Trying to chase down the reason that on the highway, the car intermittently has trouble holding 70 MPH on slight inclines. So far I've changed both fuel filters, all the fuel lines, and the tank strainer. New air filter. Valve adjustment.

Yesterday I cleaned out the lines that go between the changeover valve on the firewall and the back of the engine and ALDA. The banjo bolt in the back of the engine was fully caked with soot. I haven't had the chance to run the car on the highway yet, but after reassembly, the trans shifted more smoothly. Coincidence? Today it's back to shifting hard on the last downshift when slowing to a stop.

Can the changeover valve itself be cleaned, or is this a replace-only item?

There are several in the Pelican catalog:
Pelican Parts - Automotive Parts and Accessories - Porsche & BMW

but none looks like what's in the car now.

Thanks.

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05 E320 CDI - 185K miles
82 300D - 200K miles (sold)