erratic tack/rough running '91 passat

[davidlucasbarne]

Hey, my 1991 Passat wagon has a problem that comes and goes without any obvious reason: the tackometer will bounce around like crazy and the engine will start to run rough, both missing and surging, and if I take my foot off the gas the car will either idle erratically along with the tack, idle about 200 rpm higher than usual, or stall. Also, when the problem is present the car will have difficulty starting and will turn over very slowly as if the battery is almost dead. I've replaced the ignition coil, distributor, spark plug leads and plugs but the problem keeps coming back. It was really bad in the spring/early summer, went away for a few months, and now it's started happening again in recent weeks. I don't think it's a moisture-related problem though because neither hot nor wet weather appear to affect it.

If anyone has any thoughts on this both myself and my mechanic would truly appreciate it.

Thanks!
David