You may have a bad ignition coil. I had a similiar problem few weeks ago and replacing the ignition coil got rid of it. (I bought a used one for about $35).

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Zorin

'88 Benz 420 SEL
'79 Porsche 911SC ('87 Carrera Engine)
'00 BMW 540 Sports Package
'99 Land Rover Discovery

86 300E - Manual (sold)
88 260E (sold)
84 944 (sold)