Mark Houghton

Put your brain caps on, and let me know what you think about this one. The symptoms: During the first maybe 5 minutes of drving after a cold startup, everything is cool and running as it should. My AFR gauge shows a richer than normal mixture, telling me that the WUR is working properly. Now, 5 minutes into casual 2nd gear steady throttle, the mixture has leaned out somewhat (again, the WUR internal heating element is doing it's t hing and settling down to normal operation). However - within a couple of minutes - while just mellow steady throttle 2500 rpm cruising I begin to "feel" an ever so slight sporadic hessitation....call it a flutter in the power band. Looking at the AFR gauge, it's fluctuating to way lean for just a split second, then back to normal range. No backfires, nothing like this, just a slight rythmic short-lived hessitation. It'll do this until she's good and warmed up, then everything (AFR) is steady and acting as it should.
Long story - sorry - but these things are hard to explain on paper. Something is causing very quick swings in the AFR, to the lean side. Pressure regulation issue, fuel delivery issue, stuck injector, what?????

Mark Houghton

Now I can't believe that none of you have any input on this? One sure way to find the problem is to drive her till she breaks....but I don't like operating in that mode. Do I have all of you stumped?

Autobahn

My car is experiencing the same issue but only during the first minute of driving. It only happens when driving off from a stand still, e.g. red light. Unfortunately, I also have no idea what is causing this.

nathanUK '81 930 G50

Well, the only thing that compensates for temp when on the gas is the wur. You could try getting it checked out and modified by Brian Leask.

Mark Houghton

I think maybe I'll run some Techron injector cleaner through a tank of gas first. This is such a subtle symptom; I can't help but think that it's injector related and just not noticable until the car has warmed up and isn't on a rich cold run condition. Also, I think I'll re-check my baseline %CO at idle; it may have changed somewhat after the valve adjustment I did this winter (remember, I don't have a nice LM2 for this, just an old fashioned Gunson Gastester).
The WUR seems to be working fine as boost builds (per my narrow band gauge), so I'm not concerned in that area.