Hello all,
I have an '89 740 turbo wagon. The tach twitches regularly, usually twitching up to around 2000 or slightly higher rpms, then back down to around 800 - 1000. Sometimes it twitches higher and usually eventually dies as the idle drops down drastically after a major twitch. This will happen at idle with the car in park and will also happen in drive. In drive or in park giving gas during a sub - 800 rpm drop will often keep the engine running. From research what research I've done it would seem that maybe this has to do with the Hall sensor or perhaps ignition module, knock sensor, or radio suppression relay. I don't have a multimeter and frankly I get frustrated fairly easily by this sort of mechanical failure so I'm not willing to spend too much time figuring this out before I take it to the mechanic. If I can spend some money replacing a few obvious things the car will be better off even if I don't manage to fix it, since at 156,000 miles stuff is bound to start failing. So, my question is which part or parts are most likely to be causing this jumpy idle/dieing? What should I go ahead and buy. I'm willing to get the distributor plate with the Hall sensor since that's the most expensive part, unless it's the ECU. Also, the car has new fuel pumps, relay, cap, rotor, wires, plugs, battery, and a freshly-cleaned battery negative ground. Thanks for you help, sorry if this is a bit long-winded.

Matt Campbell