MFI - Can't set idle

[edmayo]

Can I assume you really did have the hot air hoses on the thermostat,,,and just removed them for the picture?

[chris belyea]

Yes, I removed the hose for the purpose of the picture

Chris

[2.5MFI]

Ed,

Isn't the idle stop screw the screw on the pump.

To help clear this up, and thanks to Jeff for pointing this out, this set screw/w nut is a Porsche MFI tool believe it or not. Forgot the tool # but this tool was in the dealership service dept. and used to set part load adjustments with CO readings. After the the service the tech would remove the tool (set screw/nut) and put it back in there tool box. No MFI pumps were delivered with this screw/nut installed. This was only found on the 1970 pumps.

[chris belyea]

Thanks for clarify the idle stop.

So could the idle mixture adjustment be likened to the changing the size of the idle jets on a carburetor?


Chris

[2.5MFI]

Chris, The idle adjustment screw on the MFI pump changes the fuel mixture for the area between 600 engine RPM to about 1450 engine RPM. So yes, it's like changing the idle fuel jets in a carb.

[taldora_2008]

Hi Chris, have you checked that the linkages (and throttle butterflies) are returning back to closed after it warms up? I forgot to install the circlip and shim on my reverse lever assembly, when I first reassembled mine, and it led to some erratic idling.

[chris belyea]

So I've spent the last several weekends going through everything to solve my idle problem. I went back and checked the ignition timing. I found that at 950 RPMs, I have 10 degrees of advance. At, 6000 RPMs I'm right were I need to be, 30 degrees. From what I see in the manual, at 950 RPM, I should be about 0 degrees. So from what I can tell, my distributor is only giving me about 20 degrees of advance. The distributor is not original to the car and is new for this rebuild. The distributor is correct for a 1970 911E (0 231 159 006 (JFDR6)). So my question is can the the distributor be causing the problem with the idle and why I have such a hard time getting lower once the car is warmed up? Currently, once the car is warmed up, the car idles at 1600.

Thanks

Chris

[edmayo]

As an experiment set idle timing to between 0 and 5 degrees and don't worry about the 6000 setting. See if that helps your idle speed. Have you turned down the air by-pass screws? While engine is idling pop off each linkage rod one at a time and see if idle speed changes. There may be a rod too long.

[chris belyea]

I'll have to try adjusting the timing down and see. Yes I adjusted the air by-pass screws and there aren't enough turns in them to bring it down enough. I checked the linkages and they are good. I popped all of them off and no change in idle. I then connected one at a time and again no rise in idle. Logic would seem to dictate that if I lower the advance, the RPMs should come down. Right now the only way I can get them low enough is to lean the main rack out.

Chris

[edmayo]

Unfortunately leaning the mixture is not the way to set idle speed. You may need to have the throttle bodies rebuilt, air leaks there are a common problem particularly on 69-71 throttle bodies.