Inline-4 vacuum question

[Californio]

Hey folks,

I'm trying to sleuth out a wonky idle on a Tiico conversion, starting with the vacuum. Some questions:

1. Only the "metered air" between the throttle body butterfly and the manifold makes a difference, right? Anything else might affect emissions, etc. but not the idle.
2. The places a leak can start are: throttle body butterfly valve hole, brake assist hose, fuel pressure regulator/decoupler hoses, surface between throttle body and manifold, and map sensor fitting. Anything else farther "down," closer to the block?
3. I tested the brake assist and it held vacuum 15 lbs. for about 20 minutes. That's good enough, right?
4. If I were to squeeze off the fuel pressure regulator hose to test for vacuum leakage, the engine would run rich, I think. How do you test for vacuum problems without disconnecting the FP regulator?

thanks all!

[Vanagon Nut]

I don't know the Tiico but am familiar with the ABA Motronic. Your engine likely has an ISV and associated plumbing to-from it. A leak at the hose connecting the outlet of the ISV could affect idle.

And I think, a leak at the intake boot could affect the hot wire in the MAF. But as you suggest, this may only affect the mix.

Does the Tiico have an OBD port?

The ISV can get dirty. Running carb or throttle body cleaner through it may help. Do NOT use brake cleaner.

Some use a propane torch to check for leaks. I haven't tried this method but I'm sure there's info hear on that trick.

Neil.
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1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN

[Californio]

Yes, the Tiico uses OBD-1. They're notorious for throwing codes that don't mean much, as the O2 sensor system isn't what the Motronic ECU was designed for.

I don't think there's any ISV on these, though the symptoms described here http://forums.vwvortex.com/showthread.php?2894334 are exactly what I'm seeing. Perhaps internal to the throttle body (which is from a 1990's Jetta.)

I'm going to try running it without the intake boot connected, see if that makes a difference. Also will try the propane trick.

Those old boxers sure are nice and simple.

[denwood]

I had a similar issue with my i4 conversion, albeit Digifant II ...wonky idle and CO setting that could not be done properly. Right now, it starts well at all temps, and idles rock solid. I was able to finally set up the MAF sensor spring tension correctly for correct mix at full throttle and cruise as well.

The method that finally worked well for me was propane. Using a standard propane bottle, ( http://www.canadiantire.ca/AST/browse/6/Tools/Weld...locale=en) remove the burner tip and replace with a plastic hose, a few feet long. Start the engine and while idling, open up the propane valve a bit and run the tube along all parts of the intake, each injector seal, ISV if present, oil filler tube, PCV valve etc. If the idle increases at one point, you've found your leak.

My issue was that all four injector seals were installed improperly...and all were leaking.
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Cheers,
Dennis Wood
The Grape

[Vanagon Nut]