High revs when starting, causing unwanted cruise control

[pmansson]

On one of my coupes, the engine runs too fast when started cold. It immediately reaches 1500-1600 RPM, and wants to stay there when I drive off on first and then second gear. I need to use the brake to control the speed. Once warm, it reverts to the usual 1,000 RPM with no "cruise control" syndome. I pulled the "startvalve" contact (item # 9 on the D-Jetronic layout, but this changed nothing. Perhaps the cold start relay (item # 24 isn´t working correctly)?
Anybody else had this happening?

 

[Tierfreund]

Check your secondary air valve (sorry the name might be different, I only know it by it´s german name: the "Zusatzluftschieber").
It´s a valve that through a sperate metallic air filter (looks like one of those small cans of coca cola you used to get on airplanes), is supposed to give you addintional air, raising the idle speed when cold (much like a choke on a carb car). It´s inner workings are similar to a thermostat: A spring, some wax and a thermo elements. It is kept in check by the coolant running through the secondary pipe which is why it is mounted down there at the secondary pipe runing below your intake runners. (Follow the pipes and the cables (the coolant temp sensor of the d-jet goes there as well)
The air it draws is lead through a hose right up to the top of your engine, ending at the intake collector.
Try sqeezing that hose shut and see what happens.

I once had an E3 3.0Si with similar racing. After changing the valve ($$$) to no avail, I found out that corrosion in the coolant pipes (specifically in the secondary pipe) had led to a blocking of the fine passage that feed the void where the valve should have been subjected to warm coolant). So the valve never got really warm and was allways (at least slightly) open. That can really mess up all attempts of setting idle and mixture of the d-Jet.

 

[pmansson]

Thank you Tierfreund. Again somebody with extensive knowledge AND prepared to share this with all of us.
I squeezed the hose, and sure enough the revs returned to more normal 1,000 RPM. What does this prove? FaultyZusatzluftscheiber or as you experienced, corrosion in the cooland pipes? (which I couldn´t find unless you mean the thinner rubber hoses (pipes?)?

 

[Malc]

Sounds like the cold start air valve, sometimes know as air slide is sticking open, rather than closing all the way when warm.
It works on the same principle as the coolant thermostat. the BMW 2002 Tii has something similiar.
The two little hose provide a passage for the coolant.
Tierfreund is correct about it possibly getting blocked, especially if you haven't changed the antifreeze recently, have very hard water or a combination of both.
It is possible to take the valve off and check that it works by dribbling hot water through the passage, plus checking that the passage is clear.
If possible run 50/50 water antifreeze to keep the corrosion to a minimum
Malc

 

[Tierfreund]

You can check the secondary air control valve by taking it of the engine (you´ll have to drain the coolant first), and then heating it in a kettle of hot water. If it closes completely it´s ok and you´ll have to check the housing and the pipes leading to it. If it doesn´t close completely, it´s busted. They are available though not cheap (I remeber paying about 110 Euros for one). Checking it is similar to checking a thermostat.

If the valve is ok and the coolant flow towards itis blocked, you are in for a bit of work.
To get mine fixed, I had to drain all coolant, take the secondary coolant pipe (under the intake runners) out, dimantle the housing for the valve, clean and bore out everthing etc. etc. I took the oppportunity to take all external water plumnig apart and replace all and really all hoses at the time (you know it´s allways the little, hard to reach ones that blow right after you´ve changed all the others), changed the water pump, thermos and flushed the system a cuple of times. I came to that after I took a look down the secondary pipe and saw all that corrosion that blocked among other things the entry to the secondary valve.
As usual, a small problem lead to a big job. And after I´d spent a weekend in the garage, I had a fine running engine, great heating (a first) and rock stady temp gauge. But still was left wondering: If thats what the secondary looked like, how will all the little coolant lines inside the engine look?)
Leaves me glad, I no longer own that car

So frankly you should be hoping, your valve is stuck / broken. The alternative is worse. If it is stuck, before spending lots, try to free it with some WD-40 or similar.

No. 8 in this picture is the secondary pipe I was talking about

http://www.realoem.com/bmw/showparts.do?model=7031&mospid=47808&btnr=11_2457&hg=17&fg=05

No 14 is the valve, no 3 is the housing throgh which the coolant flows heating the valve where on my car the entries and exits were blocked, no 12 is the air filter for the valve

http://www.realoem.com/bmw/showparts.do?model=7031&mospid=47808&btnr=11_2456&hg=17&fg=05

 

[pmansson]

Thanks again Tierfreund and Malc. I now know exactly what to do.
Some new hoses might be appropriate while embarking on this project. I see that the return pipe (item 8) is available new. Perhaps easier than clearing the old one. I think that I will buy the air slide valve anyway, just to know that I can reassemble the same day and not have the car in parts for a week. The cheap air filter deserves renewal after 35 years. And the housing is probably not very nice inside.

I realize how tight it is down there. Some special tools and my small hands will come in handy. (A bit like attaching the overriders on the rear (Euro) bumpers).

