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Discussion Starter #1
OK, bought my 2006 Saab 9-3 Aero three months ago, I'm now totally frustrated, I've had a Volvo T5 before so I know what 250 Bhp should feel like, however the Aero has a definate problem, my average mpg is 14.5 and it runs and feels like it's putting out around 200 Bhp with a slight surging when on steady throttle and decelerating.

Here is what I've done so far, new stock plugs with stock gap, cleaned Maf Sensor, taken it into local Saab dealer who put a Tech 2 on it and found no faults with any of the sensors or any codes logged.

I live in Florida, so the average temperature is between 90-100 degrees at the moment, we had a couple of wet days last week, when the temp came down to about 79 degrees and the car started running a little better.

I'm putting my money on the problem being a sensor, however which one I don't know, I'm open to advice as all of them are expensive to buy.

I'm thinking the problem could be the MAF sensor throwing out wrong information, if anybody has any ideas or has suffered similar problems I'd be interested to hear about possible solutions.
 

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OK, bought my 2006 Saab 9-3 Aero three months ago, I'm now totally frustrated, I've had a Volvo T5 before so I know what 250 Bhp should feel like, however the Aero has a definate problem, my average mpg is 14.5 and it runs and feels like it's putting out around 200 Bhp with a slight surging when on steady throttle and decelerating.

Here is what I've done so far, new stock plugs with stock gap, cleaned Maf Sensor, taken it into local Saab dealer who put a Tech 2 on it and found no faults with any of the sensors or any codes logged.

I live in Florida, so the average temperature is between 90-100 degrees at the moment, we had a couple of wet days last week, when the temp came down to about 79 degrees and the car started running a little better.

I'm putting my money on the problem being a sensor, however which one I don't know, I'm open to advice as all of them are expensive to buy.

I'm thinking the problem could be the MAF sensor throwing out wrong information, if anybody has any ideas or has suffered similar problems I'd be interested to hear about possible solutions.
You installed new plugs, but did you change the coil-packs? Made sure there are no vacuum leaks? is your exhaust especially sooty and were your old plugs coked up? (this would indicate bad MAF or o2 sensor)
just a stab in the dark.
 

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Discussion Starter #3
New Plugs

I didn't want to make my first post too long by going into great detail, I've inspected for vacuum leaks and none were found, the original plugs I took out were running greyish brown (correct colour). I bought these coil packs http://www.ebay.com/itm/290617080953?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649 from Ebay, the first one I put in had a securing bolt made of butter and broke off in my head, so I didn't put any more of these in and put the orginals back instead. I forgot to mention that the throttle body was cleaned as well. It's difficult to see if the exhaust is running black, I would say that it wasn't especially sooty. I can't say that I would discount coil packs, although I would have thought they would cause a misfire under hard acceleration rather than the symptoms that I have.
 

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Sounds like coil packs to me you can always test and inspect them by pulling them one by one while the cars running. I have the four cylinder so I'm sure its a bit easier for me though.
 

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Discussion Starter #5
Pinpointed the problem (almost)

OK, found a lot more information out, the problem is being caused by the AC being turned on. As soon as you turn the AC off the car drives perfectly and mpg goes up to around 22 mpg. I checked the battery and it looked like the dealer I bought it from put a Toyota battery with 525 ccw rating, the car should have a 700 ccw rating on it.

Anybody like to guess if this is the culprit, could a battery cause this problem, or is it more likely to be Alternator, AC Compressor or a short somewhere.
 

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OK, found a lot more information out, the problem is being caused by the AC being turned on. As soon as you turn the AC off the car drives perfectly and mpg goes up to around 22 mpg. I checked the battery and it looked like the dealer I bought it from put a Toyota battery with 525 ccw rating, the car should have a 700 ccw rating on it.

Anybody like to guess if this is the culprit, could a battery cause this problem, or is it more likely to be Alternator, AC Compressor or a short somewhere.
As I've stated in some other posts, I get horrible MPG, right around 12. I've done nearly all of the things you've done with no improvement. I have HP tuners so I can log data, nothing out of the ordinary shows up.

Living in warm weather I have the A/C on all the time, that combined with city driving, summer tires might be what it comes down to. Changing the battery is not going to help. At one point I bought a charging monitor that you plug into the cig outlet, with the A/C on the charging voltage drops from 13.7 to 12.7 might go even lower depending on how fast the blower is moving.
 

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thats strange, I have an 06 aero too and by no means is it fast, quick yes, fast no. I have a 2.0T combi too and the aero is faster for sure, not by a lot but noticeable. I live in FL too, if you are near St Pete/Bradenton, Sarasota, PM me and I will let you drive mine for comparision. around town I have been averaging around 17.5-18.5, today on the interstate I babied it (ac is always on this time of year) and at 70mph i averaged almost 28mph (I reset the trip cpu in route). it is a 6 speed so I do think that helps slightly with gas mileage. I was trying my best to stay out of it too and keep the boost down. No idea what could be going on but clearly something is up.
 

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Discussion Starter #8
Noooooooooooooo!

Please tell me I havn't got a car that runs like crap when it gets hot, (I live in Tampa by the way). I went to the Saab dealer earlier today and the service manager told me that he had driven these cars and was still averaging 21-22 even with the AC on, he mentioned that it could be the AC system that has been over presurised, that could be causing the engine to labour pushing the ac compressor.

I cannot believe that the AC system reduces mpg by a third as well as reducing power substantially, there has to be an answer to this.
 

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I find that hard to believe. If the pressure was high in the AC system the pressure switch should cut the compressor off? I guess something else could be causing a drag on the engine, like a bad bearing or something in the compressor since it runs better w/o the ac on? I wish I could offer more help man. Good luck.
 

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Discussion Starter #10
Compressor?

I did think that it could be a bad bearing or the clutch faulty on the compressor especially as the tick over rises by 300 revs when the AC is turned on.
 
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