Idle dropping when coming to a stop.

[turboe36]

Hi all, I'm running a 3-wire bosch idle valve on my E36 M3 with an SM4 1.07 box. It idles decently, sometimes hunts around a bit especially when warming up. But the main problem is, when I'm coming to a stop the idle will fall very low and occasionally stall, then come back up to a nice 800 rpm idle. What setting would help this in the IAC tune?

Thanks in advance!

[Chris]

What size/type injectors in that engine ? Does it do the same if you rev it a bit and snap the throttle closed ?

Chris

[turboe36]

Siemens Deka 60# and yes it will drop low if you rev and snap the throttle closed.

[Chris]

If you can please post a copy of your cal file. If you would prefer you can email it to me. Please advise.

Chris

[turboe36]

Here it is. Thank you Chris!

http://www.smeraglinolo.com/private/NEW01.CAL

[gti]

In your cal file, IAC is set to Bosch 2 wire, not 3 wire.
I would also try to increase ignition advance immediately below your normal idle speed.

[Chris]

Does that engine have individual throttle per cylinder or a single throttle and plenum setup ?

Chris

[turboe36]

In your cal file, IAC is set to Bosch 2 wire, not 3 wire.
I would also try to increase ignition advance immediately below your normal idle speed.

There is no 3-wire. You run 2 wire and configure two outputs for the IAC out, with one inverted which balances the signal. Will try the ignition advance though.

Does that engine have individual throttle per cylinder or a single throttle and plenum setup ?

Chris

Chris, it has a single throttle body with a traditional intake manifold.

It is running delta idle ign at this point. When I run the car on the standard ign map, the idle hunts around very impolitely. Any reason I shouldn't stick with the delta ign idle? Most guys with this engine idle around 9 - 12 degrees of advance.

[gti]

Sorry, what do you mean by there is no 3 wire.
You are using SM4.

[Ian]

There is no 3-wire. You run 2 wire and configure two outputs for the IAC out, with one inverted which balances the signal. Will try the ignition advance though.


You have it correctly configured as an output but you shouldn't select Bosch 2 wire type as that relates to the Bosch 516 idle valve which has a special default position and electrical characteristic. Linear would be a better choice but I have found that the 3 wire valves tend to have a more exponential characteristic towards either end of their travel. What it really needs is the User Defined characteristic but that takes quite some effort.

[turboe36]

Thank you for the tip Ian. I will try linear and see if that helps my issue.

[Chris]

It is running delta idle ign at this point. When I run the car on the standard ign map, the idle hunts around very impolitely. Any reason I shouldn't stick with the delta ign idle? Most guys with this engine idle around 9 - 12 degrees of advance.


You should stay with delta idle ign. The only time I dont use delta is if the installation does not have an idle valve or when I integrate with a factory ecu and the sm4 does not drive the idle valve.

Chris

[turboe36]

I changed over to linear valve type and added some timing at a 400rpm drop. It may be a little better, but hard to say. It still died on me once coming to a stop. I also tried dashpot settings, but they didn't seem to do anything at all.

Ideally I'd really like the idle to catch 1000rpm on the decel and then settle it to 800rpm like the factory management does. I'm going to mess with the stall saver stuff as well. Wish me luck!

[MRMRacing]

Do you have speed I/P connected?
Use Follower gain to 150, RPM atack to 2550, Stopped RPM limit 200, Stopped rpm decay start with 40 and try more/less until it drops slowly. There are more settings if you could post your latest cal file.

[turboe36]

Do you have speed I/P connected?
Use Follower gain to 150, RPM atack to 2550, Stopped RPM limit 200, Stopped rpm decay start with 40 and try more/less until it drops slowly. There are more settings if you could post your latest cal file.

