Among other Stihl stuff, I've got an FS55 trimmer, now 7 years old. It starts and runs very reliably, and never cuts out as some I've seen mentioned on this site with coil problems. What has been happening though for about the last two years is that when the day temp gets above about 70F, the idle speed increases to the point where the engine is running at about 1/4 to 1/3 revs. I've adjusted the idle screw to its lowest setting and checked the return spring on the throttle, and on the face of it everything is as it should be, but when it's warm it won't idle. The only thing that gets it to return to idle is holding the throttle wide open for a few seconds. But start running the thing at part revs again and the idle speed starts climbing again. I asked my Stihl dealer about this and he said "What are you worried about? It works, don't it? You should be running it at full whack all the time anyway". He has a point, but I use the FS55 for mostly light trimming jobs and I don't want to run it at full clout all the time. The main point though is if the cutting head is racing round on idle, it's a bit of a pain as well as a tad dangerous. Any suggestions?