Golf IV / Jetta IV :: 2002 VW Intermittently Starts / Jerking Feel And Sound Of Misfiring

The car is a 2002 VW Jetta, automatic 1.8t GLS. 146k miles on it. Has an external amp/sub wired up by my brother who is an MECP certified tech and has been doing car audio and overall Audi/VW for years.

I was driving, nothing out of the usual, this car is my daily. Stopped because of traffic and my car died in the middle of traffic, the gauges (tach, speedo, gas, etc) spiked immediately, which I assumed meant loss of electricity, but my radio, headlights and everything else stayed on. The oil and Battery lights came on as well. Tried to start it, it was trying to start, and was cranking quickly, but wouldn't turn over. I got it out of traffic. I pulled my amp power and the car turned over and started driving like normal, so i figured there had been a short in the wire and that was what caused my issue. Drove about a half mile down the road, car shut off again, car said it needed oil this time. checked the oil, there was plenty, but i put more in to be safe, and it turned right over and i managed to drive it about 30 minutes and got it back to my house.

So, my brother and i look the car over, couldn't find anything really wrong with it, so we took it out for a drive, no problem at all for the first few minutes of driving. Car shuts off again, doing the same thing, but just the battery light came on. My brother jumped my car, it turned over, but as i started to drive it, it was a lot more rough with shifting (possibly tied to electrical problems because i know there is a solenoid cluster for automatic transmissions), i mean you could actually hear the gears shifting and the car was kicking through each gear, as well as my driver side headlight not turning on (just installed brand new xantec 6k 55w HIDs, but i dont think those are the problem because the problem started before i installed the HIDs) and died 3 more times before i got it home, having to jump the car every single time with symptoms the same as the first time it died without the oil light. Another thing i noticed is that the car seemed to only die when i hit the brakes and the car went to low RPMs, which lead me to believe a major vacuum leak. At idle the car also seemed like it was misfiring even though the CEL was not flashing, it just had the jerking feeling and sound of misfiring.

My brother and i take a better look into the bay area, and noticed that the top of my engine was covered in oil, from the intake manifold back. I know my car has been leaking oil, but not spraying it. We pulled everything apart, totally cleaned the engine bay area out including MAF, spark plugs, coil packs etc. The engine bay area looked practically brand new. Now i do know that my car has had a vacuum leak (no boost gauge to tell how bad, but the brakes were a little bit less responsive and the car was acting as though it was misfiring despite the fact that the coil packs and spark plugs are brand new) and we couldn't find where it was, and we thought that maybe that was the problem. A lot of the vacuum line was dry rotted and falling apart and some parts weren't even connected anymore from that, which we replaced all of the line we could find to eliminate the idea of a vacuum leak causing the car to die when i hit the brakes. We also tested the battery with a multi-meter which read variably between 13.8-14 V, which if i understand correctly is within normal range, but oddly enough we put the battery through a stress test including turning on defrosted, turning sound system back on, headlights on etc, and the voltage didn't read much different, still bouncing between 13.8-14.

When tearing things apart, we also found that the starter solenoid was unbelievably loose due to a bad transmission mount, and one bolt was missing, so we were thinking that could be arcing causing the problems, but when the solenoid was tightened down, the problems still persisted.

Started the car, let it warm up, and it seemed perfectly fine. I drove it into town without problems, but forgot my wallet at home, so i had to turn around and go back. Almost made it home, the car died while stopping at a stop sign. Tried turning it back over, nothing the first 3 times, let it sit for about 5 minutes and the car turned right over as if nothing was wrong. Died again when i made it into my driveway about 0.5 miles away and the symptoms repeated until the car finally just turns on like normal now, but the idle is at 1100 RPMS (not sure if related or not) even though the car is at the optimal temperature. I tried driving it again after the car starts normally like it does now, but it just repeats the symptoms that it has been, cutting off but leaving the stereo, headlights etc on. I managed to get it back in my driveway.