okay - this will sound a little strange, but hey - I was right about it not being the gas, and right about the problem being in the ignition so my credibility should be good.

remove the cap and rotor. take a T30 Torx wrench and remove the bolt that lives behind the rotor. Make sure the bolt is completely healthy and then reinstall it. I recently purchased a 300e at a huge discount because the owner had spent thousands at the dealer and couldn't resolve this intermittant problem. The bolt was cracked, which caused the rotor to have a little bit of play. This wore down the contacts and increased the size of the gap. So a new cap/rotor made no difference after a few miles. Check out my DIY on resealing the top timing cover for picks of the bolt and tips on cap removal.

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89 300te 222,222
92 300e 190,000