E30 Zone

I'm trying to sort out my high idle and, what smells like, rich running. The idle sits consistently at around 1100rpm, with no hunting. What are the usual culprits of a high but consistent idle?
I was going to check the ICV is working correctly. It's just a solenoid that is opened and closed by the ECU to achieve an rpm in a certain range (~700rpm?), right? Does anyone know what signal it should get from the ECU? I was going to measure the signal at the connector. Also, what should happen if the connector is disconnected? I tried last night and it didn't change anything
In terms of the rich running, I guess the most likely culprit is the blue temp sender. I've checked this before on the sensor, but would like to make sure the signal is making it to the ECU. Mine's a '87 325i with an 0 261 200 073 ECU. Can anyone tell me which pins I check on the ECU for this?
Aside from that would adjustment to the AFM bypass screw lean the mixture? What CO value am I looking for when adjusting this?

If you can answer one or all of these questions that'd be really helpful.
Cheers,
Finn

Today I tried to diagnose my idle problem. I removed the ICV and disconnected the cable. Then I started the car with the two holes blocked off to represent a completely sealed ICV. Idle was ~700rpm like this. From what I've read elsewhere I think this is too high for this condition.
I adjusted the throttle stop to get this down to the limit of stalling (approx 500rpm) with the holes blocked off. I then put the ICV back on the car and the idle was back to ~1100rpm. I guess this means the ICV is not shutting properly.
Should it be able to provide a complete seal so there is no air bypassing the throttle? Will it definitely be the ICV itself that's the problem? Is there any way of checking it's getting the correct signal?

If anyone can help that'd be great...

Finn

I think the way it works is the throttle position switch detects when the throttle is shut and opens the ICV to allow enough air in to run the engine at idle with the idle speed and fuel delivery managed by the ECU.

The throttle stop screw will only control the idle speed by overriding the ECU.

DHFiS wrote:I think the way it works is the throttle position switch detects when the throttle is shut and opens the ICV to allow enough air in to run the engine at idle with the idle speed and fuel delivery managed by the ECU.

I think you're right on that. That's how I understand it.

DHFiS wrote:The throttle stop screw will only control the idle speed by overriding the ECU.

I'm not sure what you mean here. My understanding is by adjusting the throttle stop (which you shouldn't do normally, my mistake!) you vary the proportion of air through the throttle and through the ICV. If you set the throttle completely closed at idle, then the ICV should be more open. If the throttle's set a bit too open at idle then the ICV will be more closed. The ECU should balance the 2 by varying the ICV opening. Is this not right?

Also, I forgot to say before, my ICV (L-shaped) is push fit to the 2 rubber hoses with no jubilee clips and the metal piece that comes off the ICV and fits in the engine-side of the throttle doesn't have any rubber seal. Is this right? Seems odd not to have a better seal on the intake system...

AFAIK The ECU is programmed to idle the engine at the rpm given in the handbook, once its over that figure either there is a fault with the ECU or the throttle is open and the ECU is not controlling the idle speed. Brianmooore will know better than me though

Brianmooooore! Are you out there?

Bump for Brianmooore...

To summarise: my car idles at a very consistent ~1000rpm. There's no hunting, and it's consistent hot or cold. If the ICV is removed and the holes blocked, the idle comes down to ~500rpm (just on the limit of stalling). The ICV is clearly allowing too much air to pass the throttle to achieve the ~650rpm idle. Is this likely to be an ICV problem (it's been given a good clean) or an incorrect signal from the ECU? Is there any way of testing the ECU signal to check?

Cheers

Freynolds,

You need to get an answer off a Brianmooore-type knowledge-brain as to whether your car should idle at 500rpm with the ICV tube blocked off. ANYONE????

Remember I said (on another idle post) I thought that the car should stall, and that at somepoint the throttle stop had been adjusted? Did you try closing the throttle stop back up so the car stalls without the ICV?

jslot wrote:Freynolds,

You need to get an answer off a Brianmooore-type knowledge-brain as to whether your car should idle at 500rpm with the ICV tube blocked off. ANYONE????

