What tells how to run the ICV?

[b*saint]

What is the DME watching so it knows to activate the ICV? And what does the circuit look like on the ICV side? It doesn't run through any fuses or relays right?

[SpecM]

it looks at idle speed and water temp

[Need4Speed1299]

Throttle Position Sensor.

[b*saint]

So far we have the crank position sensor, dme temp sensor, and tps.

[jlevie]

Engine speed, engine temperature, and the A/C on signal are the dynamic inputs. Whether to use those inputs for control of the ICV is determined by the state of the idle switch in the TPS.

[b*saint]

So what is the camshaft position sensor used for??

[jlevie]

Oh this is a 318?

[b*saint]

yea its an m44. but I imagine Bosch didn't change what variables would command the icv from E30 days. Now Im looking at this from a plc idea. Input x y z means output a (icv) is this value via DME. Im pretty sure they aren't physically linked via mechanical relays.

[DJB]

The early Motronic system used a separate module to control the idle speed.

The later system ("i" engines) simplified this by putting idle control into the engine computer.

The ICV allows air to bypass the throttle plate. At idle, the throttle should be completely shut. The only air getting to the engine should be coming through the ICV.

The ICV is a spring-loaded flap that is opened by a solenoid. (Actually, I believe that it's normally open device, and that applying voltage causes it to shut, but that is just an implementation detail. It's easier to understand as opening.) A solenoid operates quickly, but it can really open or release the flap. So the computer controls it by sending a PWM "pulse width modulated" signal. The computer sends it pulse stream, making the pulses wider when it wants the ICV to open more. This is the buzz you feel when the ICV is operating.

The control for this is pretty simple. The computer knows that it should idle when it sees the throttle position switch in the closed position. It picks an idle speed based on conditions (e.g. warm coolant, A/C compressor on). If the engine drops below this speed, it increases the pulse width. If the goes above, it reduces the pulse width.

Note that this control system doesn't need to interact with the timing or the mixture. It's simply concerned with adjusting the pulse width, letting more or less air bypass the throttle plate. The rich/lean feedback loop from the oxygen sensor handles the injector pulse width. The ignition timing at idle is entirely from the RPM map.

[b*saint]

So I bet my crankshaft speed sensor is shit. I have a check engine light on but havent got it scanned. I dont know if it has anything to do with it because its had a rough idle since before the light. I also notice a lot of skipping. I figured it used a pwm to control it. I didnt think it was a pid, it looks too simple.

[nando]

So what is the camshaft position sensor used for??

sequential fuel and spark.

[nando]

So I bet my crankshaft speed sensor is shit. I have a check engine light on but havent got it scanned. I dont know if it has anything to do with it because its had a rough idle since before the light. I also notice a lot of skipping. I figured it used a pwm to control it. I didnt think it was a pid, it looks too simple.

if your crank sensor went bad, the engine shouldn't even run.

[b*saint]

Ok well I did a test. I set the idle return screw so it idled a little high. Then turned off the car. Restarted and the ECU readjusted for the throttle plate being a little open and it returned my idle to what its suppose to be. So I KNOW the icv and ecu is working. Now Im back to a really bad vacuum leak somewhere.