Hey guys..I am getting my 2003 M45 back up to 100% and almost there...but there is a nagging issue. A little background...

I purchased it in 2013 and due to a variety of issues (many personal) the car was not driven much in the time since. I've only put on about 3K miles since 2013, so a lot of time the fuel became old. I replaced all fluids when I got it and changed the plugs, and cleaned the MAF but neglected to hook up the harness and started it. I immediately knew the problem and hooked it up but the check engine immediately lit up.

So we come to now. The check engine light will pop on, and usually stay on (until cleared) but sometime (like today) will turn off on it's own. Sometimes the VK will run smooth as silk and feel very responsive, but then I can feel the engine "rumble" a little and obviously not as smooth. Not horrible and the RPM's will not budge when it does this. I have done the idle reset and that will immediately lower it to the 650rpm range, but then will drift up to around 900 (the 507 code likely).

The codes that are popping up is P0308 and P0507. My friend (a mobile repair guy/tech) figured the 308 was a bad coil and/or plug. The car sat for almost a year until now, but last year at this point a code showed the #3 cylinder, but not anymore. He found the coil was good but we changed the plug anyway, but the old plug doesn't look bad at all (remember, only about 3K miles on it since 2013). All the injectors seem to be functioning (listening to them), but he thinks it may be the issue may be clogged injectors due to all that sitting, or an air leak in the exhaust manifold, and install a new gasket.

I don't want to keep throwing new parts on, as 8 new injectors are $$$, and all that work for a new gasket may not solve it. I've thought about doing a fuel rail cleaning, or removing the injectors to be bench cleaned, as well. Any thoughts on these symptoms and where I should try next? As with many of us, money is tight right now, so I want to, hopefully, zero in on a fix. Thanks guys!

You sure it isn't also an air leak in the intake tubing after the MAF? Try running a can of Seafoam or Chevron through the gas and through the intake manifold and see if that helps clean some of the gunk out.

I have been running injector cleaning the past couple tanks, but nothing as of yet. A clogged or leaky injector might be very likely as to all that stale gas that has sat in the fuel lines. It has 121K miles now, and I bought it in 2013 with around 18.5K....as you can tell, not a lot of fill ups in the past 7 years. Maybe I should take apart the intake tubing of the MAF and see if anything is loose or not fitting properly. I've never done the Seafoam through the manifold before. Difficult?

No, I have a HowTo on how to do it in the my signature. Pretty easy but you'll likely need another person such as your friend.

I'd definitely investigate the intake tubing, especially after the MAF. After all of these years, you may have a very slight tear in one of the boots and as a result it could be sucking in air post MAF, resulting in a wonky A/F.

I'm going to reexamine all the connections with the MAF and the throttle body tomorrow and see if anything jumps out. Thanks!