Bad taste can be caused by a dirty coil, clogged wicks, a burnt wick, or your cleaning process. I haven't cleaned coils since CE5s - replaceable coils are cheap enough now that I just replace them. The method of dry burning coils to get the gunk off them stopped working when manufacturers replaced ceramic wicks with cotton - cotton burns and you can never get that burnt taste gone without rewicking the coil. The solvent you use to clean the wicks is also quite relevant - you want something like Pure Grain Alcohol that won't leave a residue ( I know people who use IPA and others who don't trust it - or their patience in waiting for it to fully dry).