so you removed the ground to see that it was clean? When we say check the grounds I/we don't mean go look at them as that is about as useful as looking at your vac lines for leaks. You might find it is loose but when I say check the grounds I mean remove them, inspect the wires and connectors as well as then clean the connectors and the mounting surface prior to tightening them back down. Bonus points would be awarded for taking an ohm meter ane measuring the resistance of the wire to ensure that it is as low as possible as it is possible to get cut in the middle of the wire and have it start corroding there to cause a problem.