WUR Hypothetical Question

[Mac-Porsche]

Been looking everywhere for an answer to this question, can't seem to find it...

Hypothetically... If you were to disconnect your WUR, assuming everything else is working well in the CIS system, what kind of behavior would you expect?


Here's why I'm asking... I have a 1981 911sc, (-090 WUR), with very recent full rebuild.
My car has been having issues with rough cold starts (takes 5 - 10 seconds to start cold, and slowly, begrudgingly, stumbles and starts). Then the first 5-10 minutes of driving, the acceleration feels suppressed and/or sluggish. Once warm, car starts and drives great. I've posted about this a few times before, with similar comments/suggestions:
- Check fuel pressures - All checked within spec.
- Check fuel mixture - Running at ~13.1 afr, ~3.1 CO (from Gunson), with O2 unplugged.
- Try different WUR - Borrowed a spare from an '83 911sc (also -090), same behavior.
- Check WUR resistance - Measures 26 ohms below ~65°F, at 78°F [temp in my garage where I keep the car] it measures 10.2 ohms. I think this is because of the later-style WUR "2-stage" heating element.

Frustrated... I've noticed something peculiar recently...

Week ago, I forgot to reconnect WUR after checking resistances. Started the car cold next day without WUR - started great. Then drove really good cold. Lots of pep!
However, once warm, idle began to drastically swing and then engine stalled repeatedly. Realized WUR was unplugged - plugged back in WUR. All good.

Didn't think much of it, but then made the same mistake yesterday. Started car cold with WUR unplugged. Car started great, ran awesomely. Then once warm, huge swings in idle, engine stalled. Again, noticed unplugged WUR, plugged WUR back in, all good.

So... My conclusion...
WUR unplugged = runs good cold, stalls warm
WUR plugged in = runs bad cold, good driving warm

Hence my hypothetical question...

[RarlyL8]

On the surface this is textbook worn out WUR. You say all fuel pressures are within spec, system, cold and warm. I'll bet if set the cold control pressure to the low side of spec the hard cold start would go away.

[boyt911sc]

Mac,

Search for the posts of “Mike in FL” and “JSZ” about their CIS problems. Your erratic cold idle will not go away and will get worse as the weather gets colder. As you can derive from your observations, your WUR-090 is not working right. You need a good working WUR to get rid of that annoying cold idle warm-up period.

Tony