Can only get up to about 20mph for first 5 minutes?!?!

My wife has a 2000 Jetta with the 2.0L and it starts fine but if you try to drive down the road it only gets up to about 20mph and then sort of sputters and misses no matter how far you press the petal down. The engine light will be fashing too.
Then after about 3-5 minutes, it stops flashing and the car runs fine...

I figure it must be something electrical because it isn't very consistent and it very suddenly goes back to normal.

It has about 85,000 miles.

Any ideas.....

Have the codes read by someone with a scanner, most Autozones & some Advance Auto Parts stores will do it for free.

have you done a tune up on it?
could be a bad wire, mine did the same thing but it got worse as time went on, finally took it in and it was a bad spark plug wire.