My '88 300E (Gas) failed emissions with an extremely high HC and CO count - in Colorado.
I have changed the filters and ran "Seafoam" through the tank in an effort to get me through again. The diagnostic shows that the car is great but it still reads high - any suggestions as to why or what will help?
Havent changed the HCsensor yet - will that help? If so, what does that entail and how expensive and time consuming is it to do this?

 

I am not a expert, but I found useful information at http://www.aa1car.com/library/2000/ic60032.htm. High carbon monoxide (CO) emissions are a telltale sign of a rich fuel mixture. Elevated hydrocarbon (HC) emissions usually indicate ignition misfire due to fouled spark plugs or a bad plug. High HC emissions can also be caused bybad compression (burned valves), lean misfire (check for vacuum leaks, low fuel pressure or dirty injectors), or rich fuel conditions (excessive fuel pressure, leaky injectors or a dead O2 sensor).