I will thank everyone (especially Fish - you rock!) in advance for all the information i gained on this site.
I have a 2000 Corolla with 142000. The check engine light came on a couple weeks ago - code P0107 - running lean. When I started the car, the idle moved around a bit, then settled. No idea what the RPM was as I do not have a tachometer. When I put the car in D or R, the idle dropped and the car stumbled unless I pumped the gas pedal a tad. Once I got moving a few yards, the car seemed to run fine, with little to no hesitation. I could hear what sounded like a vacuum leak coming from the intake manifold gasket region and around the throttle body. With the car in P, I opened the hood and manually opened the throttle a bit and the leak became more pronounced. I did not think it was the IAC valve as when I turned on the air conditioning, it did what it should.
Hoping to fix the situation, I did all of the following yesterday: Cleaned MAF, cleaned throttle body, changed throttle body gasket, changed intake manifold gasket, changed OCV filter and visually checked all tubes. When I started the car it stumbled until I gave it a little gas - I assume the ECU was just figuring things out. Once the car warmed up (still parked) it sounded fine. I took it for a easy drive - all seemed fine. I parked the car for an hour and then came back to start - all fine - until I needed to accelerate and the car stumbled. I backed off the gas and pumped the peddle and it recovered and took off like there was no problem. However, the CEL came on.
I still hear what seems like a vacuum leak from the intake manifold - but specifically (with use of stethoscope) from tube that comes out from the 4th cylinder. Is it possible that an o-ring from the 4th cylinder fuel injector has been the vacuum leak all along? Fuel economy has not changed anything significant during all of this. I used fuel injector cleaner before doing any of the above and still no results.
If it is the o-ring (worth changing I would guess) - does the injector just drop in and only held in place by the o-ring, thread to screw in etc?? Is it better to replace the grommet at the same time, or can I get away with just the o-ring? Am I on the right track?
Thanks in advance - first post for me here.