 

[Tierfreund]

While youre ordering: Get new gaskets for the valve and the houseing. They´re cheap. And the old ones probably won´t survive beeing taken apart. And when you get a leakage down there, you´ll never notice cause it´s only a trickle. But you´ll forever be wondering why your coolant level is sinking.
If you can´t get them, you can make your own. They are simple paper gaskets.

 

[pmansson]

Thank you Tierfreund and Malc.
I finally got around to changing the air control valve which was completely stuck. Replaced the air filter too, and the gaskets of course.
The secondary pipe was fine, so I saved the new one for another car perhaps. I will now check these parts in my other cars.

 

[DustyM]

I have a similar problem with my CSi.

When you start the car it idles at around 1700rpm However if I cover the intake to the auxillary air valve this drops to around 900 but still idles well.

Once the engine is completely up to temp the idle is around the 700 mark and all is well and no air is being taken in by the valve. so it would seem that the valve is not jammed

My issue is that the valve seems to be open much more than it needs to be when the engine is cold and takes a long while to close.

The valve is new

The water ways to it are not blocked (almost as soon as the car is started you can feel the jacket behind the valve start to warm up.)

How do other CSi cars behave?
Is this valve adjustable in any way?

Any ideas?

Cheers
Jon

 

[Tierfreund]

The valve is not adjustable in any way.

And it is only regulated by water temp (on the D-jet that is, later valves on the L-Jet for example are heated by water and electrically)

As for behaviour: A completely trouble free M30 D-Jet engine will behave much like a modern FI engine. Start at first crank hot and cold without the need for any throttle action.
Idle speed about 1000 at most when starting from cold. Down to about 900 for normal, warm, running.

You might have some issue with a vacuum leak in the area of the secondary air thingy and its hose to the intace manifold. Now normally that would give you high idle at all times but maybe it´s a leak the only appears when cold. (Not very likely but worth seeing into)

OR: your D-Jet might be getting faulty water or air temperature information (there are sensors for both). One of those sensors may give no or false or sometimes false information. That may give running problems only under certain conditions...

There are temperature/resistance curves in the blue books for both sensors and they are easy to check with simple instruments.

Or: your cold start valve may be leaking or running too long beeing faulty or its relay beeing faulty thus enriching your mixture for too long after cold start (it should actually be only active for a single squirt while starting. Easy to check: Pull the electrical cable to it before a cold start (you´ll have to give the engine some throttle to start instead) and see if it idles correctly with the cold start valve disconnected. Then it would be the relay giveing a too long action. If that doesn´t work, pull the fuel hose to it and block the hose (very well, FI fuel pressure 30 psi !). If that does the trick, the valve is leaking.

Plenty more possible faults... Ah, the joys of FI....

 

[Tierfreund]

Come to think of it: If I´d have to bet: It´s still the water ways to the valve!

If the jacket behind the valve warms up quickly after engine start, that only means that water is getting close to the valve. But it needs to FLOW around the valve and not just trickle for the valve to work correctly.

I´d take the valve out an take the caseing it sits on apart. The water ways really are small to start with and are very easily blocked by even small debris.

The jacket will quickly feel warm by engine heat alone after engine start. And engine heat will be sufficient to close the valve if the engine is really at operationg temp

The symptoms you are having are most likely blocked water passages.

Try this for diagnosis: On a cool day try to drive as steady and fast as you can for at least 30 minutes. Highway, no city traffic. Something like 30 minutes at 80mph without slowing. 100mph would be even better.
Without seriously slowing down before, unclutch and pull over. If your idle is then higher (more than 1100) than it normally would be at operating temp, check wether the idle drops if you block the hose coming from the valve and going to the intake manifold.

What happens during this procedure is that driving fast gives you enough air flow in the engine compartment to cool down and open the valve.
That would mean that in slower driving it is only closed by radiant heat from the engine instead of the coolant as it is supposed to be.

If all is well, the valve would be closed at all times when the water temp is up and the test would not give you higher idle rev.

 

[DustyM]

Thanks for you comprehensive replies Tierfreund.

I don't think there are other air leaks since if i cover the inlet to the air valve with the palm of my hand the idle drops straight down to around 900.

I have already removed the valve and the block it mounts to and cleaned out all the gunk and entry and exit pipes so i'm fairly sure the water ways are OK.

I will try disconnecting the enrichment unit and start it like that.

Will keep you updated.

Would be great to get it sorted as its the only fault the engine has.

Cheers
Jon

 

[pmansson]

With the valve, waterways, filter etc in good working order; what should the RPM be when starting the car with a cold engine??

 

[pmansson]

Same problem on another car

OK, so the normal idle for a CSi when cold should be about 1100 RPM, dropping to 900 when warm. Got that on the car causing me to start the thread 2 years ago.

I now have the same symptom on another CSi with a rebuilt head and with new auxiliaries incl the secondary air valve with its housing, piping and tubing and sensors....The air valve works. I have checked that.

It starts fine but immediately goes to 17-1800 RPM. When I drive off, I will need to use the brake to slow it down on first and second. It later settles at just over 1000.

Any suggestions ???