A/C and idle control

fizban · May 03, 2012, 11:00:48 PM

Hello,
Another issue i have is that when i turn my A/C on, my idle drops from 1050 to 900.
With 900 rpm idle, when i flip the throttle or release the paddle, rpm goes to 300-500 and sometimes the engine stalls.
No matter what i do, the A/C keeps bringing down the idle RPM.
Any idea how to over come this? Do you need any conf files to review, maybe?
Thanks,

JohnP · May 04, 2012, 06:40:57 AM

I would like to know this solution as well. My 1.8t 20v swap does the same thing..

My only added info that helped me, was adding 2*-4* ignition timing over standard idle rpm in lower rpms 500,800. That helped the lower rpm idle recover quickly and nearly eliminated stalling with the a/c on. It still happens once in a while when really hot out side. 100*F

fizban · May 04, 2012, 08:58:40 AM

Good to know i am not the only one with this problem. I also use advance in the lowe RPM to avoid stalling. at 500 RPM i have 18 deg and on 1000 RPM i have 12.
The thing is that my OEM ECU actually brings up the idle once the AC is on, while the VEMS is bringing it down.
So there are 2 option:
1. I didnt tune IAC well enough. My idle RPM is set to 950, but its actually 1050, until i turn on the A/C and it drops to 900.
2. VEMS is not dealing with AC compensation , it was simply designed for cars without A/C (?)

GintsK · May 04, 2012, 01:45:14 PM

It is easy to maintain idle when a/c engages with switchable config.
Or do you use it for other purpose??

fizban · May 04, 2012, 02:30:22 PM

How can i switch config when A/C engages?

mattias · May 04, 2012, 05:04:08 PM

This is not a big problem to me, at least not with a properly setup IAC valve and idle ignition advance control enabled.
The ignition takes care of quick changes, the valve catches up for the larger changes.

Many people use too much idle ignition advance to begin with, 5-10 degrees at most on modern DOHC engines. Then let idle ignition advance control raise that by 5-10 degrees further to avoid stall and quick recovery. The IAC valve reference curve should be significantly higher than the target rpm, the regulator takes care to close the valve only to bring rpm down. Set "IAC integral under lowmap" to 0 and you get better recovery from slight throttle movements, as the IAC valve will go to ref curve value and then gets regulated down.
This stuff works better with many trigger teeth (36-1, 60-2, etc..) as only one tooth per cylinder is not enough at idle to get good help from the idle ignition advance control, the speed of the engine changes too much between teeth.

Of course, this could be solved even better if "idle rpm target" was added to the anytrim functions, and let the "A/C on" switch activate a free analog input.

GintsK · May 05, 2012, 10:04:48 AM

Quote from: fizban on May 04, 2012, 02:30:22 PM
How can i switch config when A/C engages?

You need to connect either 0V-5V or 0V-floating signal to one of analog inputs. (do not use 12V signal!!! - use relay then to invert it)

Config switch is easy - just configure input channel at Configswitch (you can review it under RAW ADC window [just hit Backspace]). Open your current config in offline mode, rise IAC reference curve by couple percent, save it; and then go to config upload advanced and upload new config to B only. That's it.
I think it should work faster than target rpm change from analogue input.

Gints

MWfire · May 05, 2012, 10:45:13 AM

for weak engines i use config switch with more ref_DC for idle.
For strongest, ign advance control + big D(150-250) in PID control.

fizban · May 06, 2012, 09:44:21 AM

Thanks for the answer, guys, but the vems was PNP. You lost me in the 0-5v to analog input.
Which analog input? ???

GintsK · May 06, 2012, 10:23:09 AM

Heave you some paper with it? You have some analog inputs in 6pin connector.

fizban · May 06, 2012, 11:00:27 AM

No papers, but i will consult DP engineering (they made the ECU)

Also - my PW in idle is 2.1ms. When i turn the A/C, it goes to 2.7ms even though the RPM drops to 900. VE table values are almost the same (if not lower) at this level.
Is this expectable (because of the extra load of the A/C)?

GintsK · May 06, 2012, 06:03:05 PM

Expectable. At higher MAP reading but same VE value final PW will be higher.

fizban · May 07, 2012, 02:37:17 PM

Thanks. I will try to consult DP-Engineering about analog inputs. :)

AVP · June 05, 2012, 10:41:21 AM

im with Mattias on this one.

i have tested 2 audi RS2 with A/C and idle settings according to his guidance and the idle drop when A/C works is minimal and valve/timing is very quick to control it.

No need for configswitch for such an issue anymore.

Joof · June 06, 2012, 11:55:32 PM

I just wanted to post a +1 to MWFire, having a big D for the pid control helps immensely.

At least on a bosch 3-wire IAC...sans a/c I had a very low value that worked well but once the heat hit and the a/c was on I had a nice stumble....raising the D upwards of 200 worked wonders.

So thanks for sharing ;D

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A/C and idle control