From what I've read here. It might possibly be that your head gasket has blown. I had a load of gunk on my Oil Filler Cap today, Cleaned it of went for a long drive hasn't came back just yet so hoping all is good. But spark plugs being covered in junk dosent sound too good.
Check plugs,wires Do a compresssion test Check plugs,wires Do a compresssion test
sounds more like ignition problem. plugs, wires or distributor maybe.
its broken. Have your spark plugs and wires checked. It sounds like you have one or more spark plugs that are not firing or are firing poorly. This may be the result of faulty wires or fouled plugs. You probably need new plugs and maybe new wires.
its sounds like your miss firing on a cylinder. take one lead off your spark plugs at a time, and if on one of your plugs the engine doesnt change pitch an tone then your missin on that cylinder, its probably jus a spark plug, or a lead or maybe your coil pack that needs changing
Maybe when they put the spark plugs in they were not gapped right or they maybe the wrong spark plugs.
sounds like a pair of wires are on the wrong plugs.
Auto Zone will check your computer codes for FREE. It maybe as simple as plugs,wires, or coil packs.
The Mazda 5 does not have glow plugs. Maybe you meant spark plugs?
Sounds like maybe you knocked off a vacuum hose. Have someone start engine and you listen for air hissing
sounds liked going cut out
A spark plug that doesnt fire or a coil that doesnt fire Try a new set of plugs and wires
It doesnt matter what the dealer charges for the plugs, its what he is going to find broke and ream you out for that other stuff.