Rough Idle and stall, codes P0172, P0175, P0128, P0104

DAVID CONTRERAS

MEMBER
2003 MERCEDES BENZ C320
3.2L
6 CYL
2WD
AUTOMATIC
190,000 MILES

Been having rough idle on the car when in drive not as much when in park. Car stalls sometimes when stopped and has delayed acceleration when going from stop. Car will sometimes stall when coming to a full stop and had it stall twice when doing a right turn at low speed. I have codes p0172, p0175( car running rich in both banks) p0104 mass air flow circuit intermittent and p0128? Coolant Temperature Below Thermostat Regulating Temperature.

I changed the coolant thermostat and the error code when away added STP in the tank and the rich codes went away. Cleaned the mass air flow sensor and error code came back. For a while the code was the p0104 mass air flow only but now again all of 4 of them came back. The diagnostics on the obd2 has the MAF looking fine then dropping hard then normal, so it seems like the MAF sensor is working fine. I'm thinking there is a vacuum leak some where but don't know how to check for it on this car, don't see any loose lines (visible) any ideas?

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

Hi,

I would agree this sounds like a vacuum leak. Here is a guide that helps find these.

The best way is to take a parts cleaner spray with the straw attached and spray in small targeted areas and listen for the RPM to raise. What will happen is when the chemical gets close to the vacuum leak it will pull it in and raise the RPM.

Let me know what you find. Thanks

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge