BMW 330iT E46

Some might remember the saga of my brother's car. It cut out one day (he said just like running out of petrol) and refused to start. Because it is
winter, said brother had his local garage look at it. (He'd normally have a go at fixing things himself first) That car is mainly used for towing their caravan. so they could make do with the other one in the meantime.
Said garage decided to do a compression check and declared the engine scrap. Rather odd as it was running just fine before, and made no odd noises when cutting out.
Car was returned to my brother with coils and plugs removed. With a long list of what their code reader said was wrong.
Brother then did the obvious thing and checked for fuel to the injectors. None. Replaced the fuel pump after checking the old one was dead, and it started after reassembling the ignition.
So on to the point of this post. It runs well - just as before - but won't idle. But starts instantly with a whiff of throttle.
It's a electronic throttle. Does anyone know the method for checking this and re-setting the idle speed? We've guessed the garage may have disturbed something when ripping it apart, as it was just fine before.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On 15/02/18 17:21, Dave Plowman (News) wrote:

Any help? This is resetting learned values, so it might do what you need?
http://www.bimmerfest.com/forums/showthread.php?t 7646
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Thanks Chris - I'll pass that on tomorrow. I'm not really familiar with this electronic throttle - it seems it also has an idle valve arrangement.
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On 16/02/2018 00:06, Dave Plowman (News) wrote:

There was a suggestion elsewhere that you need diag equipment to reset the throttle body if it's been disturbed, but I'm not familiar with the car either. That's what you need to do with some VWs (like my other half's Lupo)- it runs the stepper motor from end to end. This one is a bit odd in that it has a traditional cable throttle /and/ a stepper.
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Chris Bartram brought next idea :

The stepper is usually for the cruise control.
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It's drive by wire. The thottle is some form of stepper motor controlled by an electronic throttle pedal. So not the traditional bowden cable. I assumed it makes economic sense as it would make a cruise control that much simpler. But I also assumed it would control the idle speed at all times too - so was surprised it also seems to have some form of extra idle valve.
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Dave Plowman (News) wrote :

Usually - the (IAV) valve simply bypasses the throttle butterfly, whether stepper driven or bowden cable operated. The IAV is under direct control of the engine ECU, opening and closing rapidly. The mark space (open to closed) ratio controls the engine tickover speed. I would guess that a stepper motor system simply might not be able to react quickly enough, to be able to hold a steady tickover speed.
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It's all quite odd. My Boxster has an electronic throttle - probably very similar to the BMW one, since both Bosch engine management. But the cold fast idle on that jumps down in very noticeable steps as it warms up. The hot idle is very consistent.
On my old Rover with MegaSquirt injection, I've fitted a PCM controlled fast idle valve which reduces the fast idle very smoothly.
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After serious thinking Dave Plowman (News) wrote :

I would suggest that is absolutely normal. A cold engine will need a faster tickover, to overcome the extra drag of cold oil and engine parts. Every modern ECU controlled car I have owned, has dropped its tickover speed from cold, in distinct steps.
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My previous car, a BMW E39, with the older cable throttle didn't. It reduced the idle speed smoothly.
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On 16-Feb-18 2:59 PM, Dave Plowman (News) wrote:

Possibly like my Nissan, that has no less than 4 idle systems.
1: Base idle set to 800 rpm by a screw with the idle valve unplugged. 2: AAC, auxiliary air control. AKA idle control valve, pcm solenoid with a plunger valve. 3: FICD, Fast idle control device. Solenoid opens when air con is on. 4: Air regulator, high idle when cold. A bimetal strip rotates a shutter that slowly closes a hole. Wired in parallel with the fuel pump. Pump runs for 5 sec when ign switched on and all the time the crank angle sensor is turning.
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The old Rover had that EAV. Didn't realise it survived to CPS days. Later Rover V-8s, still with a distributor, had a stepper motor so closed loop idle.
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On 16/02/2018 10:15, Harry Bloomfield wrote:

Not here, it doesn't have cruise. The stepper can vary idle speed, and indeed throttle opening as well as the physical cable. It mostly seems to get used to alter idle according to load and temperature. If the adaption gets out of whack the idle pulses up and down when cold.
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Dave Plowman (News) used his keyboard to write :

I would be looking at that idle valve maybe sticking, or an intake air leak.
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Right - that has been tried, but no actual success.
If you keep the engine running from cold by blipping the throttle etc, it does eventually idle on its own when warm/hot. But at a slightly lower speed than previously.
Neither Haynes or the copy of the TIS I have here mention a cold idle valve. Nor is one for sale on Ebay listed for this actual model.
So it rather looks like the fast idle is done by the electronic throttle body. Which would make sense to me. The car can now be driven, and apart from this drives normally. So much for it needing a new engine. ;-) But just why the throttle should work normally when driving, but not go to the cold fast idle position is the $64,000 question.
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Duff temperature sensor somewhere? The engine management computer just doesn’t know that the engine’s cold? Maybe you’ve covered this. Just a thought...
Tim
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In article

I'd don't know this engine management intimately. but the coolant sensor usually also sets the fuelling for a cold start (rather like pulling the choke) And that appears to be OK since it starts readily enough in this cold weather.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Is mixture enrichment for cold engines as important with fuel injection systems? You don’t have the same degree of problem of fuel hitting cold manifold and weakening the mixture before it reaches the cylinder.
Just wondering if an injected engine would start pretty well without enrichment.
Tim
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On 21-Feb-18 6:41 AM, Tim+ wrote:

They still need a rich mixture to start.
Need an even more rich mixture for hot start. My car has a solenoid on the FPR vac line, disconnects from manifold and connects to atmosphere for 3 min during hot start. As the FPR sees about 8-10psi higher pressure it delivers (14.7+8)/14.7 more fuel. What it actually does is flood the engine so most people unplug it.
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Not quite so - but you do need a richer mixture for a hot start and for a short time afterwards.

A problem with many cars is heat soak when you park with a hot engine and on a hot day. Which can make a big difference to the temperature of the inlet tract etc over a running engine with draws in ambient air, if you attempt a hot start soon afterwards. You may also get a degree of fuel evaporation is the fuel rails. One way round this can be to increase the fuel pressure for a hot start. On my MegaSquirt equipped engine, I also open the fast idle valve setting for hot cranking. As soon as it fires, it goes back to normal. That does seem to suggest I'm giving it too rich a mixture for a hot re-start, but since it works I've left it like that. The big problem with this sort of tuning is getting the conditions exactly the same each time before changing anything - to avoid chasing your tail. ;-)
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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