Wednesday, 15 September 2021

E30 318i: Replaced AFM (Air-Flow Meter)

I’d been messing with my AFM in order to get the car running ok when cold and when I finally fixed the massive air leak on the inlet manifold I then struggled to reset the AFM back to standard. 
In order to get the M40 to idle ok while the engine was cold I adjusted the mixture setting to run richer. Obviously this was providing enough fuel to stop the engine cutting out while the plenum was filling with as much air as the cylinders could gulp through the gap in the manifold gasket. It runs and drives ok in this setting, but idles quite high (about 1100rpm) and you can smell the stink of neat petrol out of the exhaust. Ok for short trips shunting the project car around but will need addressing to enjoy it before summer ends!
The real problem began when I had repaired the gasket, got the engine running smoothly and then tried to reset the AFM back to a stock, or near stock value. To begin with I had been putting marks and taking photos to recall where the settings were before I started messing, but you know how it is, once you get immersed into a several day long tweaking session (take that as you will!) the tendency is to get lost along the way.
I gave up trying in the end and decided the only way to dial this engine in and be sure I was not fighting with a dodgy AFM was to buy one that had not been messed with. This is in my interests anyway, as I got one from a car with far lower miles on it so the carbon-track is less worn and I know the air-temp sensor is OK too, which was a doubt with the original one.

Sunday, 5 September 2021

E46 318i Touring: Replacing leaky Oil Cooler gasket [N42]

After fixing the major oil leak from the rocker-cover gasket [THIS POST], I noticed there was still some oil pooling on the under-tray and a fews spots dripping onto the road. I traced the source up the right side of the engine (looking from the front) and could see oil filling up some cavities in the cylinder-head to the left of the oil-cooler / filter housing, so determined this to be the culprit... yes, another common one, especially if the filter-housing has been removed for previous engine work.

A replacement gasket was just £6.59 from eBay and comes as a two piece set including the main gasket that sits between the housing and the cylinder-head, as well as a smaller gasket that sits between the oil-filter housing and the coolant fed heat-exchanger. This latter one hardly ever leaks, as it's very rare to find a filter-housing that has been split apart during engine work, but it's nice to have one anyway and you may find it worth the time to replace this one while the housing is removed, though I could not see any signs of leakage so didn't bother.


1. Remove the lid to the air-con ducting that sits atop the firewall at the back of the engine by undoing the clips a quarter-turn, take out the pollen-filter and remove the weather-strip seal from the firewall.

2. Remove the air-con ducting itself by undoing the four screws using a T30-Torx socket and lifting it out.

3. Remove the rear right-side engine cover by undoing the two stud-nuts using a 10mm wrench.\

** Make sure you have a cloth / plenty of tissue to catch any oil that runs from the housing. **

4. Remove the three screws holding the oil-filter / cooler housing to the cylinder-head using a 10mm socket with a long extension bar. One is clearly visible in front of the housing, the other two being hidden down the back.

5. Lift the oil-filter / cooler housing upwards out of the head, catching any wayward oil and lift the housing clear, rotating it so as not to put too much strain on the coolant-hoses. The hoses do not need removing or any coolant draining for this job.

6. Remove the old gasket and clean both mating surfaces with a cloth and I find it always worth scraping any crud off with a razor-blade.

7. Insert the new gasket to the housing. A lug on one side sits in a notch in the housing so the gasket can only fit in one way. [If it's an older engine or the housing has been removed a few times before, it might be worth taking a belts-and-braces approach by applying some gasket sealant to the mating surface on the head, as I did with some white Corteco.]

8. Carefully place the filter/cooler housing back onto the cylinder-head, trying to spill as little oil as possible on the mating surface and reverse steps 4-1 to refit.

Monday, 30 August 2021

E46 318i Touring: Handbrake / parking-brake repair + adjustment

The handbrake (e-brake) wasn't working properly on the left side of the E46 Touring, which I assumed would either just need adjusting or at worst the spring mechanism had failed. BMWs of this era have a drum-brake mounted inside the hub of the disc-brake that is used only for the parking-brake. It turned out that the sprung stud that holds the lower brake-shoe in place had come loose, worked its way round the drum and partially jammed the mechanism, as in top picture.

The slot that the stud locks in to is part of the backing plate for the disc and it had bent outward and rounded off over time, no longer giving enough metal for the stud to hold on to. I managed to build the slot back up using a cole-chisel and there is just about enough metal left to hold the stud firmly. If it happens again in the near future then a new backing plate may be required, but this is a hub off job and a whole load more work, so lets hope it doesn't. 

Annoyingly, I had to crack open a new £13 handbrake spring assembly kit just to use the one sprung retaining stud, guess I have some spares at least. With the left side now working correctly, I gave both sides of the handbrake a quick tighten up using the rotating adjuster inside the drum.

BMW E30 - LED instrument lights flicker with rheostat switch

Work fine wired straight to power, but flicker and come on and off when run through the dimmable rheostat switch. Switching back to 5w bulbs may be the only cure.

Sunday, 29 August 2021

E30 318i M40b18: High / erratic idle issues NOW FIXED, stable at 800rpm + good throttle-response finally

After my cutting out when cold problem and no low-end throttle response from a busted lower inlet-manifold gasket (THIS POST) and high / pulsing idle issue from a poorly set throttle-stop screw (THIS POST), I have finally got the old E30 ticking over properly. It now sits at about 800rpm on idle and throttle response is smooth across the range. Pleasant.

