I also had a code #4 pop up on my car, and it was a loose vacuum hose. I also had a code # 26, but it was a false code.

Apparently, any vacuum problem could trip a code #4 and maybe cause other codes to come up, kind of like chain reaction.

It takes several cycles for the same fault to cause the code to trip, so keep your fingers crossed.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".