Date registered: Jul 2004
Vehicle: 1991 500SEC sub 50K mi. 1987 560SEC Now 150K mi. 2018
Location: Boston, MA area
Mentioned: 19 Post(s)
Quoted: 418 Post(s)
I'm leaning with
"possible vacuum leak sealing itself once expanded by engine heat. " (G.T.)
and its getting worse..
I bet you can find by spaying carb cleaner… WD40… NOT Silicone spray .. Not Brake Cleaner… something flammable with one of those little nozzles..
When you reach the vacuum leak the engine RPM will change.. smooth out something along those lines..
Hey good luck man,