iacv not moving smoothly, the car drops to idle, then the ecu says pick up the speed so tries to move the iacv, it cant or its stiff, then the ecu detects the change in engine speed so reduces fuel , so basically you get stuck in this viscious loop of the ecu trying to compensate for the valve being stuck.

while this hasnt always been the problem, for 99% of cars that have the hunting issue its the iacv thats caused it, it is very unlikely to be the TPS , generally the honda sensors themselves are very reliable, and other than the lambda dont fail unless they havebeen messes with

This has been answered so many times now. I've even seen similar replies from you many times before Simon but this is a really good descriptive breakdown of the way it works (the best I've seen you write) and why perhaps our cars suffer more than most.

A suggestion if I may would be to put these comments in a sticky somewhere. "Sticky: Sticky Idle" :xlol:

It's definitely a very common issue with the way this system works though and most of us have suffered from it at some point. I can guarantee whenever mine sits in damp conditions for more than a few days I'll get issues but since I fully stripped it down last year a warm through and a good blast seems to get everything working well again.

A couple of helpful points to people to help reduce symptoms:

Make sure your air filter is as clean as possible. A closed air box seems to give me less issues than an open design did. I think the closed filter design tends to take it's air feed from a little higher up than your average CAI and I think that the air that a closed filter design is pulling through will generally be cleaner than a CAI which is more on level with exhaust fumes from other cars and oily spray in the wet.

Lastly, I haven't figured out exactly how it works yet (you can maybe help me with this Simon) but there is some sort of exhaust gas recirculation in place through the inlet manifold and thats why if ever you strip the inlet and TB down that's done a fair few miles it will often be full of gunk. That gunk WILL get in to the TB and cause issues. If there is a way to bypass this re-circulation in some way you'll have a cleaner inlet and I'm sure that 90% of these problems would go away.