M20 high gas consumption

[rbeaud]

Until recently, our 90 525iA had been using approx. 21 mpg. This has recently changed to 16.5 mpg. It has new plugs within the last 6k miles. The head gasket was replaced and lots of other stuff too. The cap and rotor have some carbon build-up and have manufacturing dates back to 1999. The exhaust is completely rusted out (lots of holes from salt).

Will replacing the cap and rotor fix the consumption?

I am also curious that the OBC continues to show 21 mpg. What goes into the OBC computation?

Cheers,

Roland

[DL-]

When was your last tune up? Sounds like you're ready for one. I'd start by checking for O2 sensor, injectors, fuel pressure regulator, spark plugs. Cap and rotor by themselves probably won't do much...

Dennis