Hey guys,

So I've been trying to track down a stumble/miss for a few months. Last week I replaced the Opti, so now I have a whole new ignition system, but problem is still there... (no high rpm probs now though) SO last night I was playing with freescan and noticed that timing @ idle is jumping all over the place, 22-27*!! If I remember right, i used to see 17-21* @ idle. I do not see any knock retard. What is causing the timing to be so advanced? And why is it fluctuating so much. Timing chain?? Help me!

Dave

 

The timing advance value you see on the scanner is simply the value the PCM is picking off the look-up table (minus any retard), based on RPM and MAP. If timing is jumping around, it means RPM and/or MAP are jumping around. 18-22deg is very typical for an M6 at stock 800rpm idle, with stock programming.

 

Fred,

First off, the car does have a pcm4less tune...

Second, RPM is steady, +/- 25 rpm (usually 800-825). However, MAP does bounce a little, If I remember right it's about .300 - .310... Wha would cause MAP to fluctuate? Vacuum leak? Burnt Valve?