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Discussion Starter · #1 ·
What makes the idle speed change when the AC is turned on (under load) i.e. is the engine timing changed by the ECU e.g. 7 degrees to 20 degrees or is an extra air valve opened up AC under load (like in some cars)? Anyone know?
 

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I think I used to have an ICV, or was that an MPV, or possibly RTV? I absolutely know I have an ECU & have recently established mine also has an AFM, I'll be ****ed off if you lot have an ICV and I don't, so I'm off to check.

P.S. - What colour are they?

Aitch
 

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Discussion Starter · #5 ·
The ICV opens a little more.
Thanks Andy. I think (again) that my idle speed problem is because of the ICV but I replaced it before to no effect. I was wondering if it was the input that controls the ICV that is at fault as when the idle problem starts it can be stopped by switching the AC off or on - very strange. Robbie got around the problem a good bit by mapping the PFC to make the idle only jump up and down by 100rpm instead of the usual 600rpm but it is still there and it is pi$$ing me off again.
 

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Discussion Starter · #6 ·
I think I used to have an ICV, or was that an MPV, or possibly RTV? I absolutely know I have an ECU & have recently established mine also has an AFM, I'll be ****ed off if you lot have an ICV and I don't, so I'm off to check.

P.S. - What colour are they?

Aitch
Working in IT my life is one big TLA!
 

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Have a look in the workshop manual @ the section relating to checking the ICV and see if you have a wiring fault or something else.
 

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I assume you`ve also followed the idle learning procedure for PFC? This needs doing again if you`ve changed ANYTHING relating to idle air flow - e.g tweaked the air by-pass screw or changed / moved the ISCV.

This also assumes a good base fuel map at/around idle.

The AC high pressure switch controls the opening of the ISCV ahead of the AC clutch coming in. Check on the PFC SW screen that the switch is errm switching......
 

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Discussion Starter · #9 ·
The PFC seems to flag the AC switch handy enough.

I got the car mapped by Robbie (TDP) so I reckon Robbie would have run through the learning process for the car as per usual.

I had tried the learning process in the pass myself (30 minutes or so) but it seemed to steady itself a bit after 20 minutes but never really settled no matter how long you left it for.

Something has gone "off" so to speak as the idle slowly went off on a mad one over the space of 3 weeks (about 6 months back) without any mods or changes whatsoever being done to the car. It has just been a bit of a head scratcher trying to find out what went wrong and I have changed LOTS of bits and tried all the recommended things with no joy.

It's no problem driving it but just one of those little problems that fcuks you off - Robbie thought it my be the butterflys not balanced correctly at idle which could also explain why switching the AC off/on/off can settle them but who knows?
 

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To perform the learning procedure:

Get car hot.
Save your good map to PC.
reset PFC
download good map.
Start car with no consumers, run for 5mins
Switch full electrical loads, run for 5mins
Switch elec off, switch AC on, run for 5mins.

O2 feedback on or off on your car?
 

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Discussion Starter · #11 ·
I have the PFC manual etc but it does not mention resetting the maps before doing the learning. I can go through the learning process again although it didn't help before.

The car can idle perfectly well for ages but then usually after a spirited run it begins to act the [email protected] It also happens when the clutch is depressed leading me to think I may now know the culprit.

I know from the manuals and wiring diagrams that the AAC signal comes off pin 4 and is affected by neutral and a/c signal so I now reckon it is the AAC that is faulty and not the ICV that is the issue.

Anyone know where exactly the AAC valve is - I was once told it was under the main engine components - the picture in the manual is crap.
 

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The point with `reflashing` the maps is that any learning that is done on a dodgy fuel map effectivey means the PFC is attempting to compensate for both a load change at idle and potenital AFR variance. AFR variance changes the torque output which affects the load rejection capability. OEM ecus` have PID based idle speed control algoriths with clips on both the amount of spark advance / retard and ISCV duty cycle +/-. Over time the clips are allowed to be modified by the historical running conditions. No idea how clever the PFC software is in this regard. When you reset the PFC you are effectively clearing any learnt bandwidth to allow it to home-in on the `correct` values......
 

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Discussion Starter · #13 ·
When I replaced it with the standard ECU it did the same thing so I reckon it's not the learning mode that is the issue but a knackered part somewhere which is looking very like the AAC valve at the moment.
 

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That's it, i'm off to follow another thread, you prats are doing it deliberate now, in the next life may you be named with an abreviation!

Aitch
 

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Discussion Starter · #15 · (Edited)
LOL (the irony of it all)

Quick Update: Not AAC valve as Robbie checked it so looking more like the front O2S again (Oxygen sensor for Aitch lol).
 
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