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Since it's an 8V, the culprit might be >
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Posted by Micah in NC [Email] (more from Micah in NC) on Wed, 21 Jan 2004 15:35:22 Share Post by Email
In Reply to: Re: Patrick, what model 900 is your '87? Base 900? >, PatrickB, Wed, 21 Jan 2004 11:52:30
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any one of several things.

My '84S would stall and sputter when in the warmup period. It also didn't have a high cold idle speed. 8-valves SHOULD idle high when first started for five minutes or so if engine has been sitting for several hours or more. The idle should gradually decrease during those five minutes.

The problem with my '84 turned out to be the AAV (Auxilliary Air Valve), as mine was stuck closed. These are fairly easy to check out, though. I have instructions and photos for doing so on my fledgling website. I'll link it below.

If this is not the problem, I can also suggest looking at the thermo-switch for the fuel injection system. If the 40-55°F stalling problem has been persistent the WHOLE time you've owned this car, then keep reading. If the idling problem just cropped up, it should NOT be this thermo-switch's fault and I'm out of ideas.

The thermo-switch on your '87 should be at the intake manifold, between cylinders #2&3. Switch has two wires leading to it. In some cars, the wires were colored yellow/red for one wire, black for the other wire. Try a cold start with these wires disconnected from the thermo-switch and jumped (connected) together--do this BEFORE starting.

This will directly allow the deceleration relay--which during warm-up period assumes the role of a "warm-up relay" of sorts--to lock the Lambda valve (buzzing valve on driver's side inner fender) at 60% modulation. This means the Lambda valve is open and sending fuel to the engine 60% of the time, instead of "listening" for oxygen sensor output. This scenario is, in effect, the 8-valve's equivalent of the 16-valve's air mass meter.

That last statement means that the 60% Lambda modulation "lock" provides the approximate amount of fuel the engine needs when cold. It also prevents the CIS fuel injection computer from using the signal supplied by the oxygen sensor. Why? Well, you DON'T want the CIS computer trying to "listen" to the oxygen sensor signal too early. If it's very early after startup, there isn't any signal at all from the O2 sensor. The O2 sensor only begins making voltage AFTER it gets heated by the exhaust for a few minutes--a "heat battery" as it were. (This voltage is what the CIS computer "listens" to in order to tell the frequency valve how long to remain open). Voltage swings up and down in a range from 0 volts to 1 volt when O2 sensor is working correctly. The lower the voltage, the leaner the mixture, and the longer the Lambda valve is then instructed to stay open.

Thus, the O2 sensor is sometimes called a "Lambda" sensor.

That thermo-switch determines when and for how long the decel relay does it's "warm-up relay" act. The thermo-switch grounds the relay's pin X1 and provides the 60% modulation lock (where O2 sensor is ignored) until coolant temperature reaches about 77°F. This is why I suggested--as others have done in ages past--to jumper the two wires together, thus making the CIS "ignore" the O2 sensor input. And it will do this until you up-jumper them.

NOTE: If this makes no sense, don't feel bad. It took me years to get this far, and I'm no authority on CIS injection by any means. I hope I haven't left any key points out!!!

For more info on the thermo-switch, see the posts referenced in my old TSN post here (copy & paste this URL):
http://www.saabnet.com/tsn/bb/900/index.html?bID=244842

Also, see this excellent post by Kevin K: http://www.saabnet.com/tsn/bb/900/index.html?bID=136217

Hope this helps! Keep us posted on any results/questions you come across.

Micah in NC
'84 900S, 250K mi.

posted by 66.20.173...

Click here for my page on the AAV.

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