E30/E28: Faulty AFM (Air Flow Meter) repairs, worn carbon-track quick fix

** FOR ADJUSTING AFM AIR/FUEL RATIO SEE THIS POST **

The AFM or Air Flow Meter uses a metal flap that is opened air entering the engine to move a brass arm up and down a carbon-track. The position of the arm along the carbon track alters the electrical resistance through the circuit and this lets the ECU know how much air is coming in, so it can deliver the right amount of fuel to the injectors. The E30 uses a BOSCH AFM unit, also used in many other BMWs with Motronic or Jetronic injection systems.

The analog electrics in the BOSCH AFMs rarely ever fail, but there are two areas that are failure prone after higher mileage - a worn carbon track and a faulty air-temperature sensor.

F10 530d: 4 new Run Flat tyres (Goodyear Excellence 255/55/17)

 My run-flats that came with the F10 have been run practically, well, flat. They were an advisory on my previous MOT and the last 12 months have not been kind to them with the F seeing a fair bit of use and the two rears are about 1mm from the wear bar, so with the next test looming its time to throw some fresh rubber on.

I went for the same, like-for-like Goodyear Excellence that were fitted when I picked the car up, in 255 / 55 / 17 size. I'm not sure if these are standard fit from BMW, but it's what the police were running on it for high-speed pursuit, so they will do for me and my mainly sedate driving style...

They aren't cheap kit. Even with a discount through work I was quoted £233 for two new tyres and I needed four. This price I would consider prohibitive just for new rubber when I can get four new regular tyres for as little as £100 the lot, but the Goodyear is what I wanted so I went for used tyres. Well, they are hardly used, with the set I bought having 7mm+ of tread left and a 2019 DOT code. Three of them have a puncture repair in the tread, but even so the deal I got was too good to turn down... £250 for all four!

Run Flats or normal tyres??

I've grown used to these Goodyear tyres over the last five years, though they would not be my first choice in normal circumstances. The grip, noise and ride are all pretty good and I've had a decent run out of them given the amount of tread left when I bought the car. They have suffered two punctures during that time and this is where the Run Flats show their worth. The first I repaired straight away, but on the other occasion I ended up driving for four days and covered 75 miles on a tyre with zero PSI, yes that's ZERO air in it and to be honest the tyre still performed perfectly and there car drove as normal. OK I would NEVER recommend anyone doing this, but yes they work and are worth the extra money they cost! The downside of this convenience is the harsh, bumpy ride due to the reinforced side-walls. This may be a big factor on low-profile tyres, for instance I had 18" alloys on my E60 with Run Flats and the ride was pretty harsh, and I would imagine it gets even worse for 19" and 20" with tiny side-walls, but with my current 17 inch rims with a 55 profile side-wall the ride is actually very good, so this argument becomes negligible! 

E60: Replacing all Brake Discs and Pads.

1. Jack car, remove wheel. REAR ONLY - ensure handbrake is off.
2. Remove plastic caps and 7mm Allen-head bolts.
3. Remove caliper and hang it from the spring.
4. *On front-N/S and rear-O/S ONLY* - Remove pad wear-sensor by gently working it up out of the slot with a small flat-screwdriver. Part of the green plastic may brake off but it's very unlikely the sensor will stop working, so provided you are careful to retain the metal clip it will fit back on tight enough.
5. Remove 18mm bolts from caliper bracket and lift out of the way.
6. Remove the stud holding the disc to the hub using a 5mm Allen-key socket.
7. Wobble the brake disc off. REAR ONLY - It may need whacking from behind with a hammer as it will bind to the handbrake shoes.
8. ** If you are replacing the inboard handbrake shoes, then do this now.
9. Fit the new brake-disc to the hub. The hand-brake may need adjusting for the drum to slide over the shoes as it self-adjusts to stay against the worn drum on the old brake-disc. It will likely need adjusting to the new drum anyway. 
10. Reverse steps 5 to 1.

Pad wear-sensors are a pain to remove.

I wangled all 4 discs and pads for £140 from LVW who supply where I work. 

Belaco are a budget make, but we fit them to vans at work and they seem OK.

Mintex pads do the job.

Plenty of meat left on the old discs, but the MOT fail showed brake imbalance.

The old pads looked alright too, but no imbalance reported on the retest.