2008 STI Hatch: What could be the culprit?

600hpSTI · 12-02-2020, 03:35 PM

P0102- Mass Air Flow (MAF) circuit is low, and that it is not performing within its specified operating range.

P0113-Intake Air Temperature (IAT) Sensor, specifically that there is a High Input Problem with it

PO123-Throttle Position Sensor Circuit High Input

P0223-Throttle Position Sensor B Circuit Input High

P2433-Secondary Air Injection System

Okay so here's the story, 3 days ago I was driving, doing some pulls and some spirited driving (nothing out of the ordinary) and nothing was wrong, no power loss, no overheating or weird noises, no CEL, nothing. I get to my destination and when I got back to my car around 30 mins later, it wouldn't start. Rough idling and sputtering, thought it was the MAF, so I cleaned it and put it back in to no avail.

I then ordered a new one and when I put the new one in, the same thing is persisting. The strange part is that when i unplug the MAF sensor, the car starts and idles pretty much normally. I have very spotty, if any throttle response, and it sounds like the engine is backfiring in the FMIC piping. I checked the coolant reservoir and overflow and it looked like there might of been a very very thin film of oil on top of the coolant but no cream sludge on the oil dipstick or fill cap. I double and triple checked all of the hoses, lines, couplers, and connectors and couldn't find anything that looked popped off or unplugged. After the car broke down, it heated up very fast while sputtering and the coolant overflow filed 3/4. There was also a decent amount of white smoke coming from the exhaust but the car is catless and fully built.

The strangest parts are that when I unplug the MAF sensor, the car starts and idles pretty much normally. And that when the MAF is disconnected I still get a reading for MAF on my Cobb AP, but when it is plugged in the MAF reading stays solid at 14.70. SO weird.

Considering the white smoke, the small champagne bubbles forming in the coolant overflow, the overheating and sputtering, and the sweet smell of burning coolant, is likely that I blew a headgasket?

Or is it possible that the combination of all 5 CEL's all relating to the TPS/ECT/MAP connections is to blame?

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jimmy12345678 · 12-23-2020, 04:21 AM

Wouldn't hurt or be hard to check for a blown head gasket. Barring the usual signs of oil in coolant/ milky or coffee colored oil, you can rent a combustion leak tester from most parts stores.

They are very easy to use, just drain a little bit of coolant out of the radiator so the tester doesn't suck it up, start the engine and either hook up to engine vacuum or use the hand pump to pull air into the tester with the test fluid in it. It'll turn from blue to green/yellow if there's combustion gases leaking into the cooling system i.e. blown head gasket or cracked head.

12-02-2020, 03:35 PM	#1
600hpSTI Scooby Newbie Member#: 520674 Join Date: Dec 2020 Chapter/Region: SCIC Location: CA Vehicle: 2008 WRX STI Hatch Hyper Blue	2008 STI Hatch: What could be the culprit? P0102- Mass Air Flow (MAF) circuit is low, and that it is not performing within its specified operating range. P0113-Intake Air Temperature (IAT) Sensor, specifically that there is a High Input Problem with it PO123-Throttle Position Sensor Circuit High Input P0223-Throttle Position Sensor B Circuit Input High P2433-Secondary Air Injection System Okay so here's the story, 3 days ago I was driving, doing some pulls and some spirited driving (nothing out of the ordinary) and nothing was wrong, no power loss, no overheating or weird noises, no CEL, nothing. I get to my destination and when I got back to my car around 30 mins later, it wouldn't start. Rough idling and sputtering, thought it was the MAF, so I cleaned it and put it back in to no avail. I then ordered a new one and when I put the new one in, the same thing is persisting. The strange part is that when i unplug the MAF sensor, the car starts and idles pretty much normally. I have very spotty, if any throttle response, and it sounds like the engine is backfiring in the FMIC piping. I checked the coolant reservoir and overflow and it looked like there might of been a very very thin film of oil on top of the coolant but no cream sludge on the oil dipstick or fill cap. I double and triple checked all of the hoses, lines, couplers, and connectors and couldn't find anything that looked popped off or unplugged. After the car broke down, it heated up very fast while sputtering and the coolant overflow filed 3/4. There was also a decent amount of white smoke coming from the exhaust but the car is catless and fully built. The strangest parts are that when I unplug the MAF sensor, the car starts and idles pretty much normally. And that when the MAF is disconnected I still get a reading for MAF on my Cobb AP, but when it is plugged in the MAF reading stays solid at 14.70. SO weird. Considering the white smoke, the small champagne bubbles forming in the coolant overflow, the overheating and sputtering, and the sweet smell of burning coolant, is likely that I blew a headgasket? Or is it possible that the combination of all 5 CEL's all relating to the TPS/ECT/MAP connections is to blame? * Registered users of the site do not see these ads. Last edited by 600hpSTI; 12-02-2020 at 03:41 PM.

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12-23-2020, 04:21 AM	#2
jimmy12345678 Scooby Newbie Member#: 516695 Join Date: Jul 2020 Vehicle: 2008 Impreza 2.5i	Wouldn't hurt or be hard to check for a blown head gasket. Barring the usual signs of oil in coolant/ milky or coffee colored oil, you can rent a combustion leak tester from most parts stores. They are very easy to use, just drain a little bit of coolant out of the radiator so the tester doesn't suck it up, start the engine and either hook up to engine vacuum or use the hand pump to pull air into the tester with the test fluid in it. It'll turn from blue to green/yellow if there's combustion gases leaking into the cooling system i.e. blown head gasket or cracked head.