Crazy CIS Startup Idle.
 

My motor, (Which is a 79 3.0 with CIS) when cold, revs up to about 2500 rpm on startup and stays there. It's super loud. Then, if I drive around town for a mile or two, shut the car off, and come back to it in a few minutes, the idle is so low that it shuts off and stalls unless I keep my foot on the pedal.

Any suggestions from CIS gurus?

My first stop would be to check the part number for the AAR and see if it is correct for the engine.

Have you done anything to the system recently? Or did this just show up, if so, what was the last thing you did to the car?

It sounds like you have an internal leak through the AAR, AAV or Decel valve. The leak happens when cold (lean when cold and rich when hot), because one of those is hung up when cold, then when warm it closes. The system was probably adjusted to compensate for a partial closed device to idle well when warm at some point, now the device has changed its behavior and is going full closed changing you idle air mixture.

What happens if you continue to drive for more than a mile or two? Do the revs ever go down from 2500? Did this start w/ winter temps?

Like SOuk said. Did you do anything to the system recently or did it just happen.

In order of likelyhood:

- AAR
- Decel valve membrame pierced or AAV membrane pierced.

These two cause these sypmtoms.

IS your mix and dizz still at same position?

Michel

Yea, I haven't touched it...at all. It's possible that maybe the cold cracked a vaccum hose or something, perhaps.

Yes....as I said, the miles tend to make it idle TOO low. If it were a hose, what would I do to diagnose it?

My experience is that vacuum leaks get worse with heat and usually don't heal themselves. There are lots of possible vacuum leaks with CIS, injector sleeve O rings, injector seals, boots throttle shaft, hoses, pipe manifold behind airbox, airbox, etc. An unlit propane torch with a long hose is the best way I've found to find a leak.

Can you clarify this? What would I do with it?

Open up the propane torch (unlit) and carefully wand it around various places where unmetered air might enter the CIS, such as the intake runner boots, injector O-rings, etc. Should the idle speed of your engine pick up, you've identified the leak.

Good luck!

Brian

It might be vacuum leaks as others suggested but since you describe high rpm at start and then too low when warmed up can I suggest you check the decel valve. I have had the same symptoms last year and it was impossible to set the idle, too high cold to low warm. Sometimes it was spot on when warm until I stopped again and hup down it went.

You can chekc the decel valve with everything in place, simply bypass it by connecting the two large hoses that go in and out to each other, also block the small hose that goes on the T connection to the thermo time valve (possible you do not have this) and then to the WUR. WHen you have bypassed it and blocked the T and your Idle is back on you have a faulty decel valve. It is not a serviceable item.
THe AAV (not AAR) can cause the same symptoms but it is very hard to reach and thus the above is diffcult to perform, but I doubt that one is kaput as it performs under far less stressfull circumtances....but lets assume nothing.

Let us know.

Michel

Wow..that's like...mystical or something. :)

Thanks!

Can you clarify this? What would I do with it?

Hold the hose next to the likely leak sources and listen for a change in idle speed. It may increase or decrease depending on the mixture, but the change will be obvious. Much more effective than spraying liquids and you do not have to worrry about dissolving rubber or plastics. Virtually all SC's leak at the injector sleeves because of the poor seal design. Vacuum leaks usually get worse with heat, and I would also try to isolate the AAV and the decel valve.

Possible AAR, AAV, Decel.Valve malfunction and air leaks as others have suggested.

I would check the AAR first because it's relatively easy:

The AAR is located on the right side of the engine between 5-6 intake runner.
It's the item that has a small electric plug and a large vacuum hose connected to it.
With engine cold, open the clamp holding the outside-hose.
Pry it off with the screwdriver just enough to get it out of the way so you can see into the opening.
Don’t worry about the Alu pipe; it’ll move enough.
With the help of a small mirror and a light, peek inside the AAR.
When COLD, you should see an opening in the slide shaped like a half-moon.
When HOT, the opening is completely closed.
If it isn't closed when hot, the AAR is either kaput or doesn't get any power.
You can spray some WD-40 into the valve in case it is just sticky.
To check the power, carefully open the tiny clip on the plug with a very small screwdriver and pull it off.
The wire clip is tricky but necessary; don't yank it off.
Start the engine and check the plug for 12 V.
(One wire is power, the other (brown) is ground)
If all is well, replace the hose and clamp securely.
Let us know if the AAR works HOT and COLD.

AAR Bosch 0 280 140 209 for '78-'79.

Ok...good advice. I'll give that a shot.