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SAAB Project Update: Running Rough When Warm


We may have celebrated prematurely. After taking the SAAB out on a long drive the other day, the surging idle and stalling issues reared their ugly heads again. So, I went ahead and replaced all the vacuum hoses and one of the cracked intake manifold fittings. It fixed the vacuum leaks, but it wasn’t the definitive solution. That’s okay though because it is better to replace that which is cheapest first rather than throwing money at parts that might not even be bad. New hoses didn’t solve the problem so we will have to continue our detective work.

The engine runs great when cold. It idles right where it should and pulls hard when accelerating. It is obvious that the new hoses made a big difference and you can almost convince yourself that the problems have been fixed. That is until things warm up and then all hell breaks loose.

The rev counter starts bouncing up and down and then the engine stalls when rpms get too low. A dab of throttle can usually keep things going, but by the time everything is up to operating temperatures, the car is bucking and barely drivable. The air/fuel system is obviously having a hard time figuring out the ideal mixture. Watch both of the videos we posted on YouTube and you will see what we mean. Something is still not right. It is fun to diagnose this sort of stuff together and we all learn more, so any guesses?

Latest Project Updates


  1. Todd N

    Clean and adjust the Air Idle Control Valve (AIC). Search the saabnet.com forums and I’m sure it’s been discussed many, many times.

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    • Jesse Mortensen Jesse Staff

      Already cleaned it Todd, but it wasn’t dirty at all actually. Perhaps it is going bad?

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    • Marc Lawrence

      Ignition control module – replace – SOB unit would be better than aftermarket

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    • Off2hcky

      IACV was my first guess. We used to have an RX300 that did the same thing. Had to clean that bugger once a year. Not sure how Saabs are but the Lexus one was round inside and you can twist it like a thumb screw. I would clearly feel the resistance when it was dirty. A good dose of deep creep would free it up nicely.

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  2. Jax

    Replace the SAAB…problem solved

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  3. Jax

    oops I meant replace SAAB with Miata …problem solved

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    • Jesse Mortensen Jesse Staff

      I’m starting to think that might not be such a bad idea. Gotta get the SAAB running right though before I can sell it on.

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      • BobinBexley Bob in Bexley Member

        Jesse, you get it running right you might not want to sell it. SAAB ownership is an addiction, if it’s turbo then you’re in deep- nothing like the rush of driving a well tuned 900T !

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  4. Rich

    I had this problem with my F150 recently. To make a long story short it was my fault. When I did a tune up on it the number one plug wire wasn’t snapped in properly.

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  5. Rev. Rory

    Ah, yes, welcome to the world of elderly SAAB health care. I can just about guarantee that when you are done finding all the little things to fix you will need tires. Those things consume money in $500 chunks, and seem to keep JUST behind the resale price curve… ;-)

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  6. Stu

    Make sure the oil fill/dipstick is seated correctly. If it is only caught on one side it will allow a crankcase vent condition that will mess with the mixture.

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  7. BobinBexley Bob in Bexley Member

    Unplug the MAF with engine running & warm.

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  8. Dolphin Member

    Some simple things to try:
    1) coolant temperature sensor
    2) air flow meter

    Find or make a friend who has a similar car and ask of you could swap a part in briefly as a test. The air flow meter will be easy to swap in & out. The coolant temperatore sensor gets you into draining coolant, so better to try to get one cheap from a wrecking yard, online, or from a cheap supplier.

    Out of ideas now….time for a cold beer. Good luck, Jesse.

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  9. Mike

    Does this car have fuel injectors? Sounds like fuel injectors to me. If they are bad, they can run fine cold, and stutter when warm.

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  10. Dave @ OldSchool

    I forgot what year the Swede is ……….what does it have for a coil ?????????? resistor ??

    coils act that way when they get too hot … messes up the tachometer too……..

    If the key was left on for a while ,with the motor not running, it sometimes causes shorts in a coil that later show up this way

    Electric fuel pumps can do the same ( get heat damage) if the tank is often allowed to run dry..then they don’t produce consistent flow

    If you don’t think it’s electrical or fuel, stick a vacuum guage on it ..but ususally vacuum leak won’t care if it’s hot or not…..

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  11. Kevin

    Couple of suggestions:

    Clean the throttle body-scrub it with a tooth brush-swap out the AMM (air mass meter) with a known good one. You may still have a bad AIC even though you’ve cleaned it-try swapping that with a known good one. My guess is its a bad AMM-I went thru several on my Classic 900’s.

