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Discussion Starter · #1 ·
Hi everyone,

So I just got my 2000 saab 9-3 about a month ago. I had been running mid grade 91 octane in the car since I got because the car had been sitting for a year and I wanted to clean out any water in the system.

Yesterday, I went to fill up my tank that was almost on empty. I decided because of cost to fill it up with regular instead of midgrade (Exxon station). Wow, let me tell you that car didn't like the change at all. I figured the cpu would make the changes without a problem.

When I park the car and let it idle, the idle is high about 1500 rpm I believe. Its never been that high and the engine seems to be accelerated. When the car is in drive its down to 1000 rpms (the norm). I was somewhat surprised to see that the octane had such a quick effect on the engine idle.

Anyone else running regular instead of midgrade? Also I don't have the manual but what does SAAB recommend on these?
 

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Some one will add additional information but Saab's are particular to gas types. I use Shell or Sunoco gas where I can find it. 89 octane is fine however if your car is reacting to it it might point to a problem with your spark plugs or the DIC. Were the plugs changed prior to or when you purchased the car?

maybe try a octane booster :roll: to see if it helps. I rolled my eyes as I don't really believe they do anything to a full tank of gas unless you used 5 or 6 bottles which then defeats the cost savings of using a lower rated pump gas... ....

In any case good luck and hope it solves your problem....Stick to Shell gas though if you can. ;ol;

ps... .you didn't state if you dropped the tank or used some kind of fuel stabilizer to conteract the effects of old gas sitting in the tank for a year...could be that... the old stuff is running throught the system. As dropping the tank is a major PITA, check the plugs, test the DIC, change the fuel filter, inspect the injectors spray pattern if your able, run with better gas. GL!
 

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I run the 10% ethanol BS we have here in Iowa (89 octane) and my saab seems fine with it.
 

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Hi everyone,

So I just got my 2000 saab 9-3 about a month ago. I had been running mid grade 91 octane in the car since I got because the car had been sitting for a year and I wanted to clean out any water in the system.

Yesterday, I went to fill up my tank that was almost on empty. I decided because of cost to fill it up with regular instead of midgrade (Exxon station). Wow, let me tell you that car didn't like the change at all. I figured the cpu would make the changes without a problem.

When I park the car and let it idle, the idle is high about 1500 rpm I believe. Its never been that high and the engine seems to be accelerated. When the car is in drive its down to 1000 rpms (the norm). I was somewhat surprised to see that the octane had such a quick effect on the engine idle.

Anyone else running regular instead of midgrade? Also I don't have the manual but what does SAAB recommend on these?
Well, I have never heard of octane making such a drastic idling change. Were it mine, I would clean the AIC (2000 still used the AIC) first and check ALL my vac lines.
 

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Discussion Starter · #7 ·
Hi everyone,

Saaboheme you got it right.

Well it didn't make much sense that the idle surged so much after the octane change. Today when I got to work I popped up the hood and saw that one of the vac lines in the rear had popped loose! I connected the line back up and the idle went back to normal.
 

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depends on the year 9-3. late in year 2000 the ems was changed from tronic5 to tronic7. with this change came an electronic throttle body that controls idle
Absolutely. The OP did not specify, and with his idle variations, it sounded like it could be a bad AIC, if he had one, or a disconnected vac line.
 

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Everytime you fill up with more than 10L on a T7 car the ECU resets it's fuel trim to zero and starts adapting again. Also if you had a 5-10% E85 previously in the 91 fuel it would need a bit of time to adjust. It should only be briefly though so if the idle has not settled down you have some other fault.
 

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my rule of thumb with a turbo charged vehicle is always to use high octane gas.
 

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I'd never out 89 in my car - don't think we even have it in this country. Nothing less than 97 in mine. I don't think the ecu can retard the timing enough for such low quality fuel.
 

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We don't use the RON octane rating number here like you folks in Europe. Our pumps display the average of the RON and the MON (research octane rating and motor octane rating). Accordingly, our pump numbers are lower than yours, by around 4 points. So our 89 is pretty much equivalent to your 93 and our 93 would be pretty much equal to your 97. And Trionic, when functioning properly (meaning all sensors and ancillary equipment properly operating as well) should be able to adapt to regular unleaded, which is 87 here and 91 or 92 there. Performance will suffer however, as the ECU will need to retard timing and add a little extra fuel to the mix to prevent knock. Under extreme operating conditions, it will dial down boost when all else fails.

In the November 2001 issue of Car & Driver they tested several cars. The full article is here. Below is the relevant excerpt of the performance results of higher and lower octane in these several cars, including a Saab.

Let's meet the test cars and ponder the results. At the lower-tech end of the scale was a regular-gas-burning 5.9-liter Dodge Ram V-8. This all-iron pushrod engine has a mechanical distributor and no knock sensors, so the computer has no idea what grade of fuel it's burning. A Honda Accord V-6 with VTEC variable valve timing represented the mainstream-family-sedan class, and a 4.6-liter V-8 Mustang stood in as an up-to-date big-torquer. Both of those were designed to run on regular unleaded. Our premium-grade cars included the hard-charging 333-hp, 3.2-liter BMW M3 straight-six boasting individual throttle by wire for each cylinder and enough computing power to run Apollos 11 through 13. A Saab 9-5 gave us a highly pressurized 2.3-liter turbo. For the sake of repeatable track testing, all but the M3 were equipped with automatic transmissions.
We ran all vehicles on both grades of fuel, at a drag strip near our offices and on a Mustang eddy-current dynamometer that was offered to us by the engine-tuning pros at Automotive Performance Engineering in nearby Clinton Township, Michigan. On arrival, all fuel tanks were drained and filled with 87-octane Mobil regular fuel and driven for two days before track and dyno testing. The tanks were drained again and filled with 91-octane Mobil premium and again driven for two days to allow time for the engine controllers to acclimate to the fuel type and tested again. All dyno and track results were weather-corrected.
Our low-tech Ram managed to eke out a few extra dyno ponies on premium fuel, but at the track its performance was virtually identical. The Mustang's knock sensors and EEC-V computer found 2 hp more on the dyno and shaved a more impressive 0.3 second off its quarter-mile time at the track. The Accord took a tiny step backward in power (minus 2.6 percent) and performance (minus 1.5 percent) on premium fuel, a phenomenon for which none of the experts we consulted could offer an explanation except to posit that the results may fall within normal test-to-test variability. This, of course, may also be the case for the gains of similar magnitude realized by the Ram and Mustang.
The results were more dramatic with the test cars that require premium fuel. The turbocharged Saab's sophisticated Trionic engine-control system dialed the power back 9.8 percent on regular gas, and performance dropped 10.1 percent at the track. Burning regular in our BMW M3 diminished track performance by 6.6 percent, but neither the BMW nor the Saab suffered any drivability problems while burning regular unleaded fuel. Unfortunately, the M3's sophisticated electronics made it impossible to test the car on the dyno (see caption at top).
Our tests confirm that for most cars there is no compelling reason to buy more expensive fuel than the factory recommends, as any performance gain realized will surely be far less than the percentage hike in price. Cheapskates burning regular in cars designed to run on premium fuel can expect to trim performance by about the same percent they save at the pump. If the car is sufficiently new and sophisticated, it may not suffer any ill effects, but all such skinflints should be ready to switch back to premium at the first sign of knock or other drivability woes. And finally, if a car calibrated for regular fuel begins to knock on anything less than premium or midgrade, owners should invest in a tuneup, emissions-control-system repair, or detergent additives to solve, rather than bandage, the root problem. Class dismissed.
 
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