My 380SE did the same thing you are experencing. I reflowed all of the solder joints on my overvoltage relay. That fixed it for a while. Now My Idle control unit gives me trouble when it gets hot. It must have a bad solder joint also. Board expands when it gets hot then no more contact. Then high idle. Seems to be a common problem with this erea of cars. I will try to reflow that unit soon will let you know how it went. $220 for a rebuilt one on fastlane. I can spend some time soldering for that amount. You can take the idle control valve off and clean with carb. cleaner then spray wd40 in it. Helped mine to life. Good luck.