It could be a bad O2 sensor or a bad catalytic converter.
〉 Answered on Aug 10th, 2012 by Colleen McGee, Driving Instructor at Americas Driving School
Fuel mixture seems overly rich. You may have injectors that are leaking down overnight into the combustion chamber. It needs to be diagnosed by a qualified technician to be sure. Do not think that adding injector cleaner will help.
〉 Answered on Aug 10th, 2012 by Jo An Holt, Automotive Journalist at Holt & Associates
David, there could be a few different causes. But the rich smell is from your fuel running too lean, causing excessive burn off of fuel in the exhaust. Vacuum leaks, emissions and the fuel supply system could all be possibilities. My best recommendation would be to have an ASE certified technician properly diagnose the problem to avoid the costly expense of trial and error with replacing parts.