Then don't do it yet.

Carbon build up is due to cars EGR system. It recirculates exhaust gas back into the intake at low load for the engine to run cooler and have cleaner emissions. EGR is not new, even on my old 1989 gallant has EGR but I blocked it with a blocking plate. The PCV system also may channel oil fumes back into the intake and can cause intake fouling. Turbo GDI engines generally will have higher carbon build up as compared to N/A engines.

With no more port injection, the intake valves don't get cleaned hence the carbon build up. Toyota does is correctly with their own D4S engine with both port and direct injection.

So if you drive a lot at light loads then you will get more carbon build up on the intake as the EGR typically functions at lower engine loads.

Only way to check is to remove the intake manifold.

If your carbon built up issue is not severe, sometimes you can just clean it with carb cleaner. A diy job if you are handy.

This post has been edited by jaycee1: Oct 22 2025, 10:14 AM

The main reason is PCV valve system that allows the engine oil fumes to return into intake. If exhaust gas itself the carbon wont stick (see your exhaust), it need oil or contamination to stick with it and solidify.
Thus why it is recommend to fix oil cache tank for direct injection engine to trap those oil from going back into intake, but still it wont total eliminate (only delay).

I guess you've never seen a clogged up egr before.

At low rpm low load, and thus low intake velocity or in the case of GDI, improper burn, the combustion charge will turn to soot and gets re circulated through your EGR. That's what the EGR is supposed to do. Generally, GDI goes to lean burn up to 20:1 so soot is less of a problem but it does happen.

Also all engines will burn a little oil through the rings. Some more, some less.

I already mentioned the secondary cause which is the PCV.

Most EGR issue seen by my mechanic are usually owners driving pattern & poor maintenance, my dads own an e90 320D until today never heard of him said about EGR stuck or blocked due to soot this is because my dad usually drive his ride outstation, on highway a lot and only pump Euro5 B7 diesel.

My mechanic place those who always complain of EGR issue can see a pattern, like to idle long period, usually city dwellers and also poor maintenance (engine oil use cheap and drag long period, (petrol engine) spark plug use low quality or wrong spec., dirty air filter etc or like to pump cheap diesel(for diesel rides)). If your ride seen a lot EGR issue, you need to check back your engine requirements like engine oil spec. spark plug types (or diesel fuel grade for diesel rides) and air filter, usually these 3 if not taken care will not help in improving combustion thus more soot = EGR faster stuck.

This post has been edited by littlefire: Oct 24 2025, 09:57 AM

My point exactly. Which unfortunately covers most city driven cars and drivers. Long idle. Short drives.

EGR on modern GDI cars are to minimize NOx emissions, (GDI tends to run leaner and hotter therefore increase NOx) and the EGR cools the charge. Unfortunately a cooler intake charge tend to also lead to carbon build up.

What doesn't get stuck at the EGR will eventually end up in the intake and valves.

That said, newer cars tend to have more accurate fueling minimizing this issue, but it does happen.

Anything that goes through your intake, be it EGR or PCV will eventually end up fouling your intake ports without something to wash them clean.