F451

I sprayed WD40 a few times after the carb cleaner spray downs thinking it would flush the carb cleaner and possibly lubricate the ICV. Once I was satisfied that the idle was steady and the ICV seemed to be functioning normally, I gave it a final shot of WD40 and called it good.

jchasty

Thanks!

chart928s4

Those are the exact symptoms of my failed TPS. It also can be caused by all the other things Stan mentioned.

I found that an intake refresh not long after I first got the car was well worth the trouble. It's expensive and DIY will take a day or two, but once it's done you will be free of most fiddly problems for the lifetime of your ownership. You will drive yourself crazy with little fixes. ×

jchasty

So, I know I'm going to regret writing this, but had a run out this morning and apart from one episode of hesitation when part warm, it behaved perfectly!

I will continue to cycle of carb cleaner, sit, start, WD40 and drive for the next few days....can't find an icon for "fingers crossed!"

jchasty

OK, more weirdness....was about to write and say after a 30 minute drive that I was going to declare success! Returned home with a rick solid idle at exactly 750 rpm. The idle has never been so steady.

I switched off to re-engage the rear wiper (another one on the list) and after 5 minutes decided to put the car away.

Would it idle? No! More bunny hopping into the garage.

Pulled the pipe - more carb cleaner / WD40 - now runs sweet!

What on Earth? The only difference between inside the garage and outside is a slight incline - would that have anything to do with it?

Thanks in advance!

John

FredR

John,

Nothing to do with the incline unless your driveway is on the edge of Lulworth Cove!

What folks often do not seem to understand is that a malfunctioning ISV is infinitely worse that one that does not work at all. The ISV has a default aperture that when warm passes enough air to support an idle [with no ac] and my experience is that it works rather well to the point that one would hardly know it was not working until a cold start is needed then one has to work the throttle some and in cold European winters maybe totally impossible to start but of course I do not have that particular problem to contend with.

Now, once the ISV is working, the shuttle is positioned via a stepper motor with the computer trying to apply a feedback control loop to modulate engine speed at 675 rpm assuming the idle speed contact is telling the computer the engine is at idle. If the shuttle is sticking then the control algorithm goes down the toilet and when nothing happens the controller says "Giddyup" so adds more of the control variable, eventually the stiction breaks and then too much air is allowed, the engine tries to race and the computer now says "crap- put the brakes on quick" and the system goes unstable. When the engine is on the verge of stalling out presumably it cannot pick up as normal and you get what you got. You latest episode pretty much confirms this.

When this happened on my late S4 some 18 years ago the local agents initially told me the ISV was shot. I thought "sod that" and did my first inlet manifold job with the ISV the main target at the time. When I got the inlet manifold off I found a surprising amount of oil in it but the ISV port was bone dry. The shuttle inside the ISV was almost unmovable and was covered in a greyish powder. I managed to get this stuff out with a toothbrush and patience. Then I squirted a little WD40 onto the shuttle and it then turned with little resistance. That ISV is in my spare parts bin having been replaced pre-emptively last time i had the manifold off a couple of years ago- it still works.

Now, whatever crud is troubling your ISV clearly has not completely gone but for sure it is causing your issue. I stated earlier that I am not over enthused about squirting large amounts of WD40 down there but I said even less about squirting carb cleaner. Just remember anything that can get rid of carbon can also get rid of a whole lot more of less troublesome components such as petrol and perhaps of more concern- lube oil. As Stan said, hoses may well suffer longer term. I cannot tell you it will cause damage of any kind but the potential for creating problems would concern me. That carb cleaner stuff is brutal and I trust you are wearing eye protection when using it. The stuff is designed to work with kit designed to handle petrol such as carburettors so should be OK downstream of the injectors but upstream? The stuff is going to hit rubber hoses at the ISV and also breather pipes so do be mindful of such. Just to add insult to injury the primary component in the stuff is ethyl benzene which is also classed as being carcinogenic

jchasty

Thanks Fred - will give up the carb cleaner!

Bottom line, do I need a new ISV? It's driving me insane!

FredR

John,

The beauty of what you are doing is it is a simple approach- it either works or it does not and as long as there is no secondary consequence nothing lost in trying. Once you go down the inlet manifold removal route there are a pile of potential "while you are in there" items conditional on the history. In the case of the ISV the question then becomes one of would you want to clean it, test it to the extent possible and put it back knowing it might be useless or would you put a new one in there? I chose to put a new one in- the Lowe aftermarket unit- has worked OK to date and they are very reasonably priced. For me taking the inlet manifold off and putting it back on is not such a big deal have done such in a good afternoon's work. Doing it in 40C heat is another matter altogether [BTDT as well] but you do not have that problem.

FredR

Not so fast- maybe it will kill the Covid virus?

jchasty

Thanks Fred

I don't have the heat, but I also don't have the skills! I've found the Lowe unit on eBay, but the process looks daunting!

jchasty

It's going into the Porsche dealership tomorrow for their Classic Tech to have a look (it's literally 60 seconds from my house). Be interesting to understand their fault-finding process.....

chart928s4

At least 7 possible causes of your problem are equally likely. The Porsche Classic guy should have a Bosch Hammer diagnostic tool - suggest you ask explicitly. If he doesn't have one he'll be guessing also. ×

jchasty

Hiya, yes they have one. I dropped it off this morning and he has all day to fault find. I took it for a drive first and it was perfect!

FredR

For those of us with excellent deductive reasoning skills when actions taken modulate the problem- be it for better or worse, that generally is a reasonable indication that one has found the root cause of the problem especially when initial diagnosis of reported symptoms suggested the same thing. Then again maybe we were "just lucky".

If the chap looking at your 928 knows his onions do not be too surprised if he finds other issues- as I recall this example is new to you and the notion that your PO did everything that needed doing does not follow the established paradigm with these cars. Then again you might just "be lucky".

jchasty

LOL! I'm preparing for the £££Shock.....