Car gags when idle

Hi Guys

I have a problem with my 2009 Fiesta clocked with over 200k on mileage. For this I will put what I have experienced in some sort of sections over the past month.

First of, when I get into the car it runs fine, after 20 minutes into the drive: 

Section1:

When I was moving on a higher speed (between 130-140km/h), the engine light check comes on (flashing) and when I try to push on the gas it has no power. As soon as I stop (I could feel the car vibrating baddly but softely) and switch-off and on engine light dissappears. After this, I usually cruise at 100km/h on max and I reached my destination with no problems, this was a 2 hour drive. At this point, the car never gag'd  if its idle. I also noticed that if I changed my gears after 3.5rpm's the car doesn't gag when changing gears.

Section2:

I was going on a 5 hour trip and again as soon as I reached 120km/h the engine light came on (flashing), luckily I was coming to a stop and the engine light dissappeared without me having to switch off the car. Then when I reached 120km/h again, the light came on (flashing) and when I stop (I could feel the car vibrating baddly but softely) and switch the engine back on, it dissapears. I then decided to cruise at 110km/h max then the light never came on until 3 hours into my trip. The light came on and stayed on (not flashing anymore and when I stopped the car no longer vibrates, its running perfectly) even when I switched on and off the car. The car drove fine at 110km/h with the engine light on for close to 3 hours. When I reached my destination I switched off my car for about 20 minutes and the engine light dissapeared when I turned it on. It never appeared that day until until the next day on my way back.

Things I have noticed:

• If I change my gears after 3.5 rpm's no gag
• If I am over 30km on gear 3 (mostly when I turn) there's a gag after the turn
• If I rev the car softly, I can feel a gag right immediately after pressing on gas padal (almost as if I have to keep rpm's above 1.5)
• After 20 minutes drive, there's a gag (or a bad soft vibration if you may).
• If the car starts to gag, there's almost a delay in power in gear 1 - 3 between 2 and 3 rpm's

I took the car to Ford where it was serviced 2 months back to have a look at, they told me my throttle body & clutch are the cause and quoted me some R16.2k to replace. 

I hope someone who has experienced this can somewhat point me in the right direction.