Vacuum lines and idle control fix

I've been hunting down an intermittent idle issue on TheHoff since our last Brand Hatch excursion - which led not only to testing & replacing parts but also eliminating others and making one completely from scratch!

As the Idle Control Valve (ICV or ISV) was the suspected culprit the whole intake manifold, throttle body, AFM and filter had to come out - oh and the fuel rail too. Actually it's less of a phaff than it sounds.

As ICV's are around £150 to replace I wanted to test mine to be sure it was faulty. After removing it from the underside of the intake manifold I jumpered it directly to the battery and it works perfectly with a very solid "clunk" when activated and deactivated. So that wasn't the issue.

I also made sure that the hoses running from the ICV to the intake and the J-Boot were correct also as I suspected I may have routed them incorrectly - turns out that was also correct according to how I had fitted the ICV.

So what ever was causing the intermittent hunting and low idle speed wasn't anything to do with the ICV. I decide then to try to reduce the mass of vacuum hoses and connectors under the intake to reduce the chances of leaks.

While the intake was off I also cleaned up all the connectors for the sensors and replaced the temperature gauge sensor with a £5 one listed for Land Rover called ERR2081 - thanks to Waylander on Tipec. This was to cure the temp gauge jumping.

After doing some research on deleting the Venturi and simplifying the vacuum hose setup I reinstalled everything except the Venturi which is the grey y-tube in the right of the picture below, deciding instead to connect the ICV hose directly to the J-Boot, and the other to the front of the intake to make a closed ICV loop.

The result of turfing the Venturi and small check valve (which is inserted in one of the rubber hoses) was that the engine idled at about 2000rpm and slowly increased! Not a good thing...back to square one.

After some more forum thread reading I decided to refit the Venturi but not connect it to the ICV but rather blank the one connector as seen below:

Now the Venturi is connected to the rear of the intake via a short rubber hose and directly to the brake booster - no check valve. The result is the car idles as I hoped and there are fewer hoses to clutter the engine bay & go awry. Result.

What I also discovered when inspecting the engine when the intake was off was that there appeared to be oil leaking from the dip stick tube where it enters the engine block. The problem it transpired was that the dip stick tube mounting plate which attaches it to the rear of the intake manifold is positioned about 3mm too low, consequently the tube doesn't seal correctly with the block & o-ring when affixed with the bolt. The fix was to drill out the top of the mounting plate elongating the slot so that the tube could be pushed further down into the block. Once tightened up with a bolt it sat sealed in the block nice 'n tight.

During my "research" looking at vacuum hose diagrams and threads I'd come to the conclusion that the thin hose running from the check valve at the brake booster firewall had been routed to the incorrect point in the intake assembly. It needed to run straight to the side of the S2 manifold - a point that had no barb connector - well not since it had been powder coated. Looking back at old photo's that connector had been there with a short piece of hose but obviously the powder coater had removed it - which is why I had plugged it with silicon upon finding a hole. The problem now was how to refit a new barb?

I bought a couple of hose take off's from Revotec in the hopes that I could use one of them but in the end I figured that if the original one had been removed by pulling it out the chances were that the I could extract one from the S intake that I had laying about in the garage.

A twist of the vice grips was all it needed and it came free. I connected it to the hose and then covered it with Porsche's favourite Loctite 574 and inserted it into the S2 intake after removing the silicon plug.

Should this fail I'll need to remove the manifold and drill out the hole to enable the fitting of the nice Revotec hose take off that I now have in my small parts stash.

With that all done and running ok the time had come to make a custom intake J-boot to fit between the AFM and throttle body - coming up next!