UKKid35

My automatic assumption was that it was the ISV, so a couple of years ago I sprayed some Carb Cleaner in the relevant hose, left it overnight, and it was fixed.

However some months ago the issue returned and the Carb Cleaner trick didn't work.

My next thought was that the MAF was out, so I sent it to JDS for calibration and it was returned as is after it checked to be out by only 0.9% and thus within tolerance.

Next I replaced the Temp II sensor, no change.

So I resigned myself to pulling the intake and cleaning the ISV properly. What I mare that job is, I'd forgotten how awkward it is to remove various hoses and connectors, but at least my decision to leave the metal clip off the ISV connector many years ago paid dividends.

Imagine my disappointment when I connected the ISV up to a 12v supply and found that it was completely fine, not the slightest sign of being slowed, let alone seized. I've now cleaned it thoroughly so it's nice and shiny inside, but it was just as quick before I cleaned it.

What do I need to do next before putting it all back together (apart from replacing the plastic elbows that cracked as I took it apart)?

There were no obvious signs of vacuum leaks, all hoses seemed intact, and cable ties were used to seal the plastic elbows to the rubber MAF elbow.

I haven't yet checked the Throttle Position Switch - could that be the culprit?

Any chance it could be a weird LH failure?

I am at a loss, any suggestions welcome.

FredR

I have a similar problem at idle and I am pretty sure it is the ISV that is now 27 years old. You might be able to see it move etc by applying voltage but that is not a real world simulation of how it works in practice or so I belieive.

In my case I intend to pull the inlet manifold next project season and replace the knock sensors [connectors falling to pieces], the Hall trigger and the ISV. I do not like changing things speculatively but sometimes there is no alternative. Porsche told me mine was bugggered about 16 years ago- I pullled the thing, cleaned the shuttle thoroughly and it has done me to date but any kit like this that has moving parts and motors has a finite life.

Rgds

Fred

MainePorsche

Assuming by your avatar is a MY 87.
Is it an auto transmission ?

UKKid35

Manual, Non-Cat, Open Loop

UKKid35

Just checked the TPS and it only closes on WOT, nothing across the other pins on idle, so presumably this means the ISV never operates.

Hopefully that will be it, will report back in due course.

UKKid35

I run without the clip too, can't imagine how the connector could come off though -It's hard enough getting the connector off even without the clip!

FredR

Just make sure you are checking the correct pin assignments. The closed switch is a micro switch type device and generally very reliable unlike the full throttle thingy that dates back to the Victorian era.

If the ISV is not working at all then it should not be hunting. You need to determine if the idle contact circuit is open or closed - if the brains think the motor is at idle the ISV will drive closed when running, if the brains think it is running the ISV will never operate.

granprixweiss928

Grounds all good? Esp under the airbox. Perhaps Crank position sensor or Hall sensor? have those been looked at?

UKKid35

I wish I'd replaced the CPS last time I took the clutch pack off. I seriously doubt there's any chance I could get the CPS out non-destructively. I would have to remove the flywheel and knock it through.

UKKid35

Found a use for the air pump filter housing at last

MainePorsche

The grounds under the air box at the back to the 'V' bolt to the block via the throttle cable pulley bracket bolts. They ground the ezk, lh, and ignition harness. This is mission critical to service it.

UKKid35

Thanks, will clean them up, much appreciated.

UKKid35

Done - many thanks.

I'm careful about vacuum leaks too, so I cable tie the elbows in the MAF sleeve.



(Sorry about the giant pic)

I spent a very uncomfortable hour or so searching for one of the ten plenum mounting sleeves. I lifted the plenum again to check it wasn't in one of the intake ports. Finally I found it safely in a parts box - Celebration time!!!

Plenum now bolted down, with only throttle cable, MAF, and fuel rails left to go (and some vacuum tubing too).

I was very lucky that I found myself reading Dwayne's write up earlier, because it reminded me that I do have a Mityvac, and that I really need to check the flappy operation. Good thing too because not only was the vacuum line leaking, but I'd forgotten to fit the actuator arm!

UKKid35

Now it's all back together again I have discovered the following:

I cannot remember the last time I heard the TPS click, it must be years (since the TPS actually worked properly)

The engine has vacuum leaks around the brake booster Y piece. In particular the O ring seems to be at fault. I am trying a similar size O ring that is meant to be for AC applications, will see how that works

The Coolant System Pressure Switch is less water tight than a sieve

The Coolant Bridge to Expansion tank hose clip isn't doing much at all

I think my 12 year old Anchor Engine Mounts (costing $20 each) are now starting to suffer

But on the plus side:

The engine now returns to steadyish idle from blipping the throttle very nicely, that must be the ISV doing its thing

I count this as Total Success - as I haven't dropped anything down one of the intake ports causing total engine failure (similar to my Ring trips - I've won if I get to drive home afterwards)

FredR

What was that famous line on Apollo 13? - "... Let's start with what is actually working".

The system should idle when warm with the ISV in its rest position doing squat. Such circumstance is characterised by the need to work the throttle under cold starts.