"Rough" idle sign of a head gasket issue?


#1

Car: Saab 9-3 / 2000 model

Miles: approx. 110K



When you first start the car in the morning it has a ‘rough’ idle but is fine after a minute and is also fine the rest of the day.



Is this a sign of a problem with a head gasket?



Thank you!


#2

Probably not. Any sign of oil and coolant mixing, either in the oil pan or the radiator? Are you using a lot of either fluid? Billows of white smoke from the tailpipe after the engine and exhaust system have warmed up? These are some of the classic symptoms of a blown headgasket.


#3

Thanks for the quick reply NYBo!

Not sure on the first question. We did get the “Fill Coolant Fluid” warning message on the display recently, which prompted me to take it to the shop. No white smoke from the tailpipe that I’m aware of.

Thanks again!


#4

There are ways to detect a bad headgasket, some easy. If the radiator bubbles with the cap removed and the engine running, that’s the combustion gasses being blown into the water jacket and migrating out. There’s a test strip you can buy to check the coolant for the presence of hydrocarbons in the coolant, again an easy check. And, there’s always a pressure leakdown test, where the cylinders are pressurized with air and their ability to hold pressre monitored. That last one is easy in a 4-banger but can be a pain on a V6 if the rear bank is hard to access. I confess to not knowing if the 9-3 is a four or six.

A headgasket breech will cause a rough idle, but it usually becomes more apparent under load, when the pressures in the cylinder are the highest. You will usually also detect loss of coolant, as the vacuum in the cylinder spikes on deceleration and the pressurized coolant (most that I know operate at about 15-16 psi) gets drawn into the cylinder and vaporized.

If the breech is also into the oil passage, it’ll also allow coolant and combustion gasses to mix with oil and the coolant will get gumped up. You’ll see this a a glob and/or discolored coolant under the radiator cap.

(copied from AC post)


#5

It’s not likely a head gasket problem. You may have a failing fuel pump.
The fuel pump has a check valve in it that allows the system to maintain fuel pressure when the engine is at rest. This assures the engine will start instantly.

When the check valve assembly wears (think of a leaking water valve in a toilet), or there are some contaminants wedged in there the ball will not seal on the seat completely.
When you turn the engine off fuel pressure will bleed off and air will be present in the lines. Sometimes it takes all night for this to happen.

The rough running you have may be the air being purged out of the fuel lines. To test this in the morning turn the key to the RUN position for a few seconds without starting the engine. Turn the key off. Repeat this process 7 or 8 times and start the engine. If it runs fine you’ll know the check valve is the problem and this means a pump replacement along with the fuel filter. Hope that helps.

There’s a few other things it could possibly be but that’s what I’d look at first.


#6

Is this how one might be able to pick up an otherwise good Saab for $20? ;0)


#7

Well, it worked for me. The neighbor actually offered the SAAB I currently have to me for one dollar. Thinking I heard him wrong (have a hearing loss problem) I repeated it and he verified it.
I just simply could not bring myself to give somebody a single dollar for a car so I threw in the other 19 dollars as a tip to make myself feel better. :slight_smile:


#8

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