Help! Check engine light

[Michael McLaughlin]

The patient: 99.5 A4 Avant Quattro 1.8T.

The complication: I'm 300 miles away from home this weekend and don't 
have my usual tools and manuals. It's also the weekend, so parts 
counters have limited hours. Also, I'm supposed to drive home tomorrow.

The symptoms: This morning about a minute after firing up the car and 
leaving the house the engine started stumbling badly and the check 
engine light came on (flashing). Being close to home, I limped the car 
back and parked it. Thinking it might be a coilpack (or perhaps the 
power output stage/ignition control module), and thinking that the 
local VW dealer had limited Saturday hours, I got a ride to the dealer 
and picked up a coilpack thinking I'd replace the faulty one.

Upon returning, I started the A4 to move it into the garage to work on 
it. The CEL was solid, not blinking like before, and the car ran fine. 
I then drove it around the neighborhood for a few minutes to see if the 
symptoms would reoccur; they did not.

I then decided to return to the dealer and buy the other part just in 
case it's what I end up needing; fortunately they had a decent price on 
an aftermarket one. When starting the car again, there was no CEL and 
it ran fine. On the way back from the dealer, the car stumbled briefly 
and the light came on solid again, but after about two seconds ran fine 
again. The light stayed on.

I'd love to just replace the bad coilpack and be done with it, but with 
the car running fine (and no VAG-COM access) I don't know which one is 
bad. Aside from keeping the coilpack and ICM in the car with the 
appropriate tools in case of a roadside repair, does anyone have any 
suggestions for what other steps I might take?

Thanks,
Mike