I have found some good threads on the ISV but nothing that tells me how to test it. I did add 12v poss and neg to each end at it rotated. Reversed polarity and it switched back. I'm not sure what the center pin does. Is there a good test I can do to ensure it is working properly?

Thanks
Sean

 

I believe that's all you need to confirm on the ISV. MIne is an '89. I sprayed a bunch of Kroil (really good WD-40...) into it and cleared all of the carbon out of the unit. Works (and rotates) perfectly and the car maintains a nice steady idle.

 

How many miles on it? The S3 versions wear out, best to replace if original. (S4 type is a bit better design, AFAIK.)

It may move back and foward, but it may no longer be able to do that at the speed required for a smooth idle.

 

I do believe that is my problem.

 

S3 ICV wears out due to the brushes grinding holes into the armature,
use a pick to move the vane if it sticks at any part of its run then replace it.

S4 ISV is magnetic so no brushes to wear out,
BUT the shaft can become corroded from moisture intrusion and this will be very hard to detect,
maybe thats why spraying any type of lubricating oil into the system seems to make it work .

Otherwise use a pick to see if you can move the vane,
if its stiff replace the part even if it looks new on the outside.

a jumpy idle or a low or high idle could be indicators that it needs to be replaced

 

PorKen and MrMerlin I have read many of your great posts on the issue. The vane moves freely. In fact I was surprised how easily it moved. I will test tonight with current to see if the vane has some resistance.

The idle issue I'm still having is a erratic surging. It's constant up and down every 10-15 seconds. Hold throttle at 1200 it's fine, let off and it almost dies or does die.
I also found the the FPR vac line leaked fuel into the J channel on the throttle body.

 

Surging is frequently a vacuum issue.

 

NOTE if you smell any fuel in the vacuum lines then you have a compromised damper or FPR.
I suggest to replace all 3 of these parts

 

"Surging is frequently a vacuum issue."
I have replace all but the line going to the Trans. The last check is the ISV and replace the trans line.


"NOTE if you smell any fuel in the vacuum lines then you have a compromised damper or FPR.
I suggest to replace all 3 of these parts"
I smelled fuel the last time I was working on it and made a note to replace it. To my surprise yesterday when pulling everything apart I found that a bunch of fuel had drained through the line and to the J

I am working towards Kens chip, but need to sort some stuff out first. Can the FPR and dampers be upgraded to the '87 without the chip?

 

The S3 ISV has three pins, the center is ground, the other two are for Open and Close.

The LH pulses the open and close constantly to maintain an idle, placing a voltage on the corresponding pins will either open or close the ISV, usually with distinctive "clomp".

However this does not guarantee fine movement can be maintained. When in doubt, replace it and move on

note: a damaged ISV motor if left unchecked can damage the ISV Driver Transistors in the LH

Dave

 

note: a damaged ISV motor if left unchecked can damage the ISV Driver Transistors in the LH

WOW didnt know that!

Thanks for the info

 

If you consider that a bad motor will require the driver circuit to work harder to move it, that will eventually cause the circuit to fail due to stress.

I think that is what happened to the original LH n the 86.5 "The Onion", that LH works great when cold but when the LH ISV circuit heats up, it goes to 1500 RPM and stays there until the LH is stone cold.

 

I recall a thread with a pic of a S3/LH2.2 board where the 'close' transistor had gotten so hot it had fallen out of the board.


Pre-86.5 green board (vs. 86.5 yellow board)

 

The dampers for the S3 can be replaced no problem, however, I wouldn't want to run the car on an '87 FPR for long if you don't have the programming to properly adjust for the increased fuel pressure.

The FPR isn't hard to swap out at all. Just be careful with the bracket, it's thin and likes to move if pressure is applied. If the large nut (24mm?) won't budge then you'll need to take the FPR and bracket out together. Again, not very hard at all.

 

ack. I've had a creeping warm idle- definitely not over 1K but noticeable increase from baseline. Assumed it was a heat-exacerbated vacuum leak. Did you have to rebuild the LH, or trash it/replace, or what?
Frustrating, the ISV was an early R&R item to get a sound basline, it's nearly new. And is the S4 unit a drop-in? Don't recall, I might've even gone that route last time.