Hello all!

Prior to putting my 964 into storage for the winter, I had it dyno'd. Immediately after the dyno run, the check engine light came on and stayed on. Well, I was able to troubleshoot using the blinking light technique (thanks Bill Wagner!), and found code 1115 (idle speed contact break).

Well, now that it is almost spring, I have decided to troubleshoot the problem. Thanks to Adrian's book (p. 390), I was able to use the throttle valve switch connector to measure resistance across the switch. When the throttle is at idle, resistance across pins 1 and 2 is about 0 (<10 ohms, which is good). The full load or throttle wide open switch, measured at pins 2 and 3 of the same connector), measures open. Also good.

When I have the throttle depressed to WOT, pins 1 and 2 measure open (good). However, when I measure between pins 2 and 3, I also measure open (not good, should be < 10 ohms).

Now looking at the book, I see that there is no fault for a full load contact break. So when I start the car, I should have no check engine light or faults. Which is what occurred.

However, I am now suspecting my "microswitch for full load contact", according to the manual, since it did not close on WOT.

I am still suspecting the idle speed microswitch, as it may be failing intermittently. Does anyone know the history with this part failing? Is it typically the switch or a loose connection? Mine appears to be a loose connection, since the 1/2 dozen times I tried it, operation appeared fine. But I will continue to watch it.

Now that the "microswitch for full load contact" does not appear to be operating, does anyone know of any adverse affects of driving the car until I can replace it? I suspect that the control unit will not switch into open loop mode, and I will not see maximum performance out of the car.

Before purchasing the car (2 yrs ago), the mechanic who did the PPI told me that the throttle was adjusted back, so that flooring the pedal would not allow WOT. This was suppossedly adjusted back to normal prior to the purchase. When I had my service done at a dealership, they did not notice anything. Not that they looked, but they seemed quite thorough. Since I was performing my measurements by keeping the pedal floored, I am wondering if my throttle needs adjusted. I suspect that the next measurements should be done by manually moving the throttle on the engine, not the pedal.

Thanks in advance,

Ron

91 C2 Cabriolet
85.5 944 NA

 

Ok. I did more troubleshooting, and sure enough, when the gas pedal is floored, the throttle does not move far enough to actuate the throttle wide open switch. When I manually actuate the switch, pins 1 and 3 short, not pins 3 and 2 as stated in Adrian's book.

So that leaves a few questions:

1. Is my throttle wide open switch bad? Am I troubleshooting incorrectly?

2. How does one go about adjusting the throttle? I am showing my ignorance here.

Thanks,

Ron

91 C2 Cabriolet
85.5 944 NA

 

You've proved that the switch closes properly by manually closing it,
versus being actuated via the throttle linkage. This can lead to an
intermittent operation as you fully depress the throttle pedal.

Therefore, try to adjust the switch (There should be a locking set screw.),
so that the switch closes before WOT is fully reached without affecting
the idle switch setting.

Good Luck
Loren
'88 3.2

 

Hi Ron,

I have a strong recollection that the centre pin (1) is earth, and you need to check resistance between pins 1 and 2 (idle) then pins 1 and 3 (WOT).
I could be wrong - my car's in shipping so I can't check. apologies in advance if I am.

Secondly, for some reason the WOT switch is often positioned where it won't engage on full throttle (no idea why - mine was). The switch can be repositioned so that its cam follower engages the switch earlier, but take care with the two fixing screws, they are quite fragile and easily burred.

Good luck

Ade