I've had my Focus for almost 2 years now, however recently I've had a weird electrical problem with it, it first started a few weeks ago and has occured 3 times since. I'd just be driving, then the car would almost cough, where you'd have a stable throttle but it isn't delivering power smoothly, then the TC light would come on, following that a warning would come up saying the hill start assist is not available. The whole time the throttle response would become strange, it would no longer be so lumpy however the first ~40% would not do much until you put your foot down and it picks up properly, like a weird limp home mode even though according to the car nothing is really wrong. I was able to catch it once and go into the car's computer in the driver assist page where TC was still ticked as if it were on, despite the TC light being on, and in the little 'system check' panel thing, it would still say "all systems normal". If you just turn the car off and back on again then all the problems disapear, but I dont like the fact that it's started out of nowhere and has reappeared on a few occasions. Another small thing is that the first time it happened, it turned off my start stop, since the light for 'off' appeared, but it doesn't work anyways (I don't particularly event want to use it) and in subsequent occurances of this problem I haven't noticed if it happened again since i've been too busy trying to find somewhere to quickly stop and restart the car. I'm taking the car in on Saturday but I'm worried if they might not be able to find anything since there is no engine warning light so it might not even flash a fault code, so if it doesn't happen while its in the hands of the mechanics then it might be impossible to diagnose. Anyone had anything similar or have any thoughts on what might cause such a problem?

As it is an electrical problem start with the battery. Measure the voltage at the battery terminals with a multimeter in the morning after the car has been standing unused overnight. The battery might need charging or replacing if it is more than a few years old. The alternator on these prioritises saving fuel rather than keep the battery fully charged.

Set yourself up with FORScan and the next time it goes into fault mode read the codes then.

That will give you a better idea of what is causing it