Elevated (high) idle speed

[|sAs|]

Sounds very reasonable.. That would mean the ECU increases voltage to close the valve..?
question remains.. any chance of testing it out of the car? Should I do anything to it whilst it's out? (cleaning etc?)

 

[danb]

ah just realised you have stepper type, never seen one myself can only assume they work in the same way as the other type.

Dave is lurking to correct me no doubt.

 

[|sAs|]

More research have been done. This is as previously stated the stepper type IACV. It works by a spring-loaded rod valve in the housing with a membrane to control airflow. The motor is another spring-loaded rod that has some kind of electrically controlled spring rate.

My conclusion is that in "off" position it should be closed all the way with none or minimal air passing through, then as the ECU wants to open the valve it applies current to the motor which in turn makes the spring rate of the motor incrementally greater than that of the housing rod.

The problem for me is that when I put the motor and housing back together the membrane opens and lets air through causing the high idle. It seems as though the spring for the rod in the housing has become weaker than it should be, or something does not sit right in it. Unfortunately the housing seems to be a sealed unit and can't be investigated further without destroying it.
I'll try to soak everything in WD40 and leave for a few hours, then see if it is possible to put it back together as it should be.

I hope my poor English didn't make it impossible to understand

 

[DaveL485]

So the ECU is opening it too much?

There's a fault there somewhere then. The ECU should close the valve down if it idles too high, and open it up if it idles too low. It doesnt have a preset like 50%open=idle. It should adjust the valve to obtain the right idle.

I'd probably set up a variable resistor and a seperate control wire to test the IACV myself now, see if it's that or the ECU at fault.

 

[|sAs|]

The problem is that I can't get it to close at all. When the rod and the motor have contact theres another 3-4mm left before I can put in the screws. So when assembled it is open, which it shouldn't be according to my tests.

 

[danb]

source a replacement to test it?

 

[DaveL485]

Is it not adjustable on a thread?

 

[|sAs|]

Not what I've seen. Do you mean motor or rod?

 

[|sAs|]

I've replaced the IACV with a used one from Ollie, big thanks to him.

It lowered the idle speed from 1700 to 1400rpm, my next test will be lambda-sensor I think. What results should I look for?
Is the sensor bad if there is no change in idle speed?

 

[DaveL485]

Lambda won't affect idle speed. I ran without one for ages.....

 

[|sAs|]

Lambda won't affect idle speed. I ran without one for ages.....

Hi again. Thanks for all your tips and hints! I thought to let you know that it is now fixed, and I actually have a little bit too low idle this time, around 850rpm's but that will be easy enough to fix..
The problem was a crack in the exhaust system, just over where the lambda sensor sits. It was also the cause of a 1.06 lambda reading which caused MOT-failure. A couple of welds later and I have a reading of 1.00

I also got a XRD-display from the previous owner that helped me set the tps.. It showed that I had a tps-value of 50% with closed throttle.. That made it very difficult to drive with light throttle openings..

 

[DaveL485]

Cool! Nice one.