keyboards are 2 layers of plastic film with tiny electric contact, separated by a third layer of plastic film with holes on the spot of every single key.
when you press a key, the top and bottom plastic are pressed against one another inside the hole of the middle layer, and the electronic signal going from the top to the bottom layer tells your computer that the key is pressed.
problem is: separation is the same as an average good quality book paper sheet, or maybe the same as the aluminum sheet that makes a soda or beer can. also, the electricity that goes trough your keyboard is extremely tiny, and sensors are VERRY sensible, so your air battery can lasts longer.
So even if you have a single hair touching those circuits, your keyboard would "break" the same way it breaks when you spill coffee or whatever liquid; even after the liquid dries, the coffee and the sugar are probably still there "pressing" your alt key.
solution: (this will probably void any warranty) open your computer carefully, remove the keyboard, dismantle all keys one by one, separate the plastic layers with surgical precision so you don't cause any ruptures to the electric "wires", then wash everything with a lot of water and very little mild soap, take extra care to remove ALL the soap, leave everything to dry in the sun (you know electronic components don't like humidity, right?) assemble everything together with "just-washed" oil free hands (don't touch the inner part of the sensors now).
Doing all this, if you have any luck your keyboard might work 100% again... or maybe you might make it stop working entirely, who knows? =)
if you have some money, then backup you computer, go to the applestore and tell them you want to buy a new keyboard, because you broke the current one.
they shall give you a brand new (refurbished?) one, and charge you only the new keyboard. or they might give the same one back to you, who knows? haha.
If the product you used to clean the keyboard was wet, you could have created a short in the keyboard or perhaps even corroded the contacts under the Control key.
Two outcomes:
- You give it a few days to dry out.
- You buy a new keyboard.
Hopefully #1 will take care of it for you!
In the past, I've scrubbed nasty, dirty keyboards with a firm brush and water under a bathtub faucet and then let the keyboard dry out for a week. However, that was not the low-profile "laptop like" keyboard that Apple has been providing for the last decade, so I can't say that I've done it on modern Mac keyboards. But that all being said, the key thing is that clean water (NO SOAP!) should leave no residue (unless your water is very hard) and as long as you don't introduce electricity into the mix while it is still wet, you shouldn't be risking creating permanent short circuit damage.
Best Answer
Sounds like your problem may be with keyboard, not software. But worth a try is the following. Go to system preferences / Keyboard and click on keyboard tab. see image below.
There is a slider to adjust the delay time between keys. Make that time as short as possible. This feature is for holding down a key and having it repeat but should work in your case too.