You might try a fuel system / injector cleaning. This is done at the mechanic, and they hook up the fuel intake system to a machine that pumps some high strength stuff through the injectors. I've known a few people that have done this and the results have exceeded what you can get with techron. Should be about $100 at an independent mechanic.

This is worth a try before you go replacing things. It will be hard to diagnose without a Check Engine light.

Regards,
Troy K.
1995 E420 83k