'79 CA FI idles at 900rpm drops to 700 every 10 seconds w/hiss

[busdaddy]

The fan smoke sounds like oil burning off from the heat exchangers, and non functional anti return flaps.

The idle issue is odd, what happens when you unplug the oxygen sensor?
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[Tcash]

Build yourself a smoke tester and smoke test for vacuum leaks.
Finding vacuum leaks with smoke (smoke test, tester)

Pull the distributor cap and look for carbon tracks.

Ignition High Tension Leaks

Cylinder power balance (contribution) test

Hook up a fuel gauge and see if there is any fluctuation when the fault occurs.
Testing FI Fuel Pressure FAQ
Fuel Injection Fuel Pressure Testing

Could be a sticky injector.
Fuel Injection Leak Down Test

Good luck
Tcash

[Tcash]

Did you get the timing light to light consistently? Qualify the light on another vehicle. If it passes. There is an ignition problem.

[thebayfromak]

[Tcash]

Wonder if it is a sticky valve. Run a Vacuum test on it.

Code:
Vacuum gauge

Go down to the bottom of the page and Look at Scenario 5
http://www.secondchancegarage.com/public/186.cfm

Good luck
Tcash

[SGKent]

I want to say that Vanagon Fi had a problem like this and they added an idle stabilizer to stop it. The FI system you put on it, was it from a 1979 Bay or from a 1980 Vanagon?

Also - I recall that if the PCV valve is bad and the engine a little rich it can cause this. The case builds up a vacuum as the engine goes lean (increasing the RPM), then the case reaches a vacuum stability, the mixture goes rich again and the RPM falls, the case sucks in more air and the mixture goes super rich. Eventually the case stabilizes at ambient air pressure and the mixture goes lean again, the cycle continuing. So check the PCV valve. They are NLA. The small hole in the top should hold a vacuum. Do not clean the inside or they dissolve.
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[Randy in Maine]

You should not have an idle stabilizer or a EGR valve hooked up (capped would be OK). I like to keep the by pass air adjustment in the middle of its range myself. It gives you someplace to go.

It would be good to have a look at the aux air regulator to be sure it is not somehow leaking vacuum at the 90º little boot or where that stuff plugs into the S boot.

Are the injector seals all nice and new (big ones and little ones)?

Are you running the correct 79CA AFM and 13 plug double relay? You have to.

[thebayfromak]

[SGKent]

where does the other end of that breather hose go?
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[thebayfromak]

[SGKent]

that is likely your issue, or one of them. The case acts like a huge vacuum storage chamber. The engine first pulls air from it to create the same vacuum as the S-boot. That causes the flap in the AFM to open less. Then when the vacuum is established in the case the flap opens more changing the mixture. The RPM drops and air rushes back into the case opening the AFM flap more and richening the mixture. Then the cycle repeats. You need a working PCV valve. For now, (it won't get you past smog), let the breather dump under the bus away from heat and the exhaust, and plug the S-boot portion. The PCV are very NLA. A good one will hold a vacuum in the small hole on top. If it doesn't hold a vacuum then it is no good until someone makes new diaphragms for them.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[Randy in Maine]

Build one of those paint can smoke generators. It is cheap to do and it is helpful.

Sometimes you have to ply with things cheat a little to get vacuum leaks in control. Take the power brake booster out of the loop by putting some duct tape on the vacuum hose. A couple wraps of electrical tape and a zip tie can ensure there is not a lot of leakage at anything attached to the S tube. You could take each of those plugs in out of the loop with some duct tape. Make sure the throttle body seal is nice and equally tightened. Put a golf T in the EEC valve that goes to the air cleaner. See if the timing jumps from 5º ATDC to about 7.5º BTDC as you remove and reattach the vacuum line to the retard.

Do those things one a time and see if anything changes. Report back your findings.

[telford dorr]

Put a fuel pressure gauge on the test tee, and see if the fuel pressure fluctuates during the slowdowns.

Borrow an LM2 exhaust gauge, clamp it onto the muffler tip, and see of the readings change during the slowdowns.
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