Common enough with all LH 2.4 and LH3.1 equipped 89-up 240 and 7/9 models. (Just replaced mine recently on my 92 240 and wife's 90 745GL).

All use a crank sensor to trigger the ignition and therefore fuel pulses... the older cars like your 88 (and mine) use distributor triggered ignition, using the "hall sensor" inside the dist to provide the timing input.

Theoretically the crank triggered arrangement is more accurate as an indicator of vehicle speed.

Crank sensor in your friend's car is bolted to a little bracket in the top of the trans bell housing, right behind the head. 3-pin plug with a wire about the size of cable-TV wire comes out from behind there. Part number 271949, about $30 from FCP Groton (www.fcpgroton.com) or $40-something from your dealer. One 10mm (M6) bolt holds it in. Access sucks. But that's just my opinion.
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::: Rob Bareiss, New London CT ::: 92 244 M47 211K ::: 90 745GL M47 273K ::: 88 245DL AW70 190K ::: 84 242DL Project ::: 70 VW Bus ::: 70 VW Pickup Project ::: 71 VW Notchback :::