I just had a similar experience with a 190D that I'm resurrecting for Fuel Mileage.......very squirrelly over 50 MPH......

I used a couple of jackstands.....got a couple of long and...straight 2x4's.....set 2x4 up on jackstand and lay it up against the center of both tires on each side 2x4 should contact both sides of the rear tires, and the rear side of the front tire, with the front sides of the front tires just a very, very little bit of gap (toe in).......this will tell you how your car is tracking and will also tell you how much toe in/ out you have.......

Hillbilly Engineerin' 101

SB

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Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG