99 A4 2.8 quattro 5sp 83k

My dealer (independent) finished the timing belt service yesterday.
The drive home was fine. During another drive an hour later, I
experienced very significant hesitation--staccato like power drop-outs
while accelerating in 2nd or 3rd gear between about 2000 and 3000 rpm.
Minutes later, the check engine light starting flashing, then went to
continuously on. Fine above 3000 rpm. Made it home--never seemed like
it was going to competely die.

[Service consisted of replacing timing and drive belt, water pump,
thermostat, tensioner, belt roller, front camshaft seals, flushed
cooling system, Audi G-12 coolant added.
Compression test: all cyls 180 psi, except cyl #6--175psi]

Drove briefly later last night. same thing. Then again once more. This
time I drove the crap out of it, and the problem seemed to totally
disappear. CE light went out.

Extensive driving today. 90 F outside, 225 F oil temp (typical). That
particular problem has not returned, but I am noticing some similar
hesitation--stumbling-- around 2000rpm while even gently accelerating
in 2nd or 3rd gear, and also accelerating from a stop in 1st. This is
intermittent.

My dealer's apprentice did say that he spilled some coolant on the
engine, somewhere around the right-rear portion of the engine.

Ideas on this one? Ignition, fuel problem? I've not talked to my
dealer about this yet. I wanted to be armed with some knowledge before
doing so. Googling revealed little.
Dave

Al,
Yes, it looks like that is the problem. Compressed air solved much of
the problem. I still get occasional , brief sputtering, but it is much
better. Thanks.
Dave