If I recall, it was the rubber elbow that attaches to the aft passenger side valve cover that was in the way of sliding the harness connector through the firewall. I ended up having to run the wires through from the back of the wall because I couldn't move the hose and didn't have a replacement hose at the time. So, it wouldn't be a bad idea to order that hose.

Other than that, just be careful not to disturb the ETA wire harness running across the top of the engine, just in case it's in bad shape too. You'll see what I'm talking about when you get the air filter housing off.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles