Dose out Motronic ECU adjust for a/c compressor running
 

Hi guys,
On my old 928 there is a solenoid that opens to increase engine speed slightly when a/c is on. Later 928's had that incorporated in there ECU's
Does the 911 Motronic have a control over the idle air control valve to increase engine speed in a similar way?
On my car I can tell at idle when my a/c kicks in. The idle drops 100 rpm or so, then levels off again.
Thanks,
Dave

I recall its in the DME schematic, the fella to answer this is "Sal".

The 84-89 DMEs do have this ability built into them. However, the factory idle speed with and without the AC is set the same at 880RPMs but for the 84 DME it's set at 800RPMs. If you have the very early 84-85 DME your base idle is 800RPMs and this is way to low! It gets even worse if you turn the AC on. The other thing built into the ICV code is the ability to anticipate the need to further open the ICV an extra 7% when the AC comes on but this is only to help get you back at the target of 800 (early cars) or 880 (later cars)

Now the good news: The very best solution for any early DME is to convert it to the 1989 28pin chip as it has the 880RPM idle plus it also has better ignition maps than the 84 factory chip. Just the ignition maps alone are worth 10HP over the 84 chip. Then better yet I can also change the stock 89 chip slightly to idle at 880RPMs without AC on and 960RPMs with it on. I can easily help you remedy this problem if you like. I will also help provide better return to idle control so that the engine goes back to idle speed slightly slower than the stock setup. I have full understanding of the entire DME program including how the DME uses the ICV valve to control idle.

I only work with 28 pin 89 chips so the first order of business is to update the 24 pin DME to 28 pin 1989 spec. Then once this is done I can address the idle RPMs to whatever you like with AC on and AC off, I recommend 880-920RPM with it off and 960-1000RPM with it on.

PM me if you would like help and changes.

Kuehl, thanks for the recommendation.

Thanks, Sal,
I think I will add this to my list of winter projects for next year. I have a Steve Wong chip that came with the car. I assume I would need to send you my ECU.
Dave

Actually, the 911 ('84-'89) does not have an input which indicates that the compressor
is on as does the later 964/993 Porsches. So the DME ECM only detects the additional
engine load via an idle drop which results in an idle compensation.

Dave,

The 84-89 cars do have the AC signal feed to the DME on pin #29 it's right in the schematic. And the code in the DME looks at this input and opens the ICV valve an extra 7%, but it does not increase the idle speed although it has provision to do so. I know this 100% because I know how the code that controls the ICV works.

Just want to be sure folks get the correct information.

Dme
 

+1