Clean your ISV!!!!
11-23-2008, 07:15 PM
#1
Race Director
Thread Starter
Clean your ISV!!!!
During last weeks flappy replacement Bill and I also replaced my ISV with a new one ($295 ouch).....sharky had a low odd idle for a while....that a bit of WD40 down the vac line to the ISV would fix for a while.....
So after I put the new ISV in, things are much better...far more stable idle...no more low 450rpm almost gonna stall when cold idle...
My old ISV was caked with lots of sticky black grease-dirt....so when I tested it with a 12V power supply I could feel the ISV motor engage, but the valve would not open!!! I'm guessing once the engine warmed up it would free itself and work properly....
So I cleaned my old ISV today and tested it again.....when dirty it wouldn't open...and when I opened it with a screwdriver it stayed open against the spring force....after cleaning it it opened and closed as it should and would not stay stuck open when opened manually.......
So the moral of the story is you may not need a new ISV....a good cleaning of your existing ISV may be enough?
So after I put the new ISV in, things are much better...far more stable idle...no more low 450rpm almost gonna stall when cold idle...
My old ISV was caked with lots of sticky black grease-dirt....so when I tested it with a 12V power supply I could feel the ISV motor engage, but the valve would not open!!! I'm guessing once the engine warmed up it would free itself and work properly....
So I cleaned my old ISV today and tested it again.....when dirty it wouldn't open...and when I opened it with a screwdriver it stayed open against the spring force....after cleaning it it opened and closed as it should and would not stay stuck open when opened manually.......
So the moral of the story is you may not need a new ISV....a good cleaning of your existing ISV may be enough?
11-23-2008, 08:49 PM
#3
Race Director
Thread Starter
11-23-2008, 11:13 PM
#5
Rennlist Member
I cleaned mine with varsol/paint thinner, then degreased it with brake cleaner then a slight lube with WD40.
Did the same tests as Brian worked perfect.
Did the same tests as Brian worked perfect.
11-23-2008, 11:29 PM
#6
Burning Brakes
Brian
Nice R/R of the old ISV. To help you feel a little better about spending $295.00 I replaced my ISV a few years ago and got a better idle as this seemed to be the problem. After my recent engine pull I noticed the idle would surge a bit when I would blip the throttle.
I cleaned my old ISV ( this is why I keep my old parts) the same as you did and tested. It seemed good so I took out the "new" ISV and replaced W/ old/cleaned ISV and had the same "old" problems I had a few years back W/ unstable idle. Put "new" ISV back in and had good steady idle. (still have to figure out the blip/surge thing)
So even tho the ISV cleaned/tested may seem ok it still could be a problem.
However to save money it would be a good way to see if this would fix a "sticky" ISV. I forget on the S4's how easy/difficult it is to get to but on the 85/86 it is not that bad.
Nice R/R of the old ISV. To help you feel a little better about spending $295.00 I replaced my ISV a few years ago and got a better idle as this seemed to be the problem. After my recent engine pull I noticed the idle would surge a bit when I would blip the throttle.
I cleaned my old ISV ( this is why I keep my old parts) the same as you did and tested. It seemed good so I took out the "new" ISV and replaced W/ old/cleaned ISV and had the same "old" problems I had a few years back W/ unstable idle. Put "new" ISV back in and had good steady idle. (still have to figure out the blip/surge thing)
So even tho the ISV cleaned/tested may seem ok it still could be a problem.
However to save money it would be a good way to see if this would fix a "sticky" ISV. I forget on the S4's how easy/difficult it is to get to but on the 85/86 it is not that bad.
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11-23-2008, 11:45 PM
#9
It is an electric motor with brushes and coil windings and just like all the other electric motors in a 928 they wear out . A weak motor might get stuck easier than a new one. If the part was only $50 few would think twice about changing it. The S-4 it takes several hours to take off the intake and swap it out. Should the cleaned out idle stabilizer not work it is not a very good hourly wage doing the job a second time and not all that much fun.
11-23-2008, 11:59 PM
#10
Rennlist Member
Such a common failure might be a candidate for underhood relocation. Just rubber hoses of a different length, plus slightly longer electrical control wires, right?!
11-24-2008, 12:05 AM
#11
As I recall, on DR's supercharged engines the ISV is indeed relocated to a much more accessible (sensible) location. I'm also advised that it is not impossible - though difficult- to remove the ISV and relocate on an S4 without removing the inlet manifold. Confirmation on either of these impressions would be welcome.
11-24-2008, 12:09 AM
#12
If you used longer hoses it might change the response time. It cycles multiple time per second to constantly hold the correct idle speed. It does not open part way as bleeder , does not get a variable current but it is either open or closed. Darn things just do not last. Every 10-15 years you might need one.
11-24-2008, 12:46 AM
#13
Nordschleife Master
guys the factory location for the ISV is perfect, its out of sight and does its job well when its working correctly.
The fact that you would bother to relocate it seems silly. It needs to be replaced once every 20 years. This is not a common failure here.
I replaced the ISV on my old GT and would reccomend the same to anyone while they are in there. It does improve idle quality and while your at it replace the crank position sensor too.
The fact that you would bother to relocate it seems silly. It needs to be replaced once every 20 years. This is not a common failure here.
I replaced the ISV on my old GT and would reccomend the same to anyone while they are in there. It does improve idle quality and while your at it replace the crank position sensor too.
11-24-2008, 12:15 PM
#14
Race Car
You do not need to remove the intake to replace the ISV on any '85+ 928. You just need small hands and be able to lie down on the top of the engine. Working with things by feel also helps, but it is definitely possible.
Dan
'91 928GT S/C
475hp/460lb.ft
Dan
'91 928GT S/C
475hp/460lb.ft
11-24-2008, 12:28 PM
#15
Three Wheelin'
Join Date: Sep 2007
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Hello Brian,
Great post. I've got mine out now (as well as most of the engine disassembled) and like you, I bought a new ISV as part of Virginia's engine refresh. I was wondering how to clean and test the old one just for curiosity and your post hit the mark. I'll play around with it after I get things put back together and running. BTW, what kind of 12V source did you use (car battery, AC/DC converter....??)? THANKS!
Great post. I've got mine out now (as well as most of the engine disassembled) and like you, I bought a new ISV as part of Virginia's engine refresh. I was wondering how to clean and test the old one just for curiosity and your post hit the mark. I'll play around with it after I get things put back together and running. BTW, what kind of 12V source did you use (car battery, AC/DC converter....??)? THANKS!