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[T3] Idles on 2; runs on 4 (Update/recap/ SOLUTION!)

Here's the recap of my problem and a few tests that were run to try and solve 
And like any good puzzle or riddle, the solution is at the bottom.

>> She's a 1973 FI MT Squareback.
>> I ran the tune up; it consisted of an oil change, valve adjustment, plugs, 
>> points and condenser, adjust timing, check idle. This was not my first 
tune up. 
>> Everything was great for a little more than a week and then she began to 
>> rough. At first, she just wanted her accelerator pedal feathered at the 
>> to keep the RPMs up. A little later, she wanted the pedal tickled to keep 
>> stalling. Eventually she would stall and I'd have to crank her over and 
>> until she'd catch, blow petrol-smelling smoke, then continue.
>> Since I'm an avid reader of the type 3 list, I knew immediately that if 
>> car runs rich it must be a problem with the Voltage Regulator or the Cold 
>> Valve. I ruled out the CSV because I live in Southern California and the 
>> problem doesn't happen until after the car has been started.
>> So I connected my trusty VOM to the battery and got 12V. As the car 
>> approached medium RPMs, the VOM began to read higher and higher and 
leveled off >>just shy of 14V. But that's what it's supposed to read! The Voltage 
Regulator is not 
>> my problem.
>Make sure that the CSV wiring between the CSV and the temp switch has 
>not gotten shorted to ground. This can mimic cold weather. The best 
>way to eliminate the CSV as part of the problem would be to just 
>unplug it temporarily, as a test.

Yes, as a test, the CSV was unplugged. No change.

>It's possible that your VR only goes bad as it warms up, so try to 
>take the car for a drive and then check the voltage after the drive.

A new VR was tested but the problem continued.

>> He (my mechanic) tested a known-to-be-good Pressure Sensor and nothing 
changed. >> He cleaned the trigger points and nothing changed. He retested for 
spark -- it's fine all 
>> around.
>Is there any chance that the PS on this car is the wrong one. The one 
>for 70-1 has a couple of vent holes in the "cover" and these indicate 
>a style of PS which has a brass diaphram which can crack and leak. 
>The 72-3 PS came with a black cap over the adjustment screw, but 
>sometimes these have been broken off to tamper with that screw. You 
>really want one which hasn't been tampered with.

The PS is the right one. It's an "E" PS with an unmolested black cap.

>>Check the dwell and timing with a dwell meter and timing light?

Dwell and timing checked with meter and light. Timing is set to 5d before TDC 
-- the third mark from the left (she's a 73) per Bentley. Dwell fluctuates 
ever so slightly. I think the bushing around the shaft is beginning to show its 
age. But that shouldn't cause my problem.

>> But he discovered that the injectors for 1 and 3 were spraying too much 
fuel on 
>> each impulse. This is particularly troubling because the paired injectors 
>> 1&4 and 2&3. The injector wires were reversed on each side and 2 and 4 
>> started shooting too much fuel while 1 and 3 were fine. This tells me that 
it's not 
>> a problem with the injectors themselves.
>Yes, sounds weird. How did you tell this? It's hard to see this 
>visually, did he actually measure it? If this is true, I agree that 
>it sounds like a brain problem, but such problems are actually 
>exceedingly rare. Were these injectors all genuine Bosch?

The injectors are all Bosch 007 yellow injectors. The test was done by 
allowing the injectors to spray into a jar. Same thing was done after reversing the 

>> Next, he called to ask if I had another ECU we could try. The short answer 
>> no. She's a 73 with an "E" system (brain, pressure sensor and throttle 
>> switch all match). The only ECUs I have are a "D" and a blank. There is no 
>> part number anywhere on the blank. So we tried them both.
>> The "D" brain didn't seem to affect anything. The blank, however, was 
>> story altogether. Instead of pushing out too much fuel, this brain allows 
>> fuel to 1 and 3 while she idles. But when she gets a little gas, she'll 
>> fine on all four.
>> Personally, I don't think the problem lies within the ECU. But I'm open 
>> minded enough to consider it as a possibility. I have a spare "E" ECU on 
the way 
>> but it won't arrive until some time next week. Anybody have any ideas?
>I also have E brains here.

Thanks, Jim. I have an "E" brain on the way. I'll let you know if the one I 
get doesn't work.

>I assume you checked the hose between the intake air distributor and 
>the pressure sensor, just to make sure it hadn't fallen off.

Yes, checking that hose for a leak was one of the first things I did before 
taking it to the shop.


If you read closely, you saw where the dwell was fluctuating. After 
accumulating three more black sticker "E" brains (none of which solved the problem) and 
testing known, good spares at literally EVERY point in the FI system. The 
problem was solved by testing another distributor. I don't know if it was an 
electrical issue inside the distributor or not. The best I can wrap my brain 
around is the worn bushings allowed the dizzy to spin out of round at idle, and 
then spin true at speed. The bottom line is that the distributor was the problem.

Jim, are you still rebuilding distributors? May I send you two that I have? 
One would be the "problem child" described above and the other would be one I 
picked up a few months ago -- condition unknown. Both are 311 905 205L.

List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org

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