idle control behaviour

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johnfelstead
Posts: 23
Joined: Wed Jan 29, 2014 12:23 am

idle control behaviour

Post by johnfelstead »

With the weather being very hot recently, i thought i would have a play with improving the idle control to compensate for having the Air Con switched on and higher than normal ACT which affects idle stability.

I had no idle duty added for when the Air Con is switched on and no ACT based idle duty added. So i added some duty for these to see what effect it would have. This improved the high temperature behaviour for idle.

Having now logged the Throttle Bypass Valve duty and the various idle parameters, its not doing what i expected.

When driving at normal speeds the TBV duty is not sat at the bypass duty in run mode value (5%), it follows the open loop idle control settings, so if i have 5% more duty added for AC switched on and 2% added for ACT higher points for example, the TBV duty sits 7% above the base duty value set in the open loop control.

So without any compensations for Air Con and ACT, whilst driving normally at speed the TBV duty is sat at open loop value of 40%, then add any corrections and you would see 47% in the above example.

Why is this, what is the purpose of the Bypass Duty In Run Mode parameter?

If the TBV duty is varying with compensations, this is going to have an effect on the amount of air being passed through the throttle body, so the load reference of TPS isn't going to be valid or consistent, it's going to vary depending on if the AC is on or off if you are using any ACT compensations for the idle control that will also alter the amount of air flowing compared to your load reference. This can't be a good thing?

Any thoughts on this?
Andy.F
Posts: 3
Joined: Sat Apr 14, 2012 10:55 am

Re: idle control behaviour

Post by Andy.F »

John, your load reference is map1 not tps or iscv position. So the change in idle valve position is seen as a shift in map value. Unless that's not what you were meaning?
Hugh
Posts: 49
Joined: Thu May 19, 2016 7:54 pm

Re: idle control behaviour

Post by Hugh »

John,

You don't say which idle control - bypass or DBW that you are using.

On my twin DBW set-up, I have no additional duty from 20 C

Air Con is an additional 4% duty.

I have seen problems with the DBW1Duty compared to DBW2Duty where the throttle stop was not accurately set, so was trying to close one of the throttles on to a throttle stop.

I also found an old carburetor balancer to be invaluable when balancing the flow between different banks.

If you have not already done it, I found that calibrating the DBW throttle position sensors allowed the rest of the parameters to behave in a predictable way.
johnfelstead
Posts: 23
Joined: Wed Jan 29, 2014 12:23 am

Re: idle control behaviour

Post by johnfelstead »

Andy.F wrote:John, your load reference is map1 not tps or iscv position. So the change in idle valve position is seen as a shift in map value. Unless that's not what you were meaning?
Good point Andy.

Would having a more cracked open idle control valve not have some impact though? It's similar to installing a larger throttle body as more air is flowing than when you maped it, for the same throttle opening angle.

Also, it appears the Bypass Duty In Run Mode parameter doesn't do anything, the Idle bypass is set by the base table used during warmup. If you have a throttle blip active that does override the main bypass table value, but it never seems to drop to the Bypass Duty In Run Mode value.
johnfelstead
Posts: 23
Joined: Wed Jan 29, 2014 12:23 am

Re: idle control behaviour

Post by johnfelstead »

Hugh wrote:John,

You don't say which idle control - bypass or DBW that you are using.
Thanks for the reply. It's the stock idle control valve on a drive by cable MY05 Subaru, which is just an air bypass.
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