Inconsistent/rough idle

[Saabster754]

I recently puchased a 2007 9-5 2.3t with 40k miles. It seems to run fine and no warning lights come on but the engines idle seems rough and inconsistent. This usually happens when I'm sitting at a stop light or when the car is in park. The idle will slowly drop lower and lower making the car vibrate a little. I'm not sure if this is related but it also feels as though i need to press harder on the brake to keep it from moving at a stop light. I have had a dealer look at it and they said nothing was wrong. I had another dealer tell me it is because of the poor quality of fuel where I live even though I only use 93 octane. I tried a fuel additive and it did smooth things out a little but I feel that a car of this quality/age/miles should feel pretty smooth without additives. Anyone have any thoughts?

[nordwulf]

The 2.3T engine in the 9-5 has never been the smoothest but the problem you're describing is unusual.

My previous 2006 9-5 had some idle problems and that was caused by loose vacuum house on the throttle body. A local car parts store suggested adding HEET to a tank off fuel in case there is a water in the tank.

There is a TSB in the WIS but it doesn't sound exactly like the same problem. What are the RPMs on your car? When was the last time the spark plugs were changed?

TECHNICAL SERVICE BULLETIN
Bulletin Nbr: 248-2565
Date:...........Juni 2005
Market: US/CA
Vibration at idling speed
Cars affected
Saab 9-5 M98- with engine alternative B205, B235 and B308

Background
In certain vehicles, the vehicle may vibrate when it is stationary.
Vehicles equipped with automatic transmission may have the idle speed set higher than the typical idle speed. While the vehicle is in this condition, the driver may experience abrupt shifts as the shift lever is moved from park to drive or reverse.

Symptom description
Vibration in the body while stationary. Abrupt shifts as the shift lever is moved from park to drive or reverse.
Parts required
Not affected

Procedure
1. Establish whether the car has idling speed vibration problems or shifts abruptly.
2. Adjust the engine's idling speed. Connect Tech2.
• • • • • • •
If the car exhibits vibration problems during cold starting for example, then the speed should be increased at a minimum (10 - 30 rpm). If the problem remains at all engine temperatures, then increase the speed by more than 30 rpm.
If the vehicle shifts too abruptly when engaging gear, lower the engine speed in steps of 20 rpm.
If the car is equipped with automatic transmission then the customer should be informed that the tendency to shift abruptly will increase if idling speed is increased.

[niskanem]

seems early for vacuum line cracking or issues with the fuel filter or plugs.... but I guess you never know. that's where i'd start.

[Saabster754]

The car has 44,000 miles on it. Still has original plugs. The manual suggests replacing at 40,000 and dealership says they get replaced at 60,000. When the car is in park the idle seems like it wants to be around 860 (as manual indicates) but it drops down just above 750 and the needle slowly goes up and down very slightly. When in drive but at a stop the needle still goes up and down very slightly but it is much closer to the suggested RPM's. I have noticed the abrupt shifts, as mentioned above, but its usually only when the engine is cold and the car has been sitting. If the engine is still warm from a recent drive the shifting from park to drive is usually very smooth.

[LEGage]

So you can rule out the fuel filter your model does not have one, or if it does it is in the tank where you can not get to it.

I would take things in steps to help figure out what the issue is. I would change the oil first and see if it ran smoother. Then I would put in new plugs see if that helped(I think this is your issue. New plugs helped my car big time). Then a new air filter. If it is still running rough then I guess it would be the vacuum lines or your DIC. I had to put a new DIC about 5000 miles ago. You would most likely get error codes for that though.

I just changed my plugs, oil & oil filter, and put in a new air filter. I had my garage do the rest of my 60,000 mile tune up. I use Castrol full synthetic European formula 0W-30. The type of oil does not matter just make sure it meets the specifications laid out in the manual.

One other thing that I do that I DO NOT recommend (because it is a personal preference) is I use zMax. The reason I say do not do this is because now I feel I need to do it every oil change. It does make my car run smooth though. My gas mileage on my last trip back from my folks for 700+ miles was 33 mpg. That was using cruise control and staying close to the speed limits seeing how I was in different states and was in no rush.

I will be changing my plugs every 15,000 miles now, now that I can do it myself. I got clear tubbing from home depot with a 3/8 inside diameter to help put the plugs in. I also used some anti-seize and dielectric grease that I got from Auto zone. They were in small little packets that I got from the guys behind the counter. I recommend a torque wrench if you do the plugs yourself for making sure your tighten them up to proper specifications.

[Saabster754]

I think that's some good advice. I will take it step by step. I just had the oil changed so next I'll do the plugs and then the lines if it still isn't smooth. Thanks for all the help! I'll let you know how things go.

[nadrealista]

The 2.3T engine in the 9-5 has never been the smoothest but the problem you're describing is unusual.

My previous 2006 9-5 had some idle problems and that was caused by loose vacuum house on the throttle body. A local car parts store suggested adding HEET to a tank off fuel in case there is a water in the tank.

There is a TSB in the WIS but it doesn't sound exactly like the same problem. What are the RPMs on your car? When was the last time the spark plugs were changed?

TECHNICAL SERVICE BULLETIN
Bulletin Nbr: 248-2565
Date:...........Juni 2005
Market: US/CA
Vibration at idling speed
Cars affected
Saab 9-5 M98- with engine alternative B205, B235 and B308

Background
In certain vehicles, the vehicle may vibrate when it is stationary.
Vehicles equipped with automatic transmission may have the idle speed set higher than the typical idle speed. While the vehicle is in this condition, the driver may experience abrupt shifts as the shift lever is moved from park to drive or reverse.

Symptom description
Vibration in the body while stationary. Abrupt shifts as the shift lever is moved from park to drive or reverse.
Parts required
Not affected

Procedure
1. Establish whether the car has idling speed vibration problems or shifts abruptly.
2. Adjust the engine's idling speed. Connect Tech2.
• • • • • • •
If the car exhibits vibration problems during cold starting for example, then the speed should be increased at a minimum (10 - 30 rpm). If the problem remains at all engine temperatures, then increase the speed by more than 30 rpm.
If the vehicle shifts too abruptly when engaging gear, lower the engine speed in steps of 20 rpm.
If the car is equipped with automatic transmission then the customer should be informed that the tendency to shift abruptly will increase if idling speed is increased.

Frank,

My 95 fully warmed up idles @ 750 rpms according to the tachometer(~820rpm according to the OBD II software I have), when I put the car in drive engine rpms go to just a hair under 1000rpms and stay there with my foot on the brake pedal.

Most automatic cars will remain at or slightly below the rpms they run at idle in neutral/park when you put them in drive. Why is mine not doing the same? I doubt this is normal? This also cant be good for fuel economy especially if you do lot of stop and go city driving, not to mention putting additional strain on the clutches in the auto tranny.

If I am reading your post right the only way to adjust idle speed on my car is via Tech2?