Rep Power: 0

I have a 2005 EX, manual transmission, that has run well for a long time but started having problems a few weeks ago. I'm hoping there are some ideas here so I can avoid more expensive guessing with mechanics.

A few weeks ago I noticed a decrease in power for just a minute or so while on the freeway, this happened a few times. It seemed like I had to give it a lot of gas just to barely accelerate, or even stay at 65 or 70 MPH. It wasn't always like this, just a few times. The check engine light came on, I checked the code with a bluetooth scanner and it was P0344 Cam Sensor error. Driving back from work it just about died when I was getting on the freeway, couldn't come up to 60 MPH in any reasonable amount of time, then a few minutes later started really bogging down, I pulled off the freeway, engine died. I waited a minute and it started up and drove just fine a few more miles to the shop.

The shop replaced the camshaft sensor and said there was something on the timing belt that seemed to be rubbing on the sensor I think... not too happy about that since it was about 40k ago that the timing belt was last replaced. Valve cover gasket was replaced too since it had been leaking oil quite a bit.

I got the car back and the next day I was drove onto the freeway, check engine light came back on. The code was P0420 "Catalyst System Efficiency Below Threshold" and the car felt like it was always underpowered, not just occasionally like before. So back to the shop.

The mechanic said one of the cylinders was misfiring, they traced it to a bad coil and/or spark plug, recommended changing them. (They may have said there was more than one cylinder that was misfiring/randomly firing, it's been over a week and I thought that was behind me). They also said the catalytic converter wasn't running efficiently and suggested replacing it - the inlet temperature was hotter than the outlet temperature after it warmed up. Though after talking with them they did say just replacing the coils and plugs would probably get it going most of the way.

So, I passed on those repairs since the cost of that plus the previous repairs would have put me at well over the price of that car (at least pre-pandemic prices, plus there were a few small things like an engine mount that were also fixed the first go around). I replaced the plugs and coil packs myself a few days ago. The engine seems to run better when starting up (just based on the sound idling, who knows, that's pretty subjective to me) but the engine has the same problem with power. I barely could get up to 65, let alone 70, while driving on the freeway. I did notice when I got up to 3500-4000 rpm while driving I could hear something around the engine, a little bit like unmuffled exhaust; I don't really know how to explain it. And I got another light, P2A00 "O2 Sensor Circuit Range".

Any thoughts on what could get more power (and better gas mileage I'm sure, though it'll be a while till I see what I'm getting) back into this car? I'm not opposed to replacing the catalytic converter. But even doing it myself - pretty sure that's doable - is ~$700 in parts I think. The one thing I haven't looked into is maybe just the O2 sensors need replacing, still expensive but less so. I'd just like to avoid more expensive guesses that don't work. I do have to pass state emissions soon, next month I think, so if something is really off I guess I may be forced to replace the catalytic converter.

well that's much longer than I expected, but any help is much appreciated. Thanks, Daniel

 
Rep Power: 125

Check your exhaust manifold for cracks, and see if the bolts have backed out any. There's a cat in there that could cause one of the codes, and cracks/leaks will make more noise.

 
Rep Power: 222

And you better hope they used OEM sensors