I've got a 2000 Explorer Sport (2dr) w/ 4.0 X-Vin OHV with 126xxx miles and I've got a few engine issues I'm trying to diagnose, wondering if the issues I'm having are connected - mechanic hasn't been a big help. Here's what I'm seeing: - Check Engine Light has been on for some time, scanned codes, says I have a large vacuum leak (can't remember what the exact code was). Per mechanic's suggestions, I've replaced the gas cap 2x, hasn't fixed problem. I'm wondering if there is a valve in the vacuum system that has gone bad? - New Motorcraft plugs & wires. Plugs have needed replaced at least once a year. Center electrodes get worn down to almost a nub/fine point and cylinder will start missing badly. Usually the offending plug will be on the lean side and codes will indicate a cylinder is running lean. Every time it's happened, it's been a different plug that goes bad - never in the same cylinder twice. - At start-up, truck idles rough when cold. At/below idle, idles roughly, chugs - rev the throttle in neutral or accelerate over 2000-2500, cleans rough idle out and truck starts/runs great while warm. - Slowly losing coolant from radiator, can't determine where. Not seeing any leaks or drips, doesn't leak while sitting. I will occasionally smell a puff of coolant via the heater/ac ducts when starting the truck (mostly when truck is warm), but that's about it. Truck doesn't appear to be smoking in engine compartment or excessively out tailpipe. I've pulled plugs a number of times in the last year and there has been no evidence of coolant on the plugs. Truck has not overheated to my knowledge. Wondering if I have a leaking heater hose or something like that? Got my fingers crossed, really hoping it's not a head gasket leak - need to run a compression test soon.