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Discussion Starter · #1 ·
My 1989 Saab 900 turbo 16v seems to buck when i lightly press the gas or just randomly when im lightly on the gas to maintain speed. Whenever these bucks happen the rpm needle goes from 0 to about 4k back and forth. I have replaced the alternator, fuel filter, o2 sensor, checked vacuum lines and cleaned the AMM. Spark plugs where changed about 3 months ago. Sometimes when i lightly press the gas the rpms go to 0 and the CEL comes on for a few seconds until the rpms go back to normal. I also have a small crack in my muffler but i dont think that would cause all of this.
 

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sounds bizarre but I'd suggest you check all your grounds, on your battery, on the radiator cross member, clean and tighten cover with vaseline to prevent corrosion etc. the engine can't rapidly go to 4k rpm in gear like that, so to me it sounds like an electrical short bad connection etc.

sounds like you've done all the common wear and tear items, I'd be looking towards that or even a faulty ignition amplifier. if you have a bentley perhaps do the testing procedure for it.
 

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My 1989 Saab 900 turbo 16v seems to buck when i lightly press the gas or just randomly when im lightly on the gas to maintain speed. Whenever these bucks happen the rpm needle goes from 0 to about 4k back and forth. I have replaced the alternator, fuel filter, o2 sensor, checked vacuum lines and cleaned the AMM. Spark plugs where changed about 3 months ago. Sometimes when i lightly press the gas the rpms go to 0 and the CEL comes on for a few seconds until the rpms go back to normal. I also have a small crack in my muffler but i dont think that would cause all of this.
Another Coloradoan rescues a Saab...welcome to the board! :)

This might sound crazy, but check and see if there is a [edit[ light guage [/edit] ground wire that runs from the inner fender under the hood on the drivers side to the oil fill pipe or somewhere in that vicinity. Also check and see if the vacuum hose to the pcv check valve has come off the fitting in the manifold.
 

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1989 are known to have cranky ECU

I have an 89 and had random idle and the check light would come on all the time. Not exact symptoms, but if you've never replaced the ECU, your overdue. I'd swap in another one just to check if you can find one handy.
 

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My 1989 Saab 900 turbo 16v seems to buck when i lightly press the gas or just randomly when im lightly on the gas to maintain speed. Whenever these bucks happen the rpm needle goes from 0 to about 4k back and forth. I have replaced the alternator, fuel filter, o2 sensor, checked vacuum lines and cleaned the AMM. Spark plugs where changed about 3 months ago. Sometimes when i lightly press the gas the rpms go to 0 and the CEL comes on for a few seconds until the rpms go back to normal. I also have a small crack in my muffler but i dont think that would cause all of this.
Welcome to my world. I have replace the distributor, AIC, NTC, vacuums lines, new cap and rotor, new wires, cleaned the throttle and the AMM. I even cleaned all electric connections I could find.
My issue tends to be when the car gets warm or the rpm needle goes crazy. I just read on an article on SAABNET and they were having the same issue and had a new distrubtor cap and replaced it with the old one and it solved the issue. I plan to try this tomorrow and see if it works. If not it off to the shop.

Keep us posted.
 

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Discussion Starter · #6 ·
the car seems to run fine until it reaches operating temperature but i was planning on replacing the cap and rotor pretty soon so we'll see if that helps anything. replacing the o2 sensor helped a lot and the bucks aren't as hard or as often so I'm also thinking the AMM might be bad since a faulty AMM seems to have a lot of the same symptoms of a faulty o2 sensor from what ive been reading.
 

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Welcome to my world. I have replace the distributor, AIC, NTC, vacuums lines, new cap and rotor, new wires, cleaned the throttle and the AMM. I even cleaned all electric connections I could find.
My issue tends to be when the car gets warm or the rpm needle goes crazy. I just read on an article on SAABNET and they were having the same issue and had a new distrubtor cap and replaced it with the old one and it solved the issue. I plan to try this tomorrow and see if it works. If not it off to the shop.

Keep us posted.
test your ignition coil kc
 

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S900t8v I took your advice and changed out the ignition coil. However, it did not fix the problem. I did make an adjustment to the bolt (about 1/4 turn) where the throttle links to the cable. and so far not erratic RPMs and it drives great. There is a little hunting idle only when in park. I'm sure I still need to do some adjusting of the nut. I thought I would pass this on and see if it helps anyone.
 

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S900t8v I took your advice and changed out the ignition coil. However, it did not fix the problem. I did make an adjustment to the bolt (about 1/4 turn) where the throttle links to the cable. and so far not erratic RPMs and it drives great. There is a little hunting idle only when in park. I'm sure I still need to do some adjusting of the nut. I thought I would pass this on and see if it helps anyone.
I said test not change

You cannot adjust an idle problem by adjusting the throttle stop.

1/4 turn clockwise or anticlockwise?
 
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