Car jerking on acceleration

[tookien]

So the saab 9-3 Turbo 2.0T manual has a jerking on acceleration.

Idle is fine.
Increasing the RPMs/throttle at idle is fine.

1st gear takeoff it's fine.

It's only when the car is cruising at a speed and then you want give it more gas abruptly (step down on the accelerator pedal) it will jerk randomly.

If you just ease the accelerate pedal and let it accelerate it's fine.

It's like a misfire on one or more of the cylinders but a misfire only while driving not on idle.

I changed one of the coil packs a month ago, it seemed to solve the problem.

Now it came back.

There is no CEL.

The spark plugs are relatively new. Installed them last year.

Things I did:

- tried different coil packs
- checked cracks in hoses and vacuum leaks
- checked air filter
- cleaned up sensors like MAF
- cleaned up the throttle body (gunk)
- checked various solenoids for functionality (turbo boost etc...)

Possible issues:

- still one or more of the coil packs is bad. these are all OEM but used ones
- spark plugs need to be replaced
- exhaust leak somewhere?? (not likely)


Any ideas? Thanks

 

[Lubener]

Sounds like a misfire to me. Many times a misfire will only occur when the engine's load is increased.

 

[JimPghPA]

There's a chance that it could be a fuel filter problem. Some of the more sophisticated diagnostic equipment could probably tell you whether the engine is trying to trim to make it richer because it's detecting that it's running too lean. If that were the case then it would also point to a fuel filter problem, or possibly a fuel pump problem. How many miles are on it? That's a good indication of whether or not it might need a fuel filter replacement.

 

[JimPghPA]

You could try a bottle of Redline SL-1 in the fuel tank and see if it clears up after you ran that tank out. If it clears up then it could be that the fuel filter was clogged to the point where it was starting to cause a problem and a good fuel system cleaner would temporarily clear up enough area in the media of the fuel filter to allow it to have proper amount of fuel for a while. But eventually it will come back because the filter would be on the edge of causing a problem with the amount that would still remain in it. But it would be one way to diagnose whether the fuel filter might be the problem. And it will clean up the rest of the fuel system for you.

 

[ctechbob]

Sounds like boost is blowing out the spark. Try to decrease the gap on the plugs a bit if you want to narrow it down. If the coils are getting weak it could get you by until you replace them.

 

[tookien]

thanks guys,
that all sounds reasonable options.

will get back what solves it

 

[Urshurak776]

I had a similar issue and it was the crank shaft position sensor.

 

[atikovi]

Sounds like a throttle position sensor problem, like it has a dead spot. Will it run with the TPS disconnected? If so, drive it and see if the problem reoccurs. I just picked up an 05 Saab turbo so interested in what you find.

 

[Marcozi]

Is the car obd1 or obd2? Scan the engine computer if it's obd2. The Service Engine Soon (SES) light is on only when an emissions related code is present,

 

[Barkleymut]

pull the plug where you had the bad coil before, see if it looks normal.

 

[twX]

Could be a rich or lean misfire. I'm leaning toward a fuel pressure issue or a bad MAF sensor or crankshaft position sensor. Check for loose or corroded sensor connectors.

 

[tookien]

Sounds like a throttle position sensor problem, like it has a dead spot. Will it run with the TPS disconnected? If so, drive it and see if the problem reoccurs. I just picked up an 05 Saab turbo so interested in what you find.

I really highly doubt it's the throttle position sensor.

 

[mrbreezeet1]

Sounds like a misfire to me. Many times a misfire will only occur when the engine's load is increased.

Sure! Now what about plug wires, or is this a "COP" system?
If it has plug wires, get you a plant sprayer bottle and open the hood of course, do it at night in the mostly dark of night. Mist a bunch of water on all the spark plug wires, and also the coils where the wires attach to the coil(s} Then snap the throttle and see if you can see any arcing anywhere.

 

[LongTime_Lurker]

Did you use SAAB ignition coils with the black tops (improved version) or yellow tops (stock)?

 

[meep]

If it’s more prone to do this at lower rpm/higher gear, then it’s a high-voltage side of the coil problem. It takes more voltage to push across the spark gap when the fuel/air mix is dense. if this is coil on plug, it’s the beginning of a coil failure, most likely.

upon reinstallation, make sure your plugs are gapped properly.

 

[brages]

I'm guessing something to do with the Saab Trionic knock dectection system because I don't know anything about it other than that it exists.

 

[ElectroMechanoMan]

My personal experience with a miss under load has mainly been with old tractors and 90% of the time it was bad spark plugs.Even pre fuel injection cars and trucks would do this. Personally, I’d try that first.

 

[sloinker]

Check your motor mounts.

 

[CarDoc66]

I would monitor misfire data on a scan tool while the condition happens. If you have a scanner that can read misfire data have an assistant drive while you monitor each cylinder. Or you could just throw a set of plugs at it and see what happens.

 

[tookien]

Problem solved.
Turns out, it was the plugs after all.
I didn't suspect them as they were newer plugs.

It probably had to do with the weak coils, making the ECU compensate with more fuel, and the gap on the spark plug was at the max range.

Swapping out coils made no difference.

I bought a set of new plugs and set the gap in the lower gap range, taking @ctechbob s advice here
The coils should be better than before as well.

Runs great now