Hmmm... doesn't sound all that different than the problem I'm chasing, either.

At least I'll have a loaner LH in my hands tomorrow.

Then, after that fails to solve the problem, I guess it'll be an intake refresh, on the assumption that the ISV is shot.

I'll be really interested to see whether an LH swap fixes the problem you're chasing.

 

I will check the grounds on the throttle wheel bracket. Thanks for reminding me.

 

IT'S THE LH.

Swapped mine in and it runs perfectly on a test drive. Got fooled a little bit as when I plugged his LH back in it ran pretty well...for a minute, then the same symptoms.

So, not quite the classic failure mode (injectors clicking, generally won't run, etc.) but I think this isn't the first time the primary effect has been poor gas mileage, then a rich, surging idle with maybe a few other odd behaviors (dead transition, slow idle, dies occasionally). Need a rebuilt LH fast.

 

So, I gather, one lesson - if the O2 sensor is bad, disconnecting it should make a difference, according to a post by John in another thread. I had that backwards. Not had a bad one before (or this time) - I changed mine at about 150K miles.

 

When I plug up my O2 sensor, my car goes haywire. I guess it's bad.

 

You could check the sensor with a voltmeter. Once the car is warmed up, the O2 sensor voltage output should oscillate between about 0.1 volt and close to 1 volt. Check the single pin inside the plug versus ground. If it does not oscillate, that may be a good sign the sensor is bad. In the current case, it oscillated. Maybe John or someone else who knows this stuff will advise.

 

At least we know it's the LH now. Great to know it wasn't that difficult to solve (I think).

 

I'm happy you found the problem!

I hope that's a good omen... (for selfish reasons).

I'm within 24 hours of finding out whether or not I'm in the same boat. Hope I am (at least it's an easy fix).

 

Makes me wonder .. how many odd, irregular behaviors might actually be a degrading LH? Wouldn't be interesting to 'swap for a day' with another 928er just to see if your car runs any differently?

 

Bill, it sounds as though the O2 loop circuits in the LH are faulty. That would explain why it didn't respond correctly when you disconnected the O2 sensor. Although checking with a meter on the sensor output is useful, you really need to look at the injector pulse widths when sensor is conectd and then disconected to see what is really going on.

Louie has stock of my rebuilds.

 

I bought the JDS rebuilt for my 90' S4 from Louie. His price included return shipping. I shipping the core to him first.

 

Sent a note to Louie via his website requesting a rebuilt LH.

 

JDS rebuit LH via Louie received and installed. Problem solved.

So, this was bit of an odd failure. Gas mileage was down. Then the idle began to surge and stall but otherwise the car drove reasonably well with only some hesitation on transition from idle to being on the throttle. Somewhat rich idle based on some (not heavy) black smoke from the exhaust. Consensus - failed O2 circuit.

 

Bill,

Glad it's taken care of. It was a puzzler for a while.

 

yours and Ed's problem seemed identical. I hope Ed found his problem too..thanks for the post , this will help us all in the future