95 E320, 104992 engine, 92,000 miles, new wire harness, new head gasket

CEL on about two weeks ago. Clear codes, drive, recheck, reclear......Check again this morning. Consistantly get codes for upshift delay, EGR, and air injection pump. (diagnostic module 26, 5, and 4)

Seems very unlikely to have three problems show up at the same time on a car that gets meticulous maintenance. Then it occurs to me that all of these items have one thing in common--they require vacuum. Sure enough, vacuum hose on top of intake manifold had come loose. Reattached, problem solved.

Hope this helps someone else.