OK: today's mission is to diagnose and fix my car of one clear fault and two worrying signs.
Symptoms:
- Some white smoke (?) at low revs, not at startup, gone when the engine has warmed up.
- Low coolant levels when I received it.
- Engine light, with fatal error code P010F - Mass airflow sensor A/B correlation.
- Some slightly weak performance climbing hills in low gears, though it seems to shift on the flat. Hard to tell, as I haven't had the car long enough to tell what is normal.
- Tendency to stall more easily than it should.
So, 'head gasket' was definitely on my mind. The MAF fault gave another possible explanation though. I connected to
multiecuscan, and looked at the parameters. What stood out was an air demand of 710 whatevers, and a supply about half that, scaling with revs.
1. First things first, got it into the barn and up on jacks. Belt and braces: handbrake on, car in gear, axel stands, a scissor jack and a hydraulic jack all holding it up. Give it a good shake to see if it moves at all. Nope: it's not going to crush my head. Good.
2. Take off the engine undertray/skid plate. This step is in the repair manual, but it's not actually necessary, it just gives you easier access. Still, I wanted to have a look as I haven't properly inspected the engine before. All the bolts are mismatched, some are screws, some are cable ties, and one bolt is stripped bare but the plastic around it is completely mashed from someone's attempts to get it out. Never mind, it still keeps water out and doesn't rattle. Because the back two bolts are replaced by cable ties. I can just leave it hanging rather than take it completely off.
3. The MAF sensor is on the front left. Disconnect the battery negative, then the MAF's cable connector: use a screwdriver to lever up the yellow clip, then pinch in the black part it was tucked into, and wiggle it loose. Don't pull it by the cables! It's on hard and in a tight spot, so not easy.
4.Having a look underneath, I find out two important things: one, look! A coolant leak! It looks minor, and gives an explanation other than head gasket failure for the low coolant levels. The second point is that one of the retaining clips on the air box is rusted to s*** and wasn't fastened, allowing debris to get into the air system around the filter. This is looking promising.
5. From the top, loosen the jubilee clip that holds the air intake hose onto the MAF, then loosen the hose.
6. Undo the two bolts. This is really tight, so I used a tiny ratchet to break them loose, then a u-joint adaptor on a long 10mm socket to undo it. The adaptor gave a bit more leverage than just fingers would.
7. Work the MAF loose and take it out. Great news! It's covered in s***! That means it probably is the root of the problem, and it's not a faulty sensor. The MAF is a mesh of wire whose resistance decreases as airflow cools it, so being covered in mank and dust would make the ECU get the fuel mix wrong. I used a whole can of EGR cleaner (you need a spray that is intended for cleaning electronics and leaves no residue). For bigger bits, grass seeds and leaf fragments, I used a cocktail stick to poke it loose, and blasted it out with the spray, agains the usual flow direction. Be careful not to damage the mesh.
8. Waited for it to dry completely, and took the opportunity to change the air filter. This is really difficult unless the MAF is off, because that whole assembly pushes on the air box lid, stopping it from opening. Make sure the rubber gasket is oriented the same way (rubber to the right of the car, foam to the left). Fixed the rusty clip, reattached everything (new bolts where possible for the undertray, wire-brushed, rust-treated and re-tapped everything that needed it) and dropped it back down.
Success! Cleared engine code did not reappear, and
multiecuscan reported air demand and supply as both being about 400 at idle, and remaining pretty much in step right up to redline. No smoke of any colour. Ran out of time, but can't wait to take her out for a drive and see if it's found a bit of its missing power!