I think that I may be on the verge of discovering why the engine continues to surge even after thoroughly cleaning the ICV
( a number of posts mention this )
A conversation with the owner of the place that did my air con. conversion started me thinking; he said that they get the same problem on Subaru's and it's the MAF sensor that needs cleaning !
I'm pretty sure that Subaru use a hot wire or film sensor, so I was puzzled how this could apply to the flap operated system in the Carlton.
If you think about it, the original fault is caused by the ICV sticking due to crankcase oil residue and cleaning it radically reduces the problem but later I found that to a lesser extent it crept back and no amount of cleaning or replacing of the ICV did any good
The symptoms are exactly the same, so it's likely to have a similar cause and the flap operated airflow sensor is in the same air circuit.
Removing mine and stripping off the plastic cowl that holds it to the filter housing made it possible to get a finger inside to operate the flap.
I found that with the flap closed it obviously abutted a stop somewhere and there was the smallest bit of 'sticktion' when moving it off the stop
A small inspection mirror and light enabled me to see that the stop was on the engine side of the sensor housing and is a flat toothed slightly flexible compound insert which the damper flap rests on with the flap in the closed condition.
The contact with the stop is causing the flap to stick to it slightly, due either to a small amount of crankcase oil residue ( most likely ) or the compound is degrading and getting sticky ( I bloody well hope not
)
The scenario is : - The ICV is commanded to open a little more by the ECU, but when it does there is no increase in airflow due to the AFM flap not being free to move so it is commanded to open even more and that is enough to unstick the flap in the AFM.
The flap pops off the stop, but there is now too much air so the ICV is commanded to close and the AFM drops back onto the stop and sticks again
If the sticking is bad enough the whole process can run out of control until the engine stalls, the same as when the ICV is sticking !
I'm trying to work out the best way of cleaning the residue off this stop, because it is only visible with a small inspection mirror; I reckon that a small piece of petrol soaked rag on the end of a bent wire is the solution ?
Edit : - Just finished cleaning it, there was what looked like a varnish (Probably oil based) on the part of the flap damper abutting the stop.
I reckon that when the engine got the under bonnet temperatures high enough, this got pretty sticky !
I found that the best way of cleaning it was using a small squirty bottle with petrol and putting enough petrol in with the AFM turned on its edge so that a small bath of petrol was formed then working the flap to and fro in this.
There is now no sign of this 'varnish' and no sign of 'sticktion'
Time will tell whether this is the cure, or whether everything I've said is utter b*****ks and it's something else entirely
End of edit.
If you do strip off the plastic cowl, make absolutely sure that when you put it back together you use threadlock on the bolts inside it, because if they subsequently work loose and get sucked into the manifold intake you can say goodbye to your engine
For 12 months or so my Diplomat engine speed has occasionally 'surged' slightly at tickover, this only rarely happened under a specific set of circumstances ie, engine hot, allowed to cool somewhat ( park at supermarket, shop then come out and restart )
when you put your foot down even a little to move off, it came out of that mode and did not return to it.
However it recently started to surge and then stall, this is much more annoying, so time to do something about it.
Reviewing the comments on this forum about this sort of behavior it all pointed to the idle air control valve ( ICV or sometimes IAV )
On the 2.6 engine this valve is hidden under the inlet manifold on the nearside and is all but invisible ! there is a ribbed pipe with a sharp 'u' bend leading from it to the rear of the inlet manifold retained with a hose clip, unscrew the clip and with a wide bladed screwdriver, ease the hose off the manifold.
The other hose is a smooth one with numerous bends and is push fitted to the underneath of the inlet manifold in front of the accelerator linkage, ease it off.
The valve is push fitted into a large rubber sleeve fixed to the inlet manifold, gently ease it out because on the end of the valve inside the sleeve is the electrical connector, there is not much free cable to play with and ripping the connectors off the plug would indubitably cause mutters of 'oh dear' 'tut' or even 'bother'.
I found that unplugging the valve to be the worst part of the job, finger and thumb pressure on the retaining clip is supposed to enable its removal !!!
Remove the hoses and use your chosen cleaning fluid ( Carb cleaner etc. ) I dumped mine in a pint of petrol and went for a cup of tea !
After soaking for a while, give it a good sloshing round then leave it to drain.
Looking inside the hose connector at 90 degrees to the valve body, you will see what looks like a silvery segment of a cylinder, don't poke or risk scoring it, look in the other connector and you should be able to see where to push a 3 or 4 mm wide screwdriver blade down to rotate the valve.
keep pouring some very thin oil onto the silvery cylinder segment and rotating and wiping that surface until the oil no longer gets stained black.
Clean the hoses also before re-assembly.
My car has only done about 80,000 and the crankcase oil residue in the inlet manifold and ICV was minute, but still enough to intermittently jam the ICV; an engine with more wear and consequently more piston blow by is likely to jam this valve fairly regularly, a new valve is about £125 I believe !!
The Bosch part number is 0 280 140 516 with the number 011 circled below this number.
It is a 2 wire rotary solenoid with an internal spring return operated by a variable pulse width signal, almost certainly from the engine control unit.
My engine is now perfectly behaved !
