Z3: Hesitation/flat spot
This is something that has gotten noticeably worse over the past few months, perhaps due to the colder weather. When the engine is in the intermediate phase between cold start and operating temperature, there is a significant hiccup when transitioning from coasting to very light throttle (no more than 10% input). It feels like I have pressed the pedal, released after a split second, and pressed again. It only does it once per coast/apply cycle. At full temperature under the same driving conditions, it feels like a simple lag or hesitation in throttle response. The engine responds more or less properly if I give it 1/4 throttle or more in a quick motion.
I did the Beisan VANOS seals a couple months ago which completely cured the cold idle fluctuation/stalling. I also inspected the idle air valve and throttle body, both of which move freely without sticking.
It's been a while since I've delved into the operating logic of the MDK system, but if memory serves the idle valve is used at low engine speed and the DME transitions from idle valve to throttle chamber after a certain threshold, correct? The only other thing that comes to mind (besides a problem with the transition timing) is the DISA valve. Whatever it is, the DME isn't seeing a big enough problem to trip an MIL which makes things a little more frustrating.
When I go to get my SRS light investigated I might take a stab at monitoring the DME data to see if it lends any clues.
1999 Z3 Coupe, Arctic Silver/Tannin Red & Maple
Last edited by k.merkel; 01-04-2011 at 10:04 PM.