Revs after Starting

I have a 2000 Passat, 4 cylinder, that I bought used. About twice a month, after starting the engine the car revs at 1100 rpm and causes the entire car to shake and the check engine light to come on. Normally it idles at 800rpm. What is the normal idle speed for a 2000 Passat??? And does anyone have any ideas as to why the engine revs so high, at such random intervals??
Thanks for any advice!

Have the codes read.

Not sure if your problem is related to Revs too high at start. Sounds like the throttle body could be dirty and choking off mix to engine causing the engine to almost stall. This happened to my 01 Passat and had a buddy clean/replace the throttle body, I think the parts were $50.