'97 C280. Mon: new water pump. Tue: CEL is on! Ideas??

[RProsser]

Hey all. Quick question:

Yesterday, I changed the water pump on my 1997 C280 (88,000 miles). Straightforward job, no real drama.

Today I did a few local test drives (total of 50 miles or so). The car started, re-started, and ran well. Then, all of a sudden, the idle went rough and the CEL (check engine light) came on. I *assume* it's related to my recent work.

Notes:
- I checked the tiny vacuum hoses and electrical connectors in the area of the water pump. All seemed intact.
- I did not bleed the system of air because I could not find a bleeder valve, so I *assumed* that is not necessary. Can an air pocket trigger the CEL?

Any relationship between a new water pump and the CEL?

Your advice is much appreciated.