ICV surging mystery solved...?

[Lammers]

Nobody seems to realize that the ICV works on 9v not 12v, The ECU sends 9v signals. I got a new aftermarket icv and it gave me all the usual symptoms (basically the new unit has too much resistance and 9v will not close it),it would get the signal to open at start but would not close properly later since the icv has no default location. I found an original one, refurbished it and now my car works perfectly. A 12v test will tell you nothing, I saw a guy who recommends 6v, I did measure the voltage going to the ICV and it is 9v. This voltage discrepancy is what is driving everybody nuts, it is not closing properly, sometimes it end up in the right position thats why once in a while the revs look ok or your revs are fluctuating without logic.

[mysocal911]

Originally Posted by Lammers

Nobody seems to realize that the ICV works on 9v not 12v, The ECU sends 9v signals. I got a new aftermarket icv and it gave me all the usual symptoms (basically the new unit has too much resistance and 9v will not close it),it would get the signal to open at start but would not close properly later since the icv has no default location. I found an original one, refurbished it and now my car works perfectly. A 12v test will tell you nothing, I saw a guy who recommends 6v, I did measure the voltage going to the ICV and it is 9v. This voltage discrepancy is what is driving everybody nuts, it is not closing properly, sometimes it end up in the right position thats why once in a while the revs look ok or your revs are fluctuating without logic.

That's not correct! First, the center pin on the ICV is 12V from the same source as the DME ECM. Next, the DME ECM doesn't "send 9V signals" to the valve.
It pulses the two outer pins to ground, to vary the intake air that bypasses the throttle butterfly. It's that simple. When the windings become shorted,
the DME ECM idle output driver transistors typically fail, resulting in no idle control.

[Lammers]

I measured the center female to both outside grounds and both times it said 9v. I might describe the process wrongly, but I put a refurbished oem ICV into my car and the all my issues went away, I think that an aftermarket ICV will open correctly at startup but will not close correctly because the impulse or grounding or whatever is 9v and it needs 12v, an oem will close on 9v. it's the only conclusion I can make from what I measured and what the results are. The only thing I have done is replace my aftermarket ICV with a refurbished ICV, then I adjusted the idle valve and now it idles perfectly regardless of engine temp. BTW that bypass you have to do with the electric jumper on the drivers side of the engine bay, this works only when the engine is cold, correct?

[mysocal911]

Originally Posted by Lammers

I measured the center female to both outside grounds and both times it said 9v. I might describe the process wrongly, but I put a refurbished oem ICV into my car and the all my issues went away, I think that an aftermarket ICV will open correctly at startup but will not close correctly because the impulse or grounding or whatever is 9v and it needs 12v, an oem will close on 9v. it's the only conclusion I can make from what I measured and what the results are. The only thing I have done is replace my aftermarket ICV with a refurbished ICV, then I adjusted the idle valve and now it idles perfectly regardless of engine temp. BTW that bypass you have to do with the electric jumper on the drivers side of the engine bay, this works only when the engine is cold, correct?

A used one, right?

Use an oscilloscope and not a voltmeter to analyze what's occurring, for a better understanding of the problem.

[Lammers]

the problem went away with the used one, I will take a hard look at the aftermarket one I pulled out

[mysocal911]

All the original good one's, i.e. old new stock, are no longer available because over the years many mis-diagnosed idle problems as being the ICV.
The same happened with mis-diagnoded AFMs, i.e. no more old new stock.

[Lammers]

Originally Posted by mysocal911

All the original good one's, i.e. old new stock, are no longer available because over the years many mis-diagnosed idle problems as being the ICV.
The same happened with mis-diagnoded AFMs, i.e. no more old new stock.

It was incredibly easy to rebuild, hardest part is opening it up but it's a rather forgiving hunk of metal. Once open, there definitely was carbon build up and light rust in the motor area of the ICV from being 40 years old.

[76FJ55]

Actually if you look at the electrical diagram you can confirm that you should have 12V supply from the fuel pump fuse through the DME relay to that ICV. The power is not provided by the computer. the computer only controls the gerund path for the ICV. see image below of the wiring diagram tracing the ICV power.




as for the engine temp the engine should be fully up to operating temperature. the manual references 90C (194F) at the beginning of the idle adjustment procedure. you should adjust the mixture first before adjusting the idle speed, then reconfirm/adjust mixture accordingly. is may be an iterative process to get them both within spec depending on how far out the starting point is.