E30c M40 ICV test

[bad_robot]

The ICV for a 1990 E30c M40 engine is behind the engine at the top of the it. It has a Bosch electric connector with a short rubber tube inlet and its outlet is pushed into a rubber grommet into the top of the engine. A band holds it in place. I have disconnected it and cleaned it - shutter turns easily and springs back to its home location - clean inside.
I get poor idle particularly when the air con is turned on (revs increase which i know is normal but these revs are a bit too high). Tried to fix revs using the idle screw on the top of the engine but it does not hold the idle.
When car put into drive, revs drop and car tends to be too slow with a slight shudder at take off as revs too low. Increasing revs using the screw helps raise revs and remove hesitancy but then revs are too high when in neutral so probably using too much fuel.
Car goes ok when in drive. Only a problem when in neutral or air con turned on. When stopped in drive, revs ok but not perfect, but a bit high. Car starts ok. effect more noticeable when engine warmed to operating temperature. Engine temp is ok - fan ok, radiator is just 2 years old.

How do i test the icv?
is there another sensor that i may need to check?
Any thoughts about what else i can try?

O2 sensor changed about 2 years ago (9,000km) as well as leads, coil and distrib cap, plugs changed, petrol filter changed, air filter changed, Injectors replaced, too. But not in response to this idle problem which started just a month ago.

[ClassicSkril]

I had a similar issue and thought it was my ICV as well. However, it was my vacuum lines. After 190k my ICV was in need of a clean, and after several cleaning attempts it has been working fine. I would inspect your vacuum lines as they are cheaper to replace than an icv (if you do the mess under the intake mod)

[bad_robot]

Tks Classic

Sounds like a good place to start.


Any special location to look for the vacuum line?

Where or what is the mess under then intake mod?

[ClassicSkril]

Yea basically the hoses that connect to the ICV check for splits, both upper and lower were split on mine. Also there is a short little tube with green writing on it right below your throttle body. And the one at the front of the engine that connects to your valve cover. The rest of the lines can only be accessed through removing your intake manifold.

The mess under the intake mod is a process involving removing and replacing all your vacuum lines with generic vacuum lines from the auto parts store and the end result is an simple route for your lines, and also easy to access.

[bad_robot]

And dont forgat the gasket.
When replacing that, there will also need to be a need to change the water cooler tree.
To test for a leak, spray some carburettor cleaner at the gasket/seals and the engine revs will immediately increase proving a leak.