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  #1  
Old 13th April 2011
pepper pepper is offline
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Thumbs down erratic idle, engine surges, etc in a 89 saab 900s

So i bought my dream car, an 89 900 about a week ago. I bought it because it started and ran well, and regardless of some problems (oil leak and no power steering) I wanted to turn this into the car I learn how to fix. Well lucky me cuz now I get the chance BIG TIME (just kidding, Im pissed) For the past 2 days the car very suddenly started idling very erratically, seeming like it might die at stop signs, then alternately lurching like the brakes cant hold it back. When driving from a braked position the car sounds like a golf cart, sputtering and hard to speed up quick. As for the rpms, it idles a bit over 1000, and sometimes the needle doesnt work, but is never much over 3000, even when going up to 50, from about 35 mph up it runs a little loud, but no more lurching or stumbling. Since this problem the check engine light has never come on, but the shift up light comes on intermittantly. Ok, so from this I'm sure you can see I am no car expert. I understand I should first check the vacuum hoses, then what steps and what order do I take them?

Is this car safe to drive short distances until it can be fixed?

Ummm the car's an automatic trans, has a pretty substantial oil leak... One thing that I was wondering, is there an issue that sounds like this that the guy that sold me the car couldve concealed until I drove the car ~75 miles, only to have it show up again later, or is it a coincidence that it drove. great and broke a few days later? Ie he quick fixed it? I thought if that was the case it might be a diagnostic clue?!! Im trying to be a gumshoe here, any info would be ever so greatly appreciated!!!

Last edited by pepper; 13th April 2011 at 06:41 PM.
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  #2  
Old 14th April 2011
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Vac hoses, as you say. A major leak somewhere. How are your plugs, wires, cap, rotor, air filter? Check 'em all. Clean the throttle body inside and out. Cable could be gummed up on the outside. Inside could be fouled as well - get some throttle body cleaner and follow the directions. Keep reading threads on here about high idle and running roughly to get additional tips.
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Old 14th April 2011
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It sounds like a vacuum leak to me. One technique is to systematicaly pinch off vacuum lines with your fingers. When you pinch the one that's leaking your idle will change, usually back to normal.

Check the electrical connections to the AMM, AIC, and NTC sensor. I use electronic tuner cleaner (spray) or you can just unplug / plug in and wiggle a couple of times to make sure everthing is making contact.

I always change plugs, rotor, cap, spark wires, filters, and set timing on used cars I buy. Unless there's a compelling reason not to, like a meticulous previous owner. But the sudden onset of the problems sounds like a vacuum leak i.e. hose off.
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Old 16th April 2011
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good to hear that it is probably something simple. I'll check the hoses and electrical contacts and let yall know if that's the cause. If not, or I guess even if so, is the car safe to drive for short distances? Thanks again!
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Old 16th April 2011
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also, whats with the shift up light?
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Old 16th April 2011
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Also put some methyl hydrate in your fuel bad fuel is........bad.
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Old 16th April 2011
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Quote:
Originally Posted by pepper View Post
also, whats with the shift up light?
By this I assume that you are asking why it is there in the first place? It's there because back in the day the EPA gave manufacturers a better fuel economy rating if they put the shift light in the car. (They may still?)

It is a simple indicator of engine RPM and vacuum. If you are above a certain RPM and the throttle is depressed it should light. There are more inputs than that to avoid nuisance indications. (For instance, it will not light in 5th.)
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Old 16th April 2011
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Quote:
Originally Posted by eggsngrits View Post
By this I assume that you are asking why it is there in the first place? It's there because back in the day the EPA gave manufacturers a better fuel economy rating if they put the shift light in the car. (They may still?)

It is a simple indicator of engine RPM and vacuum. If you are above a certain RPM and the throttle is depressed it should light. There are more inputs than that to avoid nuisance indications. (For instance, it will not light in 5th.)
His definitely won't light in 5th cuz he only has 3 gears.
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Old 16th April 2011
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by whats with the shift up light i mean that its on a lot, and i havent driven it i 1 or 2, just drive. so since i cant shift up and it keeps telling me to, it would further indicate i have a vac problem? also, i forgot to mention, i just got the car but im pretty sure the fuel cinsumption is horrible! i havent been able to check stuff out since its been raining like crazy, then letcha know
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Old 16th April 2011
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Auto's don't have shift lights or they would be manuals!!!!!
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  #11  
Old 16th April 2011
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Quote:
Originally Posted by pepper View Post
by whats with the shift up light i mean that its on a lot, and i havent driven it i 1 or 2, just drive. so since i cant shift up and it keeps telling me to, it would further indicate i have a vac problem? also, i forgot to mention, i just got the car but im pretty sure the fuel cinsumption is horrible! i havent been able to check stuff out since its been raining like crazy, then letcha know
weird! Remove the bulb!
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  #12  
Old 16th April 2011
pepper pepper is offline
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hmmm, so the shift up light isnt a diagnostic clue pertaining to the vacuum, rpm thing? Im wondering if my problem could be related to the AIC or AMM? I feel like a hose leak wouldnt trigger a shift up light, but then again I would think thr check engine light would come on if it were something big. The shift light doesnt really bother me, just confusing, or id take the bulb out...
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  #13  
Old 17th April 2011
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Your upshift light should be a combination of RPM, throttle position, and one or two other factors, but I believe the ECU controls the light. The 5th gear switch is so combinations that would normally light up the light are shorted to ground, since you can't up shift.
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  #14  
Old 17th April 2011
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If it's not a vacuum leak or something else obvious, it could be the ECU. Some 1989 ECUs have a reputation for unreliability. Might be why you're getting a shift light in an automatic...which is weird.
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