I took the car to a local independent VW shop and they thought it was the pump. Replaced the pump and the problem persisted (then removed the new pump). They said it must be the ECU, but they don't do ECUs. (BTW: existing ECU is stage 2 rocketchip, 5+ years old, actual age unknown).
I borrowed a highly tuned ECU from a buddy and the car ran without dying, but the idle still fluctuated (** This was after warming the engine up and running for ~10 minutes. With my own ECU I'm sure it would have died). The fact that the idle fluctuated indicates that there's still a problem and for some reason (* more on this next) the tuned ECU made it continue running.
Tonight, I drove the car for 30 minutes with my ECU (stage2). Here's what happened:
- While warming up, the car does not die and the idle is dead on at 908 rpm
- First 5-15 minutes of driving after warm: I must carefully let my foot off the pedal to let it slowly approach 900 rpm. If I take my foot off the pedal from >1500 rpm the rpm will precipitously drop below 900 before it tries to recover, but it will die.
- After 15 minutes at temperature: Even a small reduction in rpm or idling below 1200 will cause the car to die. To keep the car going you have to keep your foot on the pedal.
- If the car dies in motion, then I put it in gear and release the clutch and generally it will restart.
- If the car dies while at rest, then it is hard as heck to get it restarted. Pedal all the way to the floor and long starter engagement, maybe 30+ seconds, will generally restart the car. Car will restart with ease once it cools off.
- During the last 15 minutes of my 30 ride, I lost it 5 times (2 in motion) 3 while nursing the pedal trying to keep it idling while coming to a stop.
So, does any of this make sense? Any suggestions?