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  12. Mohamed Ragab

    Two suggestions :
    1. May be one or more of the plug wire needs to be changed.
    2. You might need to have a look at the fuel censor
    That’s my humble diagnosis to the symptoms

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  13. Jim-Bob

    The first thing that comes to mind for me is what is called a thermal vacuum switch. I am not certain your car even has one, but it is a vacuum switching valve that opens or closes only after the engine has heated up. They are normally screwed into the block or manifold somewhere that lets them connect to the coolant passages. Otherwise, I would look at things that normally do not get read while the engine is in open loop operation but are read when the engine goes into closed loop. The most obvious of these is the oxygen sensor. The O2 sensor is essentially a battery that creates an electrical potential by comparing the amount of oxygen in the exhaust to the amount in the outside air (this is why they have those small louvers on the side). If it has failed, then you will see no oscillation in the voltage output from the output wire (check from the block as a ground to the sensor wire). It may be that it is reading pig rich all the time and so the ECU has trimmed the fuel down to nothing. I would also try disconnecting the sensor and see if it runs better in constant open loop, thus mimicking the way the computer works during warm up.

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  14. John Schreiber

    Clean the throttle body. Make sure the throttle switch clicks at the closed throttle position. Plug the line to the brake booster to eliminate it as a vacuum leak. Spray carburetor cleaner on the at the injectors/ throttle body, intake fittings and near the turbo bypass valve, turbo intake boot, and outlet boots. Engine will pickup when you find the air leak.

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  15. Chip Lamb

    Since you’re probably tired of the majority of replies with cliches and the like:

    Step 1 – purchase a Robert Bentley SAAB 900 16V service manual
    Step 2 – carry out the overly complicated base idle setting procedure that involves the throttle position sensor mentioned therein, a lot of the time this is all that it is, someone jacked with the idle screw (10mm bolt with locknut on throttle body) when this was not how to do it!
    Step 3 – just for the hell of it, ohm out the air idle control valve mentioned earlier, make sure that it has 20 ohms +/- 2 between pins 1-2 and 2-3 and 40 ohms +/- 4 between pins 1-3.
    Step 4 – With car off, check resistance between pins 3 and 6 on the air mass meter. You should see in the range of 380 ohms. If it’s close, dial it in by removing the blanking plug on the side of the AMM body to get it close and see if you have a change particularly in cold start hunting.
    Step 5 – check wiring harness in engine bay for degradation
    Step 6 – test O2 sensor for voltage swings

    If none of the above sorts this out, I suspect you are suffering from Air Mass Meter failure as mentioned above by another commenter.

    Saab dealer tech in this era

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  16. John J

    You need to just post your issues in detail at http://www.saabnet.com/tsn/bb/900/
    I will bet within a few days you will have it fixed. Stop searching and start asking!

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  17. pursang

    Test or replace your O2 sensor. Had a 92 900S once and put 245,000 miles on it with not too many problems. Sold it to another guy who ran it three more years before I lost track of it. Recall a floating idle when hot was an O2 sensor issue.

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  18. mark

    If this has CIS, did you check, and or replace the air intake boot? Also WUR.

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  19. John J

    Follow Chip Lamb’s advice. He is a recognized expert on these cars.

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  20. JW

    Are you running quality gas and the 92 octane?
    Anytime my cars are running rough the first thing asked by my mechanic is what gas are you using? I’m sure the debate will begin but I’ve found w/ European cars, you need to use good gas w/ cleaners and the minimum octane the manual requires.

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  21. maserati

    Jesse,did you checked the Airhose from the Trottel Body to the Air intake? Take it out and check the Bottom side of it. Had the same Problem with the RPM and that what it was,a hole in there.

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  22. John

    On my Dad’s Saab, we looked for weeks and finally discovered a bad distributor cap. It was much like yours, it didn’t show up till it was hot. We checked the wires and the inside of the cap several times and they were always fine, but we never thought to check to see if there was actual conductivity through the cap. I’m no expert — just thought I’d offer an idea.

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  23. Jesse Mortensen Jesse Staff

    Thanks for all the great recommendations guys! I am going to start the troubleshooting process tomorrow and will let you know how it goes. Now, where did I put the multimeter?

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  24. BobinBexley Bob in Bexley Member

    Jesse, any up-dates ? I’m dyin’ here ! If a person doesn’t love a SAAB then they don’t understand the other side of the Swedish brain !

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  25. colin

    Stupid thought but if its a carb version might be worth checking the thermostat as the carbs are water cooled, that would cause overheating of the carb and vapour lock problems.

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  26. Franke

    An exorcism is in order, see a priest at once.

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  27. MikeW

    try replacing the stator in the the distributor.

    Like 0

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