MainePorsche

Guys,

I have the ISV out. Doesn't look to soiled. Easily opens and closes when I put a 3 mm Allen shaft in the 'testing' hole.

I wanted to give a test to the valve function, so I used a 9 volt battery. I had the battery ground off for the intake removal. The valve only opened about 25 - 33 %.

My question is the following. Would having 12 volts to the valve give complete opening ? I assume yes in that there is not enough energy potential (with 9V) to the mechanical portion of the valve. I don't think it is just a matter of having some amperage to actuate the mechanics. I haven't applied 12 volts from my hot post for I am loathe do to so with the intake dissected.

Thanks in Advance.
Craig

WallyP

It should - I would just tap or momentarily touch the power connection (body grounded, of course) with a 12 vdc test lead, and would expect the valve to flick open, then close as soon as the power is removed. It is computer-controlled, and the computer quickly turns the power off and on - the duty cycle determines how open the valve is at any moment.

MainePorsche

Wally,
Thanks very much for that information.

StratfordShark

I've tested 2 (one old, one brand new) ISVs on bench when I did intake refresh.

Both opened 100% using power from fresh 9V PP3 type battery. They operated very snappily at that voltage.

What 9V source are you using?

MainePorsche

A simple 9V Duracell battery.

MainePorsche

Just a little update on my findings so far.
With 12 V the ISV opens briskly and completely. I guess the 9 V Duracell can't power it through.

davek9

I've used a 9v battery in the past in an 85/86 ISV, they are a different type, but it did open/ close.
Yours could be going bad if a higher voltage is required?

MainePorsche

This is precisely my concern.
I was just wondering if anyone out there had the same, or similar, testing results.
As it stands now, I don't feel I have compelling enough diagnostic evidence to change it out.
Note it was somewhat 'gunked up' prior to the 12 V testing. Was well cleaned prior to the 12 V trial.

MainePorsche

Also to note, the 9 V Duracell had 8.4 V.

davek9

The PIA is that on an S4 that ISV can't be removed w/o removing the intake, correct?
You may just want to replace it depending on mileage, also something to note, don't rule out the computer.
I swapped out two used ones only to find I had bad driver transistors on the board, my symptoms were it would work great when cold and hot, then out of nowhere she would go to 1500 idle. Would not return to normal operation until sitting over night.

Dave

MainePorsche

Dave,
Yes, I was considering that as well. I wanted to go step wise to diagnose matters. My MAF is clean and resistances check out according to John Speake's writing. It is very clean. My symptoms have progressed from only on cold starts to hot starts and while running. The idle surge up and down with the same frequency as the fuel pump sound. That is next to look at. Initially when only on cold starts it would surge up and down from 700 ish down to 300 and then stall. I would get it out of the driveway and drive it for two minutes and then it would stabilize and purr normally. Now it doesn't. My Temp II is resisting to spec.
I'll get it right.
Thanks,
Craig

ROG100

I have new ones for $140 8>)

MainePorsche

Thanks Rog,
I may be calling you for a fuel pump however.

the flyin' scotsman

Craig.......I have replaced 3 ISVs on various 928s primarily for 2 reasons; age and lack of accessibility. The intake R&R is not too bad if your familiar with the system and dont mind going back in if something else requires repair/replacement but for myself with such a short driving season and reasons stated I replace the valve for peace of mind.

I apply same 'logic' to all other components under the intake........YMMV

MainePorsche

Hey there Malcolm,
Been following your bearing issue. Glad you finally got it sorted.
ISV - I wanted to bench test it before changing it out. I'm not convinced it's the source of my idling issue. I'm going to work through a few other issues first. If it turns out I need to change the ISV I can have the manifold off in 1 hour solo or a half with my sous chef (my son).