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"hunting"

The sensing of the rpm and crank position is not that accurate, so some amount of hunting is normal with an electronic ignition control, no matter which ecu. As the sensors and other companonts age, it gets more noticable.

My warm idle does something similar. It drops a bit, then recovers immediately. Best explanation I found was the CPS (crank position sensor), and if it really bothered me, I could replace it now, before it fails... sometime in the next 50-100k miles... (NOT!) That makes sense, because I think the CPS is a Hall-effect sensor.

In theory the output from the sensor is a 5V square wave. In reality the signal is noisy. A clean waveform depends on an effect called "hysteresis", which filters out some of the noise but creates jitter in the waveform.

In other words, the sensor translates mechanical rotation into an electrical signal. Mechanical vibration in the shaft is converted to electrical noise by the sensor. That noise is filtered to obtain a clean signal. The filtering causes some inaccuracy called jitter. If that signal is used as one of the inputs to correct the timing, firing angle etc., you get some variation in rpm around the correct speed... a.k.a. "hunting". You can see it plainly on the graph...

Btw, thanks for posting that, I wish I had one of the cold idle on my car... :cheesy:
 

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What did you use to reglue the nipple seals? Looks like epoxy to me, but I am not really sure what it is.

Mine are solid so far, but some of the reddish color glue was cracking and coming off. Cleaning some of the crud did not help. I have a spare tb for another reason (the sticky throttle lever), but have not put it on yet and the seals are about the same. Did you take a look inside the two chambers on the underside of the tb? The one where the pcv line goes was coated with almost 1/8 inch of black oily crud, and the replacement was not much better when I first got it.

Speaking of the evap purge line, on the turbo that can cause some idle issues if not working correctly. Not sure on the n/a version. On the turbo, the ecu waits until the engine is warmed up, then it starts to cycle the purge valve (tapping sound you can hear at warm idle when you put your ear next to the fender). The reason for allowing only short pulses on the purge valve is to avoid screwing up the air/fuel mix with the fumes from the charcoal canister. If the purge valve does not work correctly, opening and closing when it is supposed to, you get idle problems and poor mileage at low speeds.

(A cracked evap purge hose does not help either.)
 

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Slaab4life said:
...I wonder why it was found to be necessary to add these sacrificial pieces. The main portions of the line appear to be of the same material (and theirs plenty of length to them that I have them looped). Another Saab mystery I guess.
I was told those hoses have to be treated the same as a fuel line, because they carry combustible vapors. If need be, they should be replaced with reinforced fuel line, not rubber hose. So, the reinforcing pieces may be there to keep the hose stiff enough so the ends can be clamped harder. Mine has some mutant crimped clamps.

I don't like that evap system very much. That hose had an encounter with a pulley during one of my unfortunate pulley and belt incidents. When the belt broke and knocked the hose loose from the plastic clip, the looped portion dropped down and made contact with the pulley. Not good for much anyway, the activated charcoal does not last more than a few years w/o being reprocessed.
 

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tidewatersaab said:
the charcoal canister probably costs more than it's worth to replace,right?
p/n 4445821, $35 at saabsite.com, probably the cheapest part of the system, but I would say none of this is worth spending money on unless you need it to make the CEL go away and pass emissions.

Getting the engine to run well w/o fouled plugs or O2 sensors and improving the mpg would do a lot more for the environment in the long run. New plugs, injector cleaner, and cleaning the crud out of the IAC and TB usually improves my mileage about 10%. That 10% difference in mileage translates into a much larger difference in emissions, because fuel is burned more efficiently all the time. Compared to that, the evap system and SAI together are negligeable, and much more expensive to repair.

Imagine what would happen if everyone in the country did a tune up over Memorial Day... next week, nation-wide gas consumption would drop 10%, and so would the price of gas :cheesy: ... makes you think, doesn't it?
 
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