Lots of codes and misfire/lean issues

Hey guys, having misfire/lean issues with a new to me 2003 CRV EX awd auto with 245k miles. It’s in great condition for its age and has a lot of parts brand new as of the last couple thousand miles, but having some issues and hoping someone might be able to guide me to the next step.

Drove fine when I bought it and passed emissions test in California. About a week after I took it to get an alignment and it threw a P0171 code for lean fuel mixture on the way home and searched that this is typically caused by vacuum leaks and though maybe they just knocked a hose loose. After weeks of searching I have yet to find any, but in the meantime I have now got new codes popping on and off P0303 misfire, P0304 misfire, and P0505 idle air control system. It seemed that all these codes also could go along with a vacuum leak but to be proactive I checked plugs a coils and adjusted the valves which were a tad off. The plugs and coils which were replaced by the previous owner had oil on them so I also replaced the valve cover gasket which the previous owner said was new as well as the idle air sensor and injectors, and it got me thinking he was perhaps chasing the same issue so I did a compression test and got roughly 190-190-170-170 which concerned me a little bit, but it’s not horrible and the car at times drives fine sometimes.

The live data on my scanner shows that the short term and long term fuel trims are hanging out between 15-30% so definitely lean and compensating for an issue. What I’ve noticed is when the engine is cold high rpm’s will increase the positive trim, but when the engine is at operating temperature higher rpm’s will decrease the trim percentage.

Any suggestions would be greatly appreciated! Adrian

after market coils go bad you didn't say if you tested o2 sensors or air in exhaust system . good luck

Thanks so much for the reply. So I got a box of old parts from the previous owner including 3 used sets of coils (2 sets were OE densos) on top of a set of Densos on the crv. I tried swapping around coils and it didn’t change the problem but it did get me thinking that he was chasing the same problem previously.

I thought I movies the front O2 sensor wasn’t oscillating correctly and replaced it with a denso and it made no changes either. And I have yet to completely check the exhaust for a leak but there was no obvious issues.

Based on the slight discoloration of your plug, I'd guess your K24 is burning oil. Not unusual at that mileage, and probably not related to your lean condition.

Since you've already started looking at fuel trims, let's stay with that. You noted the total trims get better with engine speed with the engine warm, correct? That'd suggest a vacuum leak, and may also explain the P0505. Watch your trims again with the engine warm at idle, 1,500, 2,500 and 3,500 RPM. We're looking for total trims (short + long), and seeing if there's a trend with engine speed.

If you confirm the total trims get better with engine speed, go down the vacuum leak path. Start with the good ol' ScannerDanner water bottle method. Any time you hear the water getting sucked in, you've found a leak.

Don't overlook the motor mount solenoid near the end of the fuel rail. It regulates manifold vacuum to the front motor mount. Super easy to knock a hose off, or just have a failed mount. Cap or pinch off the solenoid hoses where possible and recheck your trims.

Thanks so much for that response. Yes when the engine is warm the trims go down with increased engine speed.

I’ll keep tracing what seems like a possible vacuum leak! I tried brake cleaner but did it carefully on a cold engine, I’ll try a water bottle instead, and perhaps finding a way to build a smoke machine.

Can you elaborate on the motor mount solenoid, is that a typo?

Thanks!

Also just noticed while watching live data while actually driving under load at operating temps that the more throttle I give it that the trims go up!

So they go up with revs on a cold engine, go down with revs on a warm engine, but then switch back up to going up under load/throttle/wot.

Any thoughts?

Update and still no fix.

I bought a smoke tester and pumped smoke into the intake with the throttle open and also the exhaust pipe just in case there are any pre O2 sensor leaks and unfortunately found nothing. About the only thing that hasn’t been tested or replaced yet is the pcm and fuel pump. So since the fuel pump is super easy to get to on these crvs I went ahead and replaced it. Unfortunately the
trims shot up right away and got back all the codes. One thing I did notice is the car did accelerate less sluggish and with rpm revs the trims do go almost all the way to zero which wasn’t quite happening before.

Any other suggestions guys?

Update. Swapped the salvaged throttle body/IACV and no change. I noticed a small exhaust leak at the manifold and thought I had found my issue as after I replaced the gasket, the trims immediately looked better and the car drove better. But the next time I started it went right back. So since I tried everything I bought a block tester and it looks like the head gasket is failing. I just wanted to update the post for future viewers.

looks like the two adjacent cylinders with lower compression numbers are the culprit, and I’m sure the previous owner found this out too and passed along the headache.