idosubaru Posted Wednesday at 10:12 PM Share Posted Wednesday at 10:12 PM Engine starts and idles fine, can't tell anything is wrong until you go to drive it. It's severely underpowered. Floor it and it very slowly accelerates, sometimes can get up to 40 mph on flat or downhill. It won't even make it up a steep mountain, so it's undrivable around here. New headgaskets, timing belt, and compression tested fine so I assume the timing marks are still good, but Ill check them tomorrow. Drove fine for 3-4 months after the HG then gradually got worse over a week before it became undrivable. The oil had significant coolant/water mixed in with the oil before I did the HG's - could the valve control solenoids be damaged by that? P0038 front O2 sensor code - car does the same thing with the sensor plugged in or unplugged. Will these run without a front O2 plugged in? Maybe the 02 sensor is bad. It has a 4 wire Bosch O2 sensor with the old plug spliced on - does anyone know how to verify the wires are correct? It had a cylinder 3 and multiple cylinder misfires - I replaced the plugs and wires with subaru issued goods, and the codes for those went away - but the CEL did flash last night on a test drive then quit...so maybe it's still doing it intermittently. Any suggestions..... Link to comment Share on other sites More sharing options...
brus brother Posted Wednesday at 11:12 PM Share Posted Wednesday at 11:12 PM (edited) Possibly clogged cat converter(s)? Broken bit's of the honeycomb will follow gravity and clog the exhaust when car is heading up hill. The noise will startle the neighbors but if you can disconnect the cat(s) and test drive, that will help in diagnosing this issue. Buddy had this issue and just emptied the broken bits and drove on. Edited Thursday at 12:49 AM by brus brother 1 Link to comment Share on other sites More sharing options...
ronemus Posted Thursday at 02:10 AM Share Posted Thursday at 02:10 AM I once had the same symptoms from a bad airflow sensor, and another time it was the pedal position sensor. There are lots of possibilities for those symptoms. It will run without the O2 sensor, but it does so in limp home mode which would be as you describe - I would start with a new O2 sensor. Rock Auto sells Denso Front O2 Sensor which is GTG. How is fuel mileage? If the A/F ratio is off the mileage will suffer. Link to comment Share on other sites More sharing options...
idosubaru Posted Thursday at 02:28 AM Author Share Posted Thursday at 02:28 AM 2 hours ago, brus brother said: Possibly clogged cat converter(s)? Broken bit's of the honeycomb will follow gravity and clog the exhaust when car is heading up hill. The noise will startle the neighbors but if you can disconnect the cat(s) and test drive, that will help in diagnosing this issue. Buddy had this issue and just emptied the broken bits and drove on. Oh wow my good sir, wasn't considering the exhaust at all. That would be awesome. Aye aye captain - I rammed one out of an XT6 20+ years ago. 16 minutes ago, ronemus said: I once had the same symptoms from a bad airflow sensor, and another time it was the pedal position sensor. There are lots of possibilities for those symptoms. It will run without the O2 sensor, but it does so in limp home mode which would be as you describe - I would start with a new O2 sensor. Rock Auto sells Denso Front O2 Sensor which is GTG. How is fuel mileage? If the A/F ratio is off the mileage will suffer. It's not drivable enough to accrue miles and calculate gas mileage. Yeah this is a new sensor but it's the style that comes with bare leads you splice the old connector onto - and I do'nt trust that it's wired properly. I'll check those. Link to comment Share on other sites More sharing options...
idosubaru Posted Thursday at 03:37 AM Author Share Posted Thursday at 03:37 AM Doesn't seem to be the oxygen sensor. I'll try disconnecting the exhaust in the morning. Link to comment Share on other sites More sharing options...
forester2002s Posted Thursday at 05:43 AM Share Posted Thursday at 05:43 AM Could be a partially-clogged fuel filter. Put in a new one, and see if it makes any difference. Link to comment Share on other sites More sharing options...
