4AGE (AW11) Random and erratic hunting idle at running temp.

[worldwalker]

I'm sure this has been covered but really struggling to find a result from the search.

4AGE redtop, once up to full running temp (90deg) is randomly hunting after being static revved (pulled up as roadworthy item).

I've replaced all the vac hoses except the TVIS hoses under the manifold and cleaned and resealed the TB. There was an issue with the RPM not settling back to idle and the BVSV remaining open after revving the engine, it would require the butterfly being pushed to closed to get the RPM to settle and close the BVSV. This has been resolved (somewhat) by adjusting the TPS; The RPM now settles and the BVSV closes but there is still a dip in RPM before settling. I have a feeling this problem may be related to the hunting.

The hunting issue seems to crop up after the engine is completely warmed. From time to time the RPM will begin hunting around idle (800+-200RPM) and once it starts continues until the engine is revved. The rate of hunting and the trigger varies, sometimes it will begin on its own, other times it requires a descent race of RPM and the frequency of hunting varies randomly, from 1hz to 2hz.

I've tried removing various hoses during the hunting and sometimes it stops it, other times it does nothing and some hoses change the frequency of the hunting. I've tried the workshop manual but short of replacing all the valves I'm at a loss as to where to start. I'm really looking for an easy fix and not fused to the longevity of the engine as its going once its licensed. I was hoping something simple like blocking off some of the emission valves might be a way around it as a temporary measure.

Any advice, tips or tricks would be greatly appreciated.

Nick.

[dumbass]

i do recall many years ago working on these that they were
a pain in the butt to bleed the cooling system so
maybe there is an air lock which i know can cause hunting
problems sometimes if u have air in the system

[worldwalker]

Ah yes, well the system was previously bled but poorly and I didn't do a great job myself (after cleaning the TB and cold idle valve). I was getting ahead of myself checking other things while the engine was running and forgot to rebleed after running. The top hoses are blistered and leaking now anyway so I'll have to replace them and rebleed again tomorrow.

Is there anything else I should grab while I'm out? I know there will be a simple write up on it but I may as well ask, is there a quick way to disable the TVIS by bypassing some of the vacuum lines?

Thanks again.

Nick

[dumbass]

to bleed the system in mrs2 we used to jack the car up at rear i think to get a better angle
and get radiator cap higher than rest of motor
or park car on step driveway

[BLSTIC]

I had a similar problem in a Prelude once. Turned out to be a combination of too much idle air bypass and a maladjusted throttle position sensor. What it was doing what reaching 1300rpm or so (minimum speed for throttle closed fuel cut), seeing zero throttle and cutting the fuel. Sound similar?

[worldwalker]

Yeah just finished a full bleed and replaced a few hoses and its still there. I was just about to post that I'd narrowed it down the the air bypass valve.

With the idle screw all the way in it still runs but at about 500RPM. I've removed the hose that runs from the bypass valve to the idle up control? (I believe thats the valve) and there is a lot of vacuum then the engine stalls. The hunting continues with the bypass valve end of the line blocked; although I cant determine how this line ties into the system as I thought the bypass openings was within the TB not from an external line. The only thing that seems to have stopped it is screwing the idle screw all the way in. The lower the RPM the better it seems, the further out the idle bypass the the larger the oscillation in RPM and the more rapid.

I'll test the TPS now and readjust the TPS.

Thanks. Nick

[worldwalker]

After all that the air bypass is now leaking coolant so its had to come out. I thought I might as well bench test the valve but even using boiling water wont close the valve. It doesn't seem to move anywhere. The odd part about this is that the car still has a high idle while its cold and lowers as per normal which leads me to believe its still functioning fine despite remaining open once warmed. At this stage I'm thinking of blanking it off and returning the water lines but I don't to do this and bleed the system again if its not a fix.

The other problem I found was that the fuel cut and return RPM with the TPS disconnected is way to low (900return, 1200 cut instead of 1200/1600).

The engines cold start circuit is stuffed as well but as I said its only to get it on the road then the engines gone. If blanking the bypass will help and the car will still run despite no cold start circuit I guess that will be the option.

Thanks.

Nick

[BLSTIC]

Ok so you have established that the tps has *some* effect. Is it adjustable on your engine? If so mark where it is now and rotate it against the throttle opening (i.e. "advance" it, to make the ecu think the throttle is open further than it is) while it's hunting. That stopped ours hunting but the idle was still high.

Our honda had two idle speed controllers. One pwm (ecu controlled) item that corrected for load and another that used a plunger controlled by water temp. This plunger sat in an adjustable seat. If yours is like that you can do what we did and simply close the adjustment rather than make blanking plates.

[BLSTIC]

I should mention that since then we have blanked off BOTH idle speed controllers (it's in a race car) and set the idle for about 1000 rpm hot and except for the first 10 seconds of cold start running it works fine. But we didn't have any varying loads.

[worldwalker]

I retested the bypass valve and it was working but very slowly and not closing completely, I'm assuming this was the problem. It's taken a lot longer than I would rather but I've managed to blank off the air bypass valve and left the computer one attached. I readjusted the TPS to be within factory specs, unfortunately I can't adjust it on car but its significantly different to where it was. Fingers crossed this resolves the issues.