2014 Chevy Malibu: P0171

[kevm14]

System too lean.

Yeah I agree. Put a load on it in gear and LTFT came down to 10 at least so definitely worse under vacuum. So probably a vacuum leak.

https://www.youtube.com/watch?v=QrO5k6a ... hristensen

Evidently the most common issue is the intake manifold bolts loosen up. However, this comment caught my eye:

I'm a heavy equipment diesel technician so this issue is never common place but own a 14 2.5 malibu. Had same issue twice now. Did some research to find this issue. Then one day at work met a guy who's uncle designed the 2.5 and 2.4 eco motors for gm. Me and him had a great talk let me tell you. The only way to resolve this problem it to remove the rubber gasket from factory and install a neoprene gasket. The rubber creates vibration and bolt will lossen up again. Since I did it's never lossened up again. The 2.5 pcvs need changed often. Don't forget to do that. You can blow a rear main seal. No good. The pipe that connects them has a downward loop which collects moisture. I haven't done this next step yet but will because it makes complete sense and the guy told me do this and I fully believe him. The pipes loop needs removed and install and straight hose with two shrink clamps on the ends. No more moisture build up. He's seen many many rear main seals blow because of this. " ". Ok ladies and gentlemen good luck.

So the current plan:
- Look up torque and tightening sequence
- Tighten bolts (what is this, a Northstar?)

If it happens again I'll look into the neoprene gasket. His comment about the PCV also sounds like something I might want to do before something bad happens.

PCV info: https://www.youtube.com/watch?v=LYyMJA0 ... ovanFoster

I'll order both.

[kevm14]

Torque sequence info.
https://www.chevymalibuforum.com/thread ... ecs.69945/

[kevm14]

That was it. Like 4 of the 6 bolts were very loose.

With transverse 4 cylinders there are two layouts: exhaust in the front and exhaust in the back. This car is exhaust in the front so intake is in the back. I was envisioning something more accessible. Getting access to them was trickier than I expected basically.

First I had to remove the engine cover which requires removing the oil fill and three torx bolts. Then the intake resonator sits right on top of the intake. Removing it is somewhat involved, oddly. From memory:
- Loosen the tube clamp to the throttle body. Sounds easy but it's buried. Had to do the old reach around with a 5/16" socket and there was no room to swing the ratchet. I got it loose.
- Some evap tube is clipped in on top
- Two Christmas tree fasteners hold some tubes around the back which are hard to access (easier if you do them last and get the resonator somewhat up out of its spot first)
- One 10mm bolt
- Loosen clamp from tube that goes to MAF
- The PCV system has a hard plastic tube with three ends: one goes to the intake resonator, and the other two go to both PCV valves. This was tricky until I figured out the secret handshake. It's kind of a plastic spring clamp and there's a tab you can push to relieve the tension to pull the tube off the nipples. This one also held me up for a bit while I studied it.

Once all that nonsense is disconnected you can basically just pull the resonator off by loosening from the TB (it will be somewhat stuck).

After that's out of the way, the top 5 bolts are fairly accessible using a 6" extension and 10mm socket. The intake is plastic and has molded access ports for each of the top 5 bolts. But one hole had a very large and strong acorn sitting in it. Hilarious. That took some fiddling.

ANYWAY, after all that, like I said above, 4 of the 6 total bolts were very loose. Tightened them in the sequence in the above link (just the standard center-out approach). The 6th was very difficult to locate and put a socket on. Totally blind and like around the bottom of the intake or something. It wasn't loose anyway so that's good I guess.

Did some other useful maintenance:
- Cleaned TB. It was dirty but not debilitatingly so.
- Removed MAF and sprayed a liberal amount of MAF spray through it. Didn't really seem dirty.
- Removed both PCV valves (one bolt and it's an O-ring situation). Sprayed them out with carb cleaner and air. They both rattled (they are also plastic). Reinstalled.

Road test revealed it's fixed. Trims are back in control and generally LTFTs under 10. I reset the code. The internet says this will come back until I replace the intake manifold gasket with the updated neoprene design but I want to see how long it takes to come back. If it's REALLY soon, then I'll have to bite the bullet. If it's like in 30k, then not sure why I wouldn't try tightening the bolts again.

[kevm14]

Replaced both PCVs and properly connected the other harness item to the back of the resonator.

135,308 miles.