1978 FI High idle - vacuum leak? SOLVED!

[Bayerleiner]

I have a 1978 Champagne II edition beetle convertible that suffers from a high idle when warm that can't be adjusted by the idle adjustment screw or ignition timing (when cold I can get it to idle around 900 RPM with the idle screw fully seated)
I have diagnosed this as a vacuum leak so today I tried making myself a smoke machine to find the leaks. I found three leaks:

1. a leaking intake manifold sleeve on one side (In this area I also got a reaction when spraying carb cleaner so this obviously has an effect). I will change this sleeve to get rid of this leak. (I will also replace the cracked injector seals even though no smoke came out there.

2. a lot of smoke also came out from under the oil filler cap. I have read in some posts that this is also a vacuum leak since the breather hose goes straight to the intake after the AFM. Is this so? In that case I probably need a new gasket for the oil filler cap.

3. A huge amount of smoke came out from behind the crankshaft pulley. When i removed the pulley I saw that the smoke came out from behind the oil deflector plate on the end of the crankshaft. Is there supposed to be any sealing ring or something there or what do I do with this leak?

[Dwayne1m]

1) Yes replace the injector seals, and I would also suggest to replace those short fuel lines that feed the injectors while you have the manifold on the workbench. Much easier to replace them on the bench instead of in the car.

2) There is a hose that goes from the oil filler neck to the "S" boot. It shouldn't leak around the oil fill cap. There should be a rubber gasket in the cap. Good luck finding one.

3) There is no seal at the crank pulley. That's not a "leak". The smoke has to come out somewhere. That is not a problem.

Personally, I found it easier to just use carb spray to find leaks. I didn't have much luck with a smoke machine. If your injectors seals are cracked it would probably be best to replace them on all injectors. I just removed my injectors and after only 2 years the lower seals were cracked significantly.

[busdaddy]

Is this a California model?, or the Federal (49 states) system?, some have a vacuum regulator on the air cleaner for PCV, if it's diaphragm is ruptured it'll be pulling full vacuum on the crankcase instead of a slow bleed.
Or does your crankcase breather hose go to the underside of the aircleaner directly?
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[Dwayne1m]

[busdaddy]

Most are like that, but there are a few that have the bonus valve and pull off the plenum, not sure why.
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[VW_Jimbo]

The vacuum leak within the case may be from the seal being lost inside that area. There is a nut on the interior which bolts down onto the same four studs that would hold on an alternator stand. That one leak only shows a very weak sign of itself, at the oil filler cap. A complete reseal of the intake plenum is required. Sorry man. Good news is everything will be resealed and should be able to withstand the vacuum.
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Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[Bayerleiner]

[VW_Jimbo]

That’s it!

I use Gasgacinch and a paper gasket.
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Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[Dwayne1m]

Do NOT use any kind of gasket in a tube. Get some paper gasket material and use that. You'll have to make your own. Not a hard job. I used gasket in a tube for the plenum half once. Lasted a few months before the gas ate it away. Major vacuum leak developed. Then made my own gasket and worked great.

Something else to consider, since you have the engine out and you're this far, give it some thought to taking your alternator to a shop to test. It would suck to assume it's in good shape now only to have it give you problems down the road and you'd have to do this all over again. In the pic I'm pointing to the little bolt that has to be removed to get the alternator out. You can't get to that bolt unless you remove the shroud or split the plenum.

[Bayerleiner]

I finally solved the high idle and thought I'd share the solution since I couldn't find this solution while searching, maybe because you normally don't touch the throttle plate stop screw.

I sealed every vacuum leak in the engine, and put it back in. I was not very happy when I found that the idle still was too high with a warm engine. I could not adjust the ignition timing properly and when setting it to 30 +-2 degrees at full mechanical advance I got an idle of around 1300 RPM with the idle screw fully in when reinstalling the vacuum hoses.

But then I noticed that at 900 RPM I had vacuum in both the advance and the retard hose, so I thought that the throttle plate got stuck in an open position somehow, and it did. Somebody had been messing with the stop screw of the throttle plate so it was slightly open all the time. I set the throttle plate stop screw so that I achieved around 900 RPM with correct ignition timing and the idle screw 3 turns out and now the engine runs like a fuel injected engine should! (Like a dream, that is)

So to summarize: a high idle could be caused by the throttle plate stop screw, but first sort out all the other stuff like setting valves, making sure that there are no vacuum leaks and that the distributor and ignition system is ok.
I guess some PO of my car found the stop screw to be a good way to cure a low idle...

[busdaddy]

Nice work!, thanks for the follow up.
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[prolewicz]

With the alternator in place, how do you remove the plenum nut towards the front of the car. The alternator blocks the use of a socket and the clearance is too tight for an open ended wrench.

Thanks, Pete