ICV, is this normal?

[flashBE]

Hi, my name is Ben and I'm from Belgium.

I'm having some problems with my M20B20 facelift model and I think it could have something to do with the ICV.

When idling, the engine is going up and down in its revs and it can only be neutralized for 90% by screwing the AFM screw completely down. No known air leaks.

I cleaned the ICV with carb cleaner and it didn't help. So today i took a better look at it. When turning on the ignition, the valve closes. It can be pushed open with a screwdriver, but it immediately closes again. (Not completely because I noticed carb cleaner leaks through.)

Also, it does make the buzzing noise, but i can't see anything spinning in there, even with the valve pushed open.

Is this the way it should be? Because I once left it unplugged and it didn't make any difference.

Thanks

[daimlerman]

Although you say you have no air leaks,this would be my first check.

Use an aerosol spray,WD40,carb cleaner,when the engine stabilises,that's your leak point.

The ICV is usually very reliable.

[sweep]

inlet manifold gasket?

[Grrrmachine]

By playing with the AFM screw, you have introduced a new problem to the car. You will need to take it to a mechanic with an exhaust gas analyser to reset.

Your ICV sounds fine. You really need to look for air leaks:

http://www.e30zone.net/e30zonewiki/inde ... #Air_Leaks

[flashBE]

The oil cap, crankcase ventilation hose, the rubber boot between the AFM and throttle body, the rubber plug under the TB, the hose between the inlet manifold and pressure regulator and the inlet manifold gaskets (new) are all fine...

[Grrrmachine]

If you're absolutely certain, then the next thing is the Throttle Position Switch which may get filled with oil. Then it won't send its Idle signal to the ECU, leading to the "hunting" you describe.

http://www.e30zone.net/e30zonewiki/inde ... ake#Idling

[flashBE]

By playing with the AFM screw, you have introduced a new problem to the car. You will need to take it to a mechanic with an exhaust gas analyser to reset.

Your ICV sounds fine. You really need to look for air leaks:

http://www.e30zone.net/e30zonewiki/inde ... #Air_Leaks

Really? I did notice it's runs quite rich when releasing the AFM screw again and the stalling idle gets worse. Fuel consumption now is ok though, 10.1l with a lot of highway roads.

The power also seems to be fine. But 1 other problem I have is that the engine shakes, stutters a few times when releasing or pressing the gas pedal when the engine has to deliver a lot of power, eg when shifting up to second gear.
I thought that could have something to do with the TPS. It's apparently mounted crooked and it doesn't read wide open.

[Grrrmachine]

The AFM screw is set at the BMW factory when the engine is first installed and running, then it's covered with a plug and never touched again. NEVER. By adjusting it, you're just covering up another problem by confusing the ECU.

It does seem like your TPS is either badly set up or not working.

[flashBE]

If you're absolutely certain, then the next thing is the Throttle Position Switch which may get filled with oil. Then it won't send its Idle signal to the ECU, leading to the "hunting" you describe.

http://www.e30zone.net/e30zonewiki/inde ... ake#Idling

I hope that's the problem. I do wonder why it's mounted crooked right now, the left side sits further to the inlet manifold than the right side.

[flashBE]

Could it be that the wiki is wrong about the TPS testing?

In the wiki it says that pin 1 and 3 should go short circuit when the TB is almost completely open, but here it says that pin 2 and 3 should go short circuit

And here it says that there should be continuity between the inner and the other of the outer pins, which is the same as in the Pelican article I guess. (Confusing sentence when English isn't your native language )

EDIT: Found it in the Haynes manual. The pin lay-out is 2-18-3.
There should be continuity between 2 and 18 when the valve is 0.2 to 0.6mm from the stop. There should also be continuity between 18 and 3 when the switch reaches 8 to 12 degrees before WOT. You should hear a click each time.
So I think the wiki is wrong.

[flashBE]

Soooo... I ran some electrical tests.

Turns out the TPS is just fine.

