Whatever workshops they open, I have zero confidence on their workmanship, etc. Got degree but lack the machines & tools to do the precision calculation and most importantly, the material required to make proper intake hose will not be able to come up with anything close to carmakers tech & precision.

You are the fool here, stop trapping people with sweet talk that they could tune up their cars without worries. 1 wrong move and that spells the end of his car. Stop using the word 'Beh Tahan". Go to toilet then.