Wednesday, 28 July 2021

E30 318i: Leaking clutch slave-cylinder... fluid low

Now the E30 is running well I took it out for a test run and noticed that all of a sudden the gears were grinding a little bit. Checked the fluid reservoir and the level had dropped to about 10mm, not good. Looked under the car and saw a spot of fluid on the drive right under the slave-cylinder. My guess, and no prizes for guessing right here, it was a leaking slave-cylinder and, hey presto... sure looks like one to me.

Replacement is ordered. I went for a cheap and cheerful one off eBay for just £16.50, though £25-40 seems to be the going rate. Be fitting this when I have chance. Looking forward to the bodywork, but mechanical jobs just keep popping up... that be old BMWs!

Monday, 26 July 2021

E30 M40 316i / 318i: Adjusting Throttle-Body and Idle Stop-Screw

Yes, this is set at the factory and they say it should never be messed with, but as the youngest M40 engined BMWs are approaching 30 years old now, chances are the stop-screw and throttle-plate will have been adjusted at some point in its life. 

Here I will explain what happens when it is adjusted, the problems it may cause if it has been and how to reset it back to stock. 


The stop-screw should have a paint mark on it from the factory to show if it has been messed with, but after so many years the mark may no longer be visible. If you feel yours has been adjusted in the past, the main reason this has been done is likely to falsely raise a low idle caused by another issue, say an induction air leak. If an over lean mixture is causing a low idle, the tendency is to tweak the idle stop-screw to get the car to tick over at higher revs and stop the engine stalling out or running lumpy. This is a great short-term workaround, but will cause other issues with the AFM / DME and fuel delivery further down the line, particularly when the underlying issue is worked out.


The issues you will get with a poorly adjusted throttle stop-screw are:

High idle.

Hunting / pulsing revs. 

Poor or no low-end throttle response.

Erratic idle (if throttle position switch TPS is not engaged).

Bogging at high revs (where wide-open throttle WOT switch is not engaged).


There is only one way the throttle can be adjusted, via the stop-screw, though the throttle-cable itself can be adjusted to change throttle response somewhat, mainly with how the pedal / cable reacts to driver input and will not affect the fuel/air ratio and the engine idle.

** The intended job of the idle stop-screw is simply to stop the throttle-plate from jamming in the throttle-body and being difficult to open when the pedal is pressed and not to change the car’s idle characteristics. BMW recommend that this is never played with, so do so at your own risk. **

1. Back off the lock-but using an 8mm wrench.

2. Use a small flat screwdriver to wind the idle stop-screw in and out. 

* Clockwise will push the throttle-linkage further from its rest position, holding the throttle-plate open slightly and allowing more air to bypass it while the pedal is not pressed.

*Anti-clockwise will allow the throttle-linkage to close further and will reduce bypass air and choke the engine while the pedal is not pressed. 


You will need a set of A/F / imperial feeler-gauges as this is how the stock throttle-plate aperture is measured. 

** If you are only adjusting the throttle-plate and do not need to adjust the throttle position switch (TPS) then the throttle-body itself does not need removing and you can skip to step 7.**

Removing the Trottle-Body:

1. Remove the main air-inlet hose from the AFM to the throttle-body by loosening the jubilee-clip and easing it off.

2. Unclip the throttle-cable from the throttle-linkage and remove the two screws holding the throttle-cable mount from the top of the throttle-body housing using a 10mm wrench. Move the cable assembly to one side.

3. Remove the two water hoses and air vacuum-hose from either side of the throttle-body by undoing the jubilee clips and teasing the hoses off with a screwdriver.

4. Remove the six nuts from the upper inlet-manifold using an 11mm wrench and the two locating screws from the manifold using a 10mm wrench. Lift the upper inlet-manifold so that the throttle body can be fully accessed. 

5. Remove the throttle-body from the inlet manifold by undoing the four nuts using a 10mm wrench.

6. Turn the throttle-body upside down and remove the throttle-position-switch (TPS) by removing the wiring connecter and undoing the two cross head screws.

7. Back off the lock-nut of the stop-screw using an 8mm wrench. 

8. Use a small flat screwdriver to adjust the throttle stop-screw by the notch in the end of it. Obviously, clockwise will move the screw further out and make the throttle-butterfly rest in a more open position. Anticlockwise will allow the butterfly to close more.

9. For the OEM setting, the throttle-butterfly should be 0.377” from the housing, so use your feeler-gauge between the side of the tube and either side of the butterfly until you find a happy medium.

10. Tighten the lock-nut up again with an 8mm wrench.

11. Now take the throttle-position switch (TPS) and locate it back in the housing so that the switch is depressed while the throttle is in the fully closed position. With the two screws loosened, the TPS can be swivelled left and right as in pic below to adjust the point at which it engages. The ideal placement for the switch is to have it click closed while the throttle is open about 1mm. (You will hear the quiet click from the TPS as it opens and closes.) When you’re happy with the TPS placement tighten the screws to lock it in place.

12. Before refitting the throttle-body, check the operation of the butterfly and TPS and make sure the butterfly is not binding to the body while fully closed as this will ruin low-end throttle response.

13. Refitting is a reversal of steps 5-1.