Those could be symptoms of other problems also. If a new plug cures it, then look at the old one carefully with a magnifying glass. The element can get distorted and change shape, and that affects the run. If the wire touches the side of the chamber, it shorts out and G force can do that. There is the phenomenon of "taters" growing on the element. I run idle bar plugs because that give carbon a place to attach itself before it gets into the chamber. I have seen glow plugs with so much carbon on the idle bar that you can hardly see the element! To get an idea of what to look for, just start regularly checking your glow plug under a glass. It will all unfold right before your eyes. I tell people that plugs aren't an exact science. They may last one run, one week, one month or one year. Just try and stick with one or two known good brands that you have consistent good luck with. Thunderbolts aren't around anymore, but my firstchoice has always been Glow devil R/C longs.
   Type at you later,
    Dan McEntee

Rossi, Fox and Fireball glowplugs are at the end of their life cycle, when still new in the pack.    Steve