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. 

WHY HAS IT BEEN ADJUSTED?

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.

SYMPTOMS:

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).

ADJUSTING:

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. 

STOCK SETTING:

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.

Modify BMW USB-OBD Cable for 2005 and Later Cars

If you have an older USB-OBD diagnostic cable that works with BMWs up to 2005 [DIS v44 etc.] then it will need modifying to use with later cars and version of DIS / INPA etc. The process it pretty easy.

1. Remove the four screws from the OBD section of the cable using a crosshead-screwdriver.

2. The case will likely be glued together, so pry it open with a flat-screwdriver and remove the circuit-board.

3. Locate pins 7 and 8 on the back of the OBD-plug itself, which you will find bridged by a blob of solder. [Usually the right-side two pins looking at the face of the board with the LED on.]

4. Use a soldering iron to melt the solder between the two pins so they are no longer linked. [A solder-sucking device is useful here, but it can be pulled off onto the soldering-iron quite easily.]

5. Re-assemble circuit-board in casing and replace screws.

The cable will now work 2005 and later BMW cars, including newer models for all diagnostics using this interface, inc. DIS v55, v57, INPA 6.4.3 etc.

The cable will no longer work with BMWs made before 2005 and DIS v44, so it might be worth getting a spare cable to de-solder. The ideal solution is to solder small wires to each pin that run off to a switch mounted in the edge of the casing. cn555ic has done a very good guide on how to do this on E90post.com - https://www.e90post.com/forums/showthread.php?t=672940.

F10: Centre-console / Arm-rest / iDrive-panel Replacement

The centre ash-tray had been replaced with an aluminium plate for the Police-light switches and stuff, so that needed replacing. The centre-console itself, apart from being black vinyl, which would never do, had holes drilled both sides to mount the Police radio / scanner. There was also blobs of glue all down one side, so after a brief attempt at titivating the damage, I decided a whole new one would be necessary and gave a welcome change up to a leather arm-rest!

E60 Driver's Door: No power to windows, mirrors, remote-lock, etc. - Door Module fuse.

Symptoms:

• Driver's window switch-panel doesn't operate or illuminate buttons.
• Remote door-lock doesn't operate, but all doors operate when key is turned.
• Driver's door courtesy light does not illuminate.
• Mirror control and other door switches do not operate or illuminate.
• Speaker still works.

Cause:

FUSE 10 - 30A - [Driver's Seat Adjustment] It's the first green fuse from the left in the glove compartment fuse-box.

The fuse is labelled Driver's Seat Adjustment, but is really just power from Terminal 30, which also supplies the Driver's Door Module. This module is located inside the driver's door and metes out power to the different door components so that all operations are communicated back to the CAS [Comfort Access System]. This means that when the fuse to the door module blows, power is lost to the window, mirror, etc. switch panel, the remote door lock, basically everything except the speaker. This causes a lot of confusion as to the root of the problem, as it would be very hard to guess that the fuse for the driver's seat adjustment motors would also power a hidden module in the door that controls everything. Oh well, that's modern cars. 

There is a lot of conflicting information on forums about this. It appears that most people have the symptoms described above and not one reply mentions this fuse! Owner's have even shelled out for new door modules which have had no effect and perhaps their lack of further contribution to the thread suggest the same sheepish frustration I felt when I found the fuse. Quite a few people have foxed indy auto-electricians with this problem, who have probably been testing wires, as I did, while not knowing about the fuse.

I eventually discovered the fuse by tracing the wiring diagrams on bmw-planet.com. This is a brilliant place to access the TIS wiring-diagrams and navigate them easily. I have condensed the layout of the door module wiring in the pic below.

E60 Audio: Fitting an On/Off Switch for the Amp/Subs.

Even though my amp and subs turn off with the ignition I like to have a separate switch somewhere so they can be turned off manually when I don't want them on.

I fitted it at the back of the coin-tray in the centre of the dash so it's invisible and causes the least damage to the fascia, plus I plan to fit an aux. in there at some point too. This also keeps the extra-wiring needed to a minimum - I just snipped the remote-wire coming from the cigar-lighter and connected it to the back of the switch with two female-spade crimp-connectors.

I did this while the trim and fascia were removed during the remote-wire fitting in THIS POST.

E39 Audio: On/Off Switch for the Amp/Subs

The system remote shuts off with the ignition [see: Getting a Remote Signal for the Amp], so I've no worry about getting a flat battery, but it would be nice to have a manual On/Off switch inside the cabin so I can mute the subs while driving if I need to, without having to cut out the rest of the speakers.

