Proton Preve Exec (IAFM) engine sound issue

Symptoms

Usually if the engine making sound like an old diesel engine (like a small lorry engine) and you feel like the car have no pickup.

Possible cause

The cause might be because of broken butterfly valve in the intake manifold compartment.

Solutions

Usually the intake manifold have to be replace. Not so sure whether the butterfly valve can be fix without replacing the intake manifold. I have found some blogs / websites saying that the intake manifold can be replace with the Iriz's set. 

I had changed mine before with the original set. If not mistaken, it cost about RM 800. Iriz's set is a cheaper like about half the price.