Jekyll and Hyde driveabilty - or am I nuts? (archive)

I am losing my mind. Maybe. Ok, so I've had a cold driveabilty issue for a while, (88 M5 w/ 82k) drives like crap (hesitates, lurches, occasional backfire) when stone cold, then runs fine when O2 sensor kicks in. Have checked just about everything in Bentley list: air leaks (idles fine), AFM flap, new coolant temp sensor (old one was fine anyway), compression perfect, TPS, idle mixture adjusted on a sniffer, O2 sensor checked, swapped JimC chip out. The only thing that helped it at all was to adjust the AFM CO screw all the way in. But this made the mixture WAY rich, like 8%. So now that it is set at proper CO (screw 8 turns out from bottom) the problem is back.

But wait, there's more. On any given drive, I notice a fairly subtle but clear to me difference in the way it drives. Some trips, it feels heavy, engine sounds louder, rougher, under load. Throttle response seems sluggish. Other times, it drives beautifully. But this is the kind of thing where if you don't drive the car all the time, you may not notice it.

SO I am convinced these problems are related somehow. I am also convinced I am not imagining the warm driveabilty changes. I have not tested fuel pressure, but reg and filter are nearly new. I have also not pulled injectors, but sniffer gave good HC readings, meaning probably not a leaky injector. But maybe a bad spray?

There's even more. The voltage required to make a spark is high, like 30kV versus normal 8-10kV, yet I am getting a good burn (HC reading). But maybe this points to a clogged injector? Cap, rotor, and wires are good, plugs new.

One mechanic (both guys honest, experienced) thinks its probably not injectors, other thinks could well be. Does any of this ring any bells for anyone? WHy would it drive fine sometimes, bad other times (subtle) and almost always be crappy if completely cold....

If anyone actually gives me a lead that works, the car is yours. Well, ok maybe not, but would happily ship beer "care package" your way...

Follow Ups:

Re: Jekyll and Hyde driveabilty - or am I nuts? Bob C WNC 85 635 00:40 11/05/2001 (0)
Re: Beer care package motivated! Douglas 10:30 11/04/2001 (1)
- Re: Beer care package motivated! Todd Kenyon 19:32 11/04/2001 (0)
Re: Jekyll and Hyde driveabilty - or am I nuts? Neil Deshpande 23:17 11/03/2001 (1)
- Re: Jekyll and Hyde driveabilty - or am I nuts? Todd Kenyon 19:46 11/04/2001 (0)

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