Happy you have solved your problem but you should really post the solution to your problem at your original post referenced below. As many moderators and experienced mechanics have posted here before, throwing parts at a problem without doing basic troubleshooting rarely solves the problem and usually costs big $$$ in the long run. The search feature is also invaluable but in this day of instant gratification we all have a tendency to want the answer served up on a platter. Mark

Ultimate Idle Question

Done!

I'm having an electrical burning smell out of the vents too on my daughter's 1990 300E.
Does a 1990 300E have blower motor resistors?
If someone posts a response that looks like it would help you, I'll pass it along.

Great! Thank you!