The resistance between the terminals of the ICV is also fine, 40 and 20 ohms. But when i pull of the plug with the engine running, nothing changes, idle remains at about 700 RPM.
So than I tested the voltage arriving at the ICV. The middle terminal to ground is battery voltage, and the voltage between the middle one and 1 of the outer ones is 10V, so that fine, but the voltage between the middle one and the other outer one is only 4.3V instead of 10V, so that's not OK.

I also checked the AFM using an ohmmeter on the ECU connector. While moving the flap, I get readings between 560 and 1040 ohms, but the resistance only starts changing when the flap is already moved quite a bit. Also not OK.

Failing AFM combined with faulty ECU or faulty wiring to the ICV? Or could it be that the 4.3V at the ICV has to do with a failing AFM or the other way around?

Normal:


Resistance starts going up from this point:


On a sidenote: My idle is actually quite allright. When releasing the AFM screw, you can hear the engine go "up and down" and smell that it throws a lot of unburnt gas out of the backbox, but no rev climbs and drops noticable on the meter.

[Manni198]

If it ant air leaks its the ecu I spent weeks fault finding it was fun believe me I learnt alot about my car witj that single problem. When I turn on my ignotion the icv wad being sognalled to fully open the cause was the ecu in the end their is some checks that can be done to tps and icv also air mass sensor. The last thing inwanted to do was replace ecu so triedy hardest to make sure it wssnt tje ecu. In the end it was. Luckily infound a friend with another one he sold me for 20 quid

[Brianmoooore]

You cannot reliably check an AFM with an ohmmeter. You need to connect a six or nine volt battery across the ends of the pot., and monitor the voltage on the wiper as you slowly push the flap open.
It is normal that the idle speed doesn't change when you disconnect a M20 ICV. If you increase the load on the engine, by turning all the lights on, you will see that the revs do drop, since the ICV can no longer compensate.
What engine ECU do you have? There's one that has a known issue with idle control.
Does your car have a cat. and lambda sensor?
It's not clear from your fault description whether this is likely to be an idle control problem or hunting caused by a weak mixture. Don't forget that it's easy to confuse a weak mixture for a rich one, as mixture that is too weak to ignite will appear in the exhaust as unburnt fuel.

[flashBE]

You cannot reliably check an AFM with an ohmmeter. You need to connect a six or nine volt battery across the ends of the pot., and monitor the voltage on the wiper as you slowly push the flap open.
It is normal that the idle speed doesn't change when you disconnect a M20 ICV.

Well, two things the Haynes manuel is wrong about then.

Can you explain the first sentence a bit more please? At which terminals do I connect the battery and at which the voltage meter?

Currently the 172 ECU is used with a Speedtouch chip. I still have a 163 lying around also.
No kat, no lambda.

I personally think it's a mixture problem, because the revs dont climb or drop as you see with an idle problem. The engine does make that typical sound though.

Thanks

[Brianmoooore]

Battery negative and black meter lead to pin 4, battery positive to pin 3, and meter red to pin 2.
172 ECU isn't the one with the problem.

[flashBE]

Someone offered me another one for free, so tried that one today.
What a difference! The hunting is gone, no more smell of unburnt gas, definitely more power and a better engine sound.
I think it all had to do with the adjustment screw. Thanks for making me aware of that.

Although, the few stutters(?) when quikcly pressing the gas pedal (+- 4 stutters) AND quickly releasing it (+- 2) are still there. If it only occurs when pressing it, it could have something to do with the fuel pump of filter, but what on earth can make my engine stutter when releasing the pedal??

[Brianmoooore]

Ensure that the throttle position switch switches as soon as the throttle butterfly moves off of its stop, consistent with switching back again reliably when the throttle is released.

[flashBE]

Ensure that the throttle position switch switches as soon as the throttle butterfly moves off of its stop, consistent with switching back again reliably when the throttle is released.

It does, i can hear the click and also tested it with an ohmmeter.
At which pins from the ECU connector can I test the wiring?

[Grrrmachine]

At which pins from the ECU connector can I test the wiring?

http://www.e30zone.net/e30zonewiki/inde ... CU_Pinouts