Mysterious EPC/Engine Failure

[trojannate]

Well, I believe this is my twelfth post and I'm honestly growing sick of searching out solutions to the many problems for this car. So far they've been small, and I've fixed the majority of them, but yesterday evening was by far the most disconcerting.

I was driving my girlfriend out to a rock formation for a climb. We were well beyond the city and I set the cruise control at 70 miles per hour. No more than a couple of minutes later, the EPC light suddenly came on and I could feel an enormous loss of power.

I could no longer accelerate and as the car slowed down I pulled off onto a shoulder of the highway. I looked up the light and it mentioned utilizing a failure mode where the throttle is restricted so you can't accelerate. I'm assuming this is to prevent further engine damage.

I tried restarting the car and it started fine. No warning lights came on. So I decided to try and drive slowly. The car ran great. I went up to 40 miles per hour or so. Still no problem. So I decided to risk the highway again. No problems. I did not use the cruise control for fear it had some relation to the problem. We were close enough to our destination that I just drove there, enjoyed the evening, and had no trouble driving back home or in town.

As of yet, I have had no new lights or other unusual behavior. What I have had prior to this is an occasional Check Engine light, warning of a "System too rich" error. Due to another forum member's advice, I have ceased using STP Octane booster and the problem has been happening far less frequently, almost to the point of never occuring. The error did pop up yesterday - after nearly a week - so I figured some of the STP may still be present and I would just run another full tank out to see I can get it out of the system. So I turned off my check engine light with a diagnostic tool.

I've also thought that an oxygen sensor may be bad. Would this sensor have anything to do with the EPC light/failure?

I love the car, but it is starting to become a nerveracking concern. I never know when or where it will come up with some new, mysterious behavior that will possibly leave me stranded.

Thanks so much for any help or information you can provide. It is deeply appreciated.

[a8 tech]

system to rich can be either fuelpressure or air leak causing the broard band lambda to inform the ecu that the burnt fuel has to much or to little air (bad airmass reading or split vacuum pipe)however the lambda may be damaged from the fuel additive coating the probe.Checking measured value block 32 of the engine management will indicate the long term fuel trim readings(you will need vag com)the readings should be +/-10% a high reading genrally means airmass and low fuel pressure.