What does my ECU know?

[TheDutch]

I am trying to resolve this annoying idle problem I have on my iS, my latest suspect is the AFM. I have just got a replacement AFM off of smithy318i (good job that man) and want to switch them over for comparison.

NOW! I have two queries:

FIRST! Does the ECU 'learn' parameters from the AFM as it does for say, the throttle position (I think it does this in mine, at least), or are they preset values to which the AFM must comply?

SECOND! I wish to get the CO adjusted correctly for both AFMs for a fair comparison, can I just get them both done one after the other to achieve this?

LASTLY!

THANKS!

Neil

[Dan318-is]

fella im having an annoying idle problem also

does yours hunt between 500-11-- rpm and sometimes stall??

iv cleaned my idle control valve, secured and replaced all vacuum hoses, replaced inlet manifold and throttle body gaskets and it still idleing silly

have you tried the DME relay or Temperature sender iv heard that these are also suspects?

[TheDutch]

Well the idle is not as bad as that, and the car has only stalled twice in two years (when steering was on full lock at idle), so it doesn't sound as severe as yours. I've done:

ICV checked, cleaned + exchanged

Blue temp sensor checked

AFM checked

Hoses accessible without inlet manifold removed checked; main bellows to throttle body replaced

I built a diagnostics interface and checked error codes - none present (amazingly!)

Throttle Position Switch checked (318iS has more modern potentiometer type)


I don't think the symptoms are likely to be DME relay-associated. If it's not the AFM my next target is to dismantle the intake manifold and check hoses + injector o-rings as it tastes like an intake leak to me. Was it difficult to take all that apart?

Apart from this the engine runs ok, good performance and economy so it is nothing major, but a niggle I've been trying to fix since I got the car!

Have you heard your ICV buzzing, or you can look at the valve operating by starting the car with the pipes disconnected; mine turned slowly and smoothly as it tried to modulate the airflow.

Let me know if you want to check temp sensor or TPS, I have some correct values.

Neil

[Dan318-is]

mine is soo annoying at the mo

the inlet manifold throttle body is just unbolting but some bolts are fiddly and well easy to drop

you need a new inlet manifold gasket (5.50)

and two throttle body gaskets (about 1.80)

i replaced these

as for DME relay and temp sensor, they are my next targets.

my IVC, iv tapped it when running like i was told to and it still doesnt change it. what happens if u run the engine with the IVC disconnected at hoses?

[TheDutch]

Running engine with the ICV hoses detached made mine splutter and cough ten times more. Only did it for a few seconds though.

Here is some temp-sensor stuff I think I got off here previously :

Blue Temp Sensor
It's located just below inlet ports 2 and 3. i.e. 1/2 way back the left side of the engine under the inlet manifold and is not the easiest place to get.
To test it you measure the resistance between it's two terminals.
These figures are actually measured off a good sensor:
Cold water : 3400 ohms
Hot water (from tap) : 980 ohms
Very hot water :306 ohms

If your sensor is faulty, you will get higher readings than these.
In the example I mentioned in my previous post,(also an M40), the readings were about double.

Hope that's of some use... good luck

Neil

[Brianmoooore]

If you look at one of my posts from about six weeks ago, you will see that I had a duel fuel 325 M20 which missfired on idle on petrol (no lambda control), and missfired and hunted badly on LPG (under lambda control).
It took me ages to find the problem, ( 1/2 the inlet manifold gasket missing on No 1 cylinder), because the leak was absolutely silent. So silent, that even when I knew where it was I wasn't convinced, even with a length of hose near the join and the other end in my ear.
Final proof was obtained by taking a gas blowlamp (type with seperate torch and gas bottle), removing the shroud and gas jet, and pushing the end under the manifold with the gas turned partly on. As soon as gas got near the leak, the engines response was obvious.
Similar things can be done with carb cleaner aerosol.

[TheDutch]

OK so changing the AFM didn't really help matters so I'll replace the intake gaskets.

318-is - Did you replace both the intake manifold gaskets? There is one to the head, and one joining the two halves of the manifold.

I have ordered both either way, and a load of rip-off o-rings for the injectors (Ԛ£14ish!)

La-da-dee... lets hope it all helps eh? More news soon.

Neil

[Dan318-is]

no i only did the green one mate

[jaistanley]

Dan (318is)...

Are you still having problems with idle? My 'is' had a nightmare idle and would often stall. Fixed by cleaning the crank position sensor and re-setting the cam timing (mine was WAY out). Now it's rock steady all the time.

Jai

[tomstickland]

It's worth checking the idle control valve pipes for air leaks too. Mine didn't idle so well after I replaced the timing chain - turned out that one of the idle control valve pipes had torn slightly and there was a small air leak.