Unstable at idle speed

Here is what is happening to me. When you take off the rubber hose that conducts air from the throttle body speed is stable. By adding and releasing the gas pedal revs to stabilize in the second. When I return hose back, accelerator pedal and let the gas pedal speed has little variation. :nonod:
IACV new. When I close the tube with my finger, the motor is turned off.
I did a reset.
I believe the ECU-IACV are not communicating. My suspicion because when I separate the connector from IACV, no variation, tachometer needle is sharp as a sword.
Regards.

"M A D N E S S" - Crazy rover 25 (video) :sick:
It leads me to madness. This is a mystery that no one MG-Rover forum I found a solution to the problem. Who had a similar problem and how it is resolved?
I would ask all members who have any suggestion to remove this problem.
Thanks.

Vladimir,

that is the Iacv.
get the engine hot, then disconnect the electric plug on the IACV.
What is the idle speed?
Is it steady?

David Aiketgate wrote: Vladimir,

that is the Iacv.
get the engine hot, then disconnect the electric plug on the IACV.
What is the idle speed?
Is it steady?

David yes, when I turn off the cable from IACV in the old and the new IACV, speed is stable and the tachometer needle is sharp as a sword.

What reading is it at?. It should be 875rpm

If not adjust the set screw on the throttle body to give 875.
Refit the IACV plug.
Reset the Thottle position sensor.

David Aiketgate wrote: What reading is it at?. It should be 875rpm

If not adjust the set screw on the throttle body to give 875.
Refit the IACV plug.
Reset the Thottle position sensor.

my bue F had that done scew turned and re set the throttle position all ok for a couple of days then problem came back
as said it was an ecu fault in the end

ANGEL BOY on . org has the car now and BROON helped change the ecu so might be worht having a chat with them :broon:

Just looked at the video.

Could it be a purge system fault?

When the system purges the fuel fumes from the charcoal cannister back into the induction system it can make the revs rise for a short period, but the MEMs should compensate so you hardly notice.

There could be a problem with this system as it is purging too often.

CJJ I am not well understood. I ask that you please write a little more detail. Do you think that the evaporative Emission Cannister is defective, the valve on it, the ECU or something that I mentioned. I do not know the system very well. Really appreciate your help.
Regards.

The purge system shouldn't come into use unless above 1800 revs and temp sensor senses the engine is warm, but it is worth a try.

It could be many things to be honest.

What I would do is disconnect the purge system pipe from the induction system, also the brake vacuum pipe etc. and blank them at the inlet manifold so that no air can get in.

Try this for all the vacuum feeds and see if the idle stays constant.

Obviously don't drive the car like this as you will have no brakes.

I would also be tempted to unplug the IACV and see if it idles ok.

You may find that it doesn't idle at the correct rpm, but what I would be looking for is what is causing the sudden raise in rpm.

Something is injecting air into your inlet manifold. The way the video shows is too controlled for it to be a standard vacuum leak, so you are looking for a system that is injecting air at regular intervals.

CJJ I tried to turn off IACV cable. I wrote in earlier post.
Then everything is perfect. This led me to buy new IACV. But the problem is still there.

David Aiketgate wrote:
Vladimir,

that is the Iacv.
get the engine hot, then disconnect the electric plug on the IACV.
What is the idle speed?
Is it steady?

Vladimir
David yes, when I turn off the cable from IACV in the old and the new IACV, speed is stable and the tachometer needle is sharp as a sword.

That doesn't mean it is the IACV at fault though. It might be doing what the ECU tells it to do.

The ECU may be receiving a signal, or thinking it is receiving a signal from another system, so is opening the IACV to compensate.

I have U380 OBD 2 II EOBD Car Diagnose Tester Scanner, not report any error.
Would you be so kind to list the potential sources of possible causes. Which way to go in order to overcome this problem.
Thanks.