I call myself trouble shooting the lope my engine has which I think is causing a small annoying vibration any time speeds are 15 to 40 mph, with feet of diesel peddals. It will stop any time you depress pedals, and starts again as soon you release them. I raised the hood with eng running and raised eng speed to 3k. Release and eng whips twice on the way down to a smooth idle. I pulled of a cannon plug to a vacume valve at intake manifold. This cause the check eng lite to illuminate. How can we reset it.

99 TD 5067 miles.