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Old 05-05-2020, 02:31 PM   #1
Drives: 2011 Yaris 3DHB
Join Date: Aug 2014
Location: Canada
Posts: 8
Rough low idle : Mass airflow and misfire error codes

Hi there. I've been having some trouble with my Yaris lately and have been trying to diagnose and fix it myself. I'm a beginner at this type of stuff, I usually only do basic maintenance (brakes, oil change, etc.), but am looking to learn more.I have a 2011 Yaris HB 5 speed manual, with approx 165 000 km (100 000 miles).

At idle, it seems to stutter a bit, and the RPMs jump around a little. It also produces a pretty pronounced clicking or ticking sound, as if something were loose in the engine. This only happens when the engine is warm, and idling around 500-600 RPM - the problem disappears when the RPMs go above 7-800.

This was accompanied by a loud whistling sound which would go away when accelerating. I found a pretty big hole in the PCV valve hose, so there was a pretty bad vacuum leak. I replaced the hose, and also took the time to clean the throttle body. I thought that would fix the rough idle, but it didn't.

The check engine light and the traction control "slip" lights are constantly on. I read the OBDII codes, and I am getting :
P0100 - Mass airflow circuit malfunction
P0102 - Mass airflow circuit low input voltage
P0300, P0302, P0303, P0304 - These are misfire codes, the 300 code indicates misfire in more than one cylinder, and 302, 303 and 304 indicate misfires in cylinders 2, 3, and 4. The low idle clicking does not sound like a misfire, but I guess that could be it.

I am thinking the problems with the mass airflow system are causing the misfires. Could that hole in the PCV hose have caused a problem with the mass airflow sensor ? I ordered a new PCV valve, just in case that got damaged.

Should I try replacing the mass airflow sensor, or maybe just cleaning it first ? I also noticed the airbox has a broken clip and didn't seem to seal very tightly, could this be cause for concern ?

Thanks ! Any help is super appreciated.
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