944turbeaux

Hi everyone, I wanted to see if anyone had thoughts about the problem I faced this weekend. At a track session, the car was running well, but about 1 hour after the session I started the car and noticed erratic acceleration. It holds idle smoothly but when I apply throttle it stumbles and jerks and pops. However, under full acceleration, it operates normally and has full power. This is my first time taking it to the track so I wonder if it exacerbated a gremlin. I have a setup similar to the Autothority MAF kit (Pro-Flow) with custom chips. Looking at my AFR (not wideband) it appears to oscillate from normal 14 to lean off the scale. I cleaned the MAF, but saw no change. My fuel rail is reporting the 50psi that it typically is at (replaced pump and filter this year). I have ordered a new TPS to try out as well as some speed/reference sensors and a DME temp sensor to try out. I am not sure if there are any vacuum leaks, but I thought it would be odd to have one if both idle and full throttle on boost operate normally. Any thoughts?

boost feen

I would test the intake tract for any vacuum leaks, second i would double check the reference and speed sender gaps they need to be perfect to run well at all temps, third I would double check all wiring harness ends at every plug connection to make sure there are no shorts. This requires pulling all boots back to the close wire ends where they go to plugs.

Bill

I am Curious- Did you find the cause of the stumble?

944turbeaux

Yes I did figure out the issue - my cold air intake was routed behind the fender well, and on the track day my tire bottomed-out onto the fender/filter (sticky tires), which caused the filter to move and get starved of fresh air. I re-routed the intake to be inside the engine bay with new silicone tubing and a new filter and it runs great now.