Ford focus idle problem

A week or so back I posted that I had a problem with a ford focus Mk1, 1.6 petrol, 2001 where the idle would sit at 800rpm and then every two
seconds would blip to 900 or 1000 rpm. I reported that a can of throttle body cleaner had cured it. Car has done around 140,000 miles.
Alas a few days later it started blipping again so I decided this time to remove the idle control valve to thoroughly clean it, again with throttle body cleaner.
I now have a worse problem. When putting the car in neutral the revs will stay at 2000rpm before falling back to around 900 rpm after around 2 seconds. Also on start up the rev will jump to 2000 rpm before falling back to a more normal idle speed a few seconds later. Revving the engine and then releasing the throttle results in the revs dropping to 2000 rpm before falling to 900 rpm after 2 seconds.
I notice no drop off in performance when driving.
Any suggestions?
Things already checked: No apparent air leaks. Hose behind manifold that often fails was replaced less than a year ago. Gasket on throttle valve looks ok and I have carefully re-seated the valve a couple of times. Disconnected the throttle valve electrical cable - car still starts at 2000rpm and after 2 seconds falls back to 'near' normal idle revs. I'm assuming that the default position of the valve is closed as springs shut with no electrical connection. Replaced the throttle position sensor (just in case). The throttle is not sticking and the throttle butterfly fully closes immediately when the throttle is released.
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alan_m wrote:

No obvious answer from me, I'm afraid. But I had one of those come off at one end soon after one of the connectors had been replaced. But it made my idle permanently high, not up and down. Might be worth checking it's not flapping about at one end like mine ended up doing.
I think they say you're not supposed to clean the throttle body yourself (because they're coated with something), but I did it with carb cleaner once, and it didn't seem to break anything.

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On 15/02/2018 15:51, alan_m wrote:

faulty idle air control valve, cleaning it might improve things, but it will inevitably recur, new ones are not very expensive.
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On 18/02/2018 13:59, MrCheerful wrote:

I already have a new one on order but am not 100% convinced this is the problem unless it is not shutting off.
Removing the power/control to the idle air control valve and the idle still runs fast. The valve appears to be spring loaded and it should be fully closed without power/control.
My car has limited OBD diagnostics but using a USB/OBD interface and Forscan software I can see during the fast idle that the MAP (no MAF on this car) outputs around 1V which is I believe about correct for an idle (and it does respond to acceleration). I can see that the ECU wants to set around 800rpm and I can see the idle control trying to set a low air flow - but not getting there. I can also see the idle control signal matching changes in the MAP outputs on releasing the accelerator.
I have checked to hoses etc. for leaks and all look OK I've checked the PCV and it appears to be clean and working.
I've also disconnected the battery overnight to reset the ECU and then gone for a 10 mile drive after on starting the engine for the first time leaving it idling for 15 minutes. If anything the problem (2000 rpm falling to 1000rpm when selecting neutral and car is motionless) is worse when the engine is hot. The temperature sensor is working as reported on a Forscan trace.
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On 18/02/2018 15:22, alan_m wrote:

Postman delivered a new Idle control valve this morning (Ebay £25) and I fitted it in 10 minutes - in the pouring rain :( The battery was disconnected overnight to reset the ECU and I have driven 30 miles so that the ECU can re-learn my driving habits. The new idle control valve has almost fixed the problems I was seeing, now 1200 rpm falling to 800 rpm after 2 seconds when selecting neutral and car is motionless. The ForScan[1] OBD traces show the IAC control making only small corrections rather the more erratic higher magnitude corrections with the old valve.
I'm not sure all the problems with the idle have been sorted but I can live with them for now as I'll be changing the car in the next month or so.
Note the fast idle problem only started after I had removed the idle control valve and squirted in some throttle body cleaner (it wasn't labelled as carb cleaner). The old gasket is still in use with the new valve as the new gasket that came in the packet was a different size from the fitting grooves in the housing.
[1] FORScan is a (free) software scanner for Ford, Mazda, Lincoln and Mercury vehicles, designed to work over ELM327 and J2534 Pass-Thru (OBD) compatible adapters. My adapter was under £10 from Ebay.
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On 19/02/2018 12:45, alan_m wrote:

the idle should pause at 1200 and drop to 800
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On 15/02/2018 15:51, alan_m wrote:

check the breather pipe under the manifold at the front of the engine, any breaks in this can cause serious problems.
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