Hello.. I am a new member with a 190E I picked up for $200. Trying to make it idle better. Here is what I am working with.

Idle: Car runs rough, is missing and has rich odor coming from tailpipe. Idles pretty consistent at around 700 rpm. Has no problems starting.

Driving: It appears to run well and have plenty of pep under normal circumstances. I have only driven it about 15 miles and have never driven one before, I am not sure what to expect.

Observations:
I was trying to make sure all the cylinders were firing, so with it running, I started pulling off plug wires at the plug. When I pulled #4, the engine operation didn't change. When pulling 1, 2 and 3, there was a noticeable difference. I tested the compression on #4 and it was around 110 pounds (all other spark plugs in place). I have pulled the #4 plug and it appears to not be burning any fuel.

Replaced/Worked on:
New spark plugs - New Rotor - Removed/Cleaned the AIC (did not test it) - Inserted two other test fuel injectors in cylinder #4 - Checked for fuel at the #4 fuel injector - Checked vacuum lines - Swapped #3 / #4 spark plug wires to isolate possible wire issue - I saw conflicting information about the firing order and switched the #3 / #4 plug wires... which somehow made no difference

Next Actions:
I am going to try a new distributor cap - Compare #4 spark plug with others

If you have any insight to this, please let me know. I know engines pretty well in general, but not this beast. Thanks for any input!!!