TwinTurbo.NET: Nissan 300ZX forum - It sounds like an issue similar to one I had with my old TT
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Subject It sounds like an issue similar to one I had with my old TT
     
Posted by Gordo 96NA Daytona on April 17, 2018 at 9:02 PM
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In Reply To Revs not dropping immediately to idle... posted by GrecV2 on April 17, 2018 at 09:37 AM
     
Message It relates to the ignition timing map tables wherein the ECU is programmed to follow a gradual reduction in timing when the TPS signal goes from OFF IDLE to ON IDLE. e.g., when you let off the gas.

There are two step down timing plateaus worked into the timing tables, one in the mid to high twenties and another at twenty degrees. They are designed to smooth the transition from OFF IDLE [cruising or coasting] when the timing is 30-40' down to the nominal timing of 15 degrees in ON IDLE mode. Maybe a half second at each step?

In my case timing wasn't holding long enough at each step down and the symptom was a sudden engine braking... almost a jerking action going from a nominal 30-40' almost instantaneously down to the 15 degree hard idle status.

If your issue is electronic and relates to ignition timing, it could be the opposite of my problem in that it could be be your ECU is holding the timing at these step down map tables too long in spite of the fact your TPS is signaling the ON IDLE timing values should commence.

I never solved my issue as I was using a Zemulator, and I couldn't get Ash to help me work out the Timing, TPS, Idle configurations and reconfigure the tables. Not long after, I sold the car and the problem went with it. However, the work around was to add a miniature pneumatic piston actuator to the end of the throttle cable that mechanically slowed the last few degrees of throttle plate closure and this smoothed the transition enough to meet my goals.

This is far fetched, but I had gone through all of the suggestions made above, and the issue remained. The one thing I didn't do, was to exchange ECUs with a car know to not have this issue; and that would be my first suggestion.

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