idosubaru Posted Thursday at 12:27 PM Author Share Posted Thursday at 12:27 PM 10 hours ago, ronemus said: I once had the same symptoms from a bad airflow sensor, and another time it was the pedal position sensor. There are lots of possibilities for those symptoms. What year/model engine and did you have check engine lights in those cases? Max 4,000 RPM with no power for hills but otherwise drives without hiccup or stalling is oddly specific, I doubt your symptoms were identical. It would be drivable on flat land, but can't get up hills. Link to comment Share on other sites More sharing options...
idosubaru Posted Thursday at 12:28 PM Author Share Posted Thursday at 12:28 PM 6 hours ago, forester2002s said: Could be a partially-clogged fuel filter. Put in a new one, and see if it makes any difference. 2005-2009 doesn't have a fuel filter, or it's "in the fuel tank". Link to comment Share on other sites More sharing options...
idosubaru Posted Thursday at 12:30 PM Author Share Posted Thursday at 12:30 PM Cat converter - seems fine, disconnected exhaust and still runs just as bad. Fuel filter is in the tank, can't replace - i'll have to pressure test or pull the fuel line and see how well is sprays out Ill get a new oxygen sensor later. Link to comment Share on other sites More sharing options...
idosubaru Posted Thursday at 01:27 PM Author Share Posted Thursday at 01:27 PM 14 hours ago, brus brother said: Possibly clogged cat converter(s)? You were right! Thanks man! Now...this newer 05-09 stuff has the curved catalytic converters right by the engine, they're going to be much harder to gut.... Link to comment Share on other sites More sharing options...
idosubaru Posted Thursday at 01:32 PM Author Share Posted Thursday at 01:32 PM 1 hour ago, idosubaru said: Cat converter - seems fine, disconnected exhaust and still runs just as bad. Converter ended up being the problem - just took a minute to warm up and relearn I guess, Runs perfect without the exhaust connected 3 Link to comment Share on other sites More sharing options...
brus brother Posted 16 hours ago Share Posted 16 hours ago On 1/8/2026 at 8:32 AM, idosubaru said: Converter ended up being the problem - just took a minute to warm up and relearn I guess, Runs perfect without the exhaust connected Runs perfect albeit on the loud side. VAROOOM!!! Link to comment Share on other sites More sharing options...
brus brother Posted 16 hours ago Share Posted 16 hours ago On 1/8/2026 at 8:27 AM, idosubaru said: You were right! Thanks man! Now...this newer 05-09 stuff has the curved catalytic converters right by the engine, they're going to be much harder to gut.... Try just banging on it and dumping out the broken bits. Link to comment Share on other sites More sharing options...
brus brother Posted 15 hours ago Share Posted 15 hours ago I just spoke with buddy and he reminded me that he used 2 vacuums. One blowing in and one sucking out the other end. Save the pieces and find a recycler. Link to comment Share on other sites More sharing options...
idosubaru Posted 12 hours ago Author Share Posted 12 hours ago 3 hours ago, brus brother said: Try just banging on it and dumping out the broken bits. Oddly I didn't get one tiny particle to come out by doing that. 3 hours ago, brus brother said: I just spoke with buddy and he reminded me that he used 2 vacuums. One blowing in and one sucking out the other end. Save the pieces and find a recycler. Interesting suggestion, doesn't seem like enough power but I'll be taking it apart again - ordered a $80 ebay exhaust manifold (if you've seen the 05+ manifold pretzels that's a crazy cheap price) to have some options. I'm wondering if the clog is in the header (i think it houses the catalysts), the mid pipe, or the mufflers or more than one. Hesitates around 5,000+ RPM's/flooring it (which is sometimes helpful on a steep mountain grade but others unecessary - but makes me thinking something is still clogged. Otherwise it drives totally normal. 4 hours ago, brus brother said: Runs perfect albeit on the loud side. VAROOOM!!! I wore ear protection but should call and apologize to the neighbor - her horses went tearing off towards her house. Link to comment Share on other sites More sharing options...
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