2011 Impreza Overheat

[thesmokinggasket]

New here but starting to lose it hoping some of you have some nuggets of wisdom.

My 2011 Impreza started overheating about a week ago at around 130,000 miles. Ended up towing her home. Currently has a rough start and occasionally misfires also overheats after about 15 minutes at idle. I haven't been driving it around due to the quick overheating issue. The code reader gave me P0172: A rich mixture through the O2 sensor and P0301 for a misfire in cylinder 1. I've swapped the MAF sensor, front and rear O2 sensors, cleaned the air intake, and changed the timing belt water pump assembly for the heck of it. The code reader says I'm running a -25% fuel trim which to my knowledge means the ECU thinks the engine is running rich and is pulling fuel. My hunch would be that the ECU is pulling from a faulty sensor and is causing the car to run lean and overheat. 

Also looked at the radiator, hoses, cooling fans, and thermostat and couldn't find any problems.

Not sure what to replace next, I could start tearing into the fuel regulator, and injectors but my gut feeling is that it's something electrical.

Any help or thoughts would be appreciated

[lmdew]

Check the radiator fluid level in the radiator, not the overflow when it's cold.  Is if full?

Is coolant pulling back from the overflow when the engine cooling down?

Does it run rough all the time or only when warm?

Compression check?

Sounds like head gaskets may be in your future.

 

[ocei77]

 

Are the fans coming on?

Are you getting bubbles in the overflow tank?

Did you recently do something with the cooling system?

If so, did you fill the block first and then the radiator or just the radiator?

[nvu]

Overheating on idle sounds bad.  Get one of those radiator fill kits where you hook a bucket to the top of your radiator cap. With the bucket filled, massage the upper radiator hose to get rid of bubbles.  Let the car warm up and spit out the remaining air bubbles.  It should be running fully warmed, with radiator fans cycling on and no bubbles.

You can force the car into limp mode to get a stable idle if needed.  With engine off, key out, unplug the maf.  Start the car, it'll be in open loop and it won't rely on any o2 sensors to idle.  The idle should be stable as the ecu injects the default fuel amount.  If idle is still bad, it's something more basic, fuel, spark, compression.  You won't be able to drive in limp mode, it'll be rev limited and probably beep a lot.

To reset the ecu back to normal, unhook the battery, hold the brakes for a while.  Hook back the maf and start the car.

[thesmokinggasket]

Filled the radiator using one of the buckets to get rid of air in the coolant system after I had replaced the water pump and timing belt. 

The problem existed before I had done anything to the coolant system.

Both fans are working properly and turning on once the car has warmed up.

I haven't pressure-tested the coolant system yet nor checked any of the cylinders.

Primarily runs rough on startup prior to the engine warming. 

No sign of oil-coolant mixing so far but I might try one of the exhaust gas tests to further verify the issue isn't head gasket related. 

Forcing the car into limp mode seems like a good idea Ill try that when I get home today.

[89Ru]

You get heat in the cabin on warmup or is it delayed or just cold? Bubbles gurgling in the dash? Exhaust gas testing is unreliable for head gasket issues.