Ahhh very good advice! I have the speed input hooked up but not calibrated. The speed reading is way off. I will try this. Thank you :)

Tonight I set stall saver to 25% at 950rpm :eek: and added some fuel on IAC movement. This helps VERY much. No more stalling when coming to a stop, and it only dips low when rev'ing at a standstill and abruptly closing the throttle plate. It is worse when I have fuel decel cut enabled. I made fuel come back on at 1600rpm and it seems to be happy. No stalling since. Will play with the follower settings. Thank you once again.

[turboe36]

Here it is. Thank you Chris!

http://www.smeraglinolo.com/private/NEW01.CAL

I updated this. It is now my current cal file.

[MRMRacing]

You have minimum IAC position to 45 at warm engine, you can adjust your throttle so it use less pwm at idle.

I have updated your cal file with the TPS follower, even thus you do not have the speed input connected you still can use this. Now when you rev engine it will settle 200 rpm above idle and drop with 40 rpm/sec to idle. If you have speed input connected it will idle 500 rpm higher as long as speed is above 15 km/h. It will also help rpm not dropping so fast so when you "hit" next gear it will just be right rpm. adjust Moving RPM decay for correct rpm.

If you change the throttle so IAC pwm at idle will be around 20 % you have to:

Set IAC min position to zero all temperatures
Change IAC Proportion Range to suit your IAC, test as help describes.
Adjust IAC closed rpm value from cold to warm while watching IAC adaption, adjust closed value until adaption is close to zero * (See below)
Monitor during warm up the IAC position and set IAC min position to 5-10 % lower values.Note that the IAC closed rpm and adaption works together on startup. If your car idles and stops at zero adaption the adaption will be stored in memory until next start, so if you have to high values at colder temperatures it will start and run to low until it adapts rpm. So I prefers to have little less IAC closed RPM values at all temperatures except operating temperature. Subs tract 200-400 from your table at all cells without operating temperature when finished monitoring adaption in step 3 above.

This makes colder starts smother since engine idles up and slowly adapts down to idle instead of starting and idle to low before adaption is made.

Adaption can be a problem if you use Automatic tranny since adaption is different if you stop engine just when you have put neutral in or wait in neutral until adaption is made. This is more noticeable on old automatic trannys.

[turboe36]

Wow! Thank you VERY much Robban. I appreciate you taking the time to help! :)

I will try what you suggested either today or this weekend, and report back.

Thanks again and have a nice day!

[Wroom]

...It is worse when I have fuel decel cut enabled. I made fuel come back on at 1600rpm and it seems to be happy. No stalling since...
One should set decel fuel cut recovery high enough in rpm so that engine is at normal combustion a while before it comes close to idle rpm's. Otherwise one will have to much "wrong data" in the IAC adaption. This time varies between engine models, and some engines can have fuel cut rec at 1400 rpm and other engines need this to be as high as 2400 rpm. The fuel cut commence should also be some 600 rpm, or more, higher than fuel cut rec for best performance.

[-Totenkopf-]

Is the bosch 3 wire valve a standalone unit or dose it have to be attached to a throttlebody (or have a couple of custom pieces fabbed up). I'm using the bosch 2 wire valve, however, have heard that the 3 wire valve can produce a better idle. The 2 wire valve just has 2 5/8" barbs on it. Is the size approximately the same as well? Mounting space is at a premium. If someone can get me a picture of the 3 wire valve I'd be most appreciative.

Cheers,

James.

[-Totenkopf-]

Another quick question on the ford 2 wire valve, does it matter which way this is connected, ie, which wire you hook up power and which wire you hook up the PWM output from the Autronic?

[Chris]

Some of the later valves have diodes in them

Chris

[MRMRacing]

Some of the later valves have diodes in them

Chris

Check with a multimeter - diod test for directtion if there is a diod.
The Bosch three wire is very like the two wire verison.

[-Totenkopf-]

Ah yes, I saw the motec drawing with the diode in it. The valve is still brand new, but a bloke had it for a while before me. I think it'd be relatively new. I do diode test and see what I come up with.

Thanks alot fellows. I'll probably have many a stupid question over the next couple of weeks.