Remember I said (on another idle post) I thought that the car should stall, and that at somepoint the throttle stop had been adjusted? Did you try closing the throttle stop back up so the car stalls without the ICV?

I'm sure I've seen Brian mention that the idle should be ~500rpm with the ICV blocked off. I'm trying to attract his attention to this thread...

I'm not keen to close the throttle up any further as it seems to make no difference to the idle speed, and I believe they're not meant to be fully shut (doesn't it risk sticking???). To my inexperienced brain, it appears the ECU is just targeting an incorrect idle speed, either through the wrong signal or reading the wrong engine speed. Or the ICV is interpreting the signal wrong.
I'm keen not to waste any of my hard-earned, so want to know if there's anything I can check to prove it's the ICV or ECU before I buy a replacement.

Cheers for your help

I'm no Brianmoore but....

When someone recently opened up my throttle stop (they were supposed to be looking after the car) the engine revved at about 450-500 and stalled occasionally. I fixed it by screwing the throttle idle back until the TPS closed, idle returned to 700.

As far as I know, when the TPS is opened by fiddling with the throttle stop the ECU will close the ICV completely.
I've no idea what the ECU does if the throttle is open and the TPS says it's closed as this should not happen.
If the TPS is closed the throttle should be completely closed, and so the ECU will open the ICV until ~700RPM is reached.

It's possible that either your ICV or TPS is faulty, but you still shouldn't need to mess with the throttle stop.

Throttle stop and bypass on the AFM should never need adjusting. If adjusting them improves matters then you are just masking another fault, and making diagnosis even more difficult.
The throttle stop is set up by replacing the ICV with a special fixed air bleed valve, then setting the idle revs with the throttle stop to a certain value.
When I've run an engine with the ICV blanked off, they generally run very lumpy and on the point of stalling, so somewhere around 450 RPM I would guess.
Set the stop back like this, and check (electrically) that the TPS operates when the throttle moves just off of the stop.
ICV is a rotary solenoid, balanced between two opposing coils, and should just stay put when the plug is removed.
Your OP mentions rich running, which suggests that the ECU may think the engine is cold, and increasing the idle speed to suit.
You mention checking the blue temp sensor signal at the ECU plug, which is indeed what you should be doing.
If your ECU has a 55 pin connector, then the coolant temp sensor signal is a brown/red wire on pin 45.
Measure the resistance between this pin and earth with the engine cold, then reconnect it and run the engine up to full temp, then unplug it and measure again.

Thanks Brian.
The rich running is now sorted. I think someone before me had tampered with the AFM screw. I had it in the garage on Saturday and set the lambda to 1.00.
I've got the blanked-off idle speed set to around the stalling level already, but will need to adjust the TPS position (at the moment it needs a bit too much movement off the stop to click). The TPS has been checked electrically recently and was fine - will double check though.

I will look into the whether the ECU is getting the right temperature signal too. Is this just a case of pulling the large connector from the ECU housing and getting a multimeter on the pins in the connector?

Brianmoooore wrote:When I've run an engine with the ICV blanked off, they generally run very lumpy and on the point of stalling, so somewhere around 450 RPM I would guess.

This is set to just above stalling now.

Brianmoooore wrote:Set the stop back like this, and check (electrically) that the TPS operates when the throttle moves just off of the stop.

The TPS works fine from closed, through click to WOT, and is set to match the throttle stop now.

Brianmoooore wrote:If your ECU has a 55 pin connector, then the coolant temp sensor signal is a brown/red wire on pin 45.
Measure the resistance between this pin and earth with the engine cold, then reconnect it and run the engine up to full temp, then unplug it and measure again.

Mine's the smaller 35pin connector (pin 13 for coolant temp I believe). At cold today it was 3100ohms, and after a little warm up drive it was 285ohms. I think these are about right. With this checked, I'm happy the rich running is fully sorted. It's just the idle now.

Is there anything else I can check to prove it's the ICV? Input signal etc? Would the ICV fail in such a stable manner? Should I just buy/borrow a replacement and try that?

Cheers,
Finn