While I had the back seats out I ran a wire through the bulkhead into the o/s rear footwell [see: Adding an On/Off Switch], so I got hold of a beacon-switch from a tipper at work to fit inside the cabin. The plan was to run the wires out from the middle of the seat and under the carpet on the transmission-tunnel, then fit the switch inside the armrest-compartment. Neither of these panned out. Running the wires under the carpet is doable, but to lift the carpet [and the sponge backing] up enough involves completely removing the armrest console, as well as all the side trim and clips, so I've taken a shortcut for now and run the wires under the trim below the o/s door, then under the driver's seat and through a gap in the side of the console. The wires are exposed, but they're well hidden and I've made sure to keep them well away from the seat-runners.

As for the placement of the switch, which is over an inch deep with the wire terminals on, it turns out there's just no room for it inside the centre-console. The base of the armrest-console is a solid steel tray with an electronics-module right under it and the storage-tray below the armrest angles up to fit flush with it too. I don't want to go further forward on the dash and mess up the wood so I've fitted it in the storage-slot under the rear air-vents. The plastic slot was missing anyway and the vents were hanging loose, so at least it looks complete now even if it's a pain to reach. Not a problem for people in the back though and that might not be such a bad thing if one is screaming we've missed our turn-off and we can't hear over the drum and bass. I just used a piece of thin plywood for the panel, covered in the leftover vinyl wrap from my ScoobyLab stickers. It's a bit shiny, but the vinyl gives it more of a trim look than black paint.

E39 530d: New Drivers Window Switch

Re: my post last week - 'Gotta have a teething problem - Drivers Windows Switch', the problem is now resolved, thanks to a whole new switch module. Well a used one, but advertised as "perfect condition" by nerijusnerka on eBay and it lives up to the hype thankfully, seeing as the unit was a little pricey @ £25 delivered, but not bank-breaking to have my driver's window back in action.

It's a piece of cake to get the old unit out and plug in the new one and as soon I tried the switch all functionality had returned - I tested each window and the child locks, all now working fine, so I'm glad my deduction was right and it's not the computer... I also noticed a chip on the edge of the broken unit where someone has obviously had a go at fixing it before, so it's nice to give the car a blemish-free interior again - I can't spot a single other mark in there!

PROCESS:

1. Fold a cloth over the end of a flat-screwdriver and gently prize it down under the edge of the switch-panel. Lift the edge of the panel up with the screwdriver a few millimeters and continue around the panel until it is proud enough to be lifted out by hand.

2. Starting with the rear one, unplug the two slim upper clips from the panel by depressing the button in the centre until the latch can be lowered. Lowering the latch completely lifts the plug clear of its socket.

3. Slide a flat-screwdriver down the gap on the rear-face of the large lower clip and lever the base of the clip outwards about 1cm until the wiring-clip slides freely out of the socket.

4. Reverse the process to install the new switch-panel.

E39 530d: Gotta have a teething problem - Drivers Windows Switch

The car has been better than good so far. It drives superbly, is quiet and refined, swift and economical - the 3.0 litre diesel engine is incredible, managing 184bhp and still getting me comfortably over 40mpg for my work runs! A far cry from topping up the Scooby tank by at least £40 every week, but not a world away from the horse-power... go figure.

The only fault I have to report though is a faulty driver's window switch unit. It worked fine for the first few days, then became sporadic and finally stopped working altogether. I tried it on my way home from work this evening and to my surprise it went down. Unfortunately it wouldn't come up again so I was forced to figure the problem out tonight. I drove around for a while in the hope that it would reactivate, but the window didn't budge an inch. I used up half a roll of black-tape sticking a bag over the open window on the windiest night of the year, only to then discover that the windows can operated from the remote key-fob. A genius feature of the techy BMW is that holding down the lock button will close any open windows and turn any electrics off. Holding the boot-release button causes all four windows to go down. I am impressed and very relieved!

The likely culprit was the switch-unit, but I prized it off to find 3 separate wiring harnesses leading to it - one each for the front 2 windows, rear 2 windows and the rear child-lock, so I became worried that the problem was elsewhere is the electronics system. The door-hinge wiring harness was a possibility - apparently they're prone to splitting and getting corroded - or worse still the car's brain - the GM5 computer, which controls the ABS, door-locks, windows, air-con, basically every electronic gadget and these are pricey to replace.

Luckily though, the drivers window responded immediately to the key-fob trick so the GM5 is sending/receiving signals just fine and the door-hinge wiring is still sound. Phew, this means it can only be the window switch-unit - when one circuit in it breaks it must kill all the buttons, regardless of which loom they plug into.

I've found a load of E39 switch-units on eBay around the £25-40 mark so I'll have to get one when I can and see if that puts the window problem to bed. It'll have to wait now though, as my new Angel Eye headlights have just arrived. Get in.