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  #1  
Old 21-07-10
Szmek Szmek is offline
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Exclamation Hesitation + Jerking during low range boost

Hi ALL!

I've looked all over forums, but I can't find the answer to my problem

I'm experiencing a jerking and boost hesitation (fluctuating on/off) - but only on low RPMs (between 1,500-3000) and at around half throttle. There are no problems when I drive the car really steady and gently (in traffic) and no problems on WOT - car goes like a rocket boosting 1.1bar and then setting to 0.9bar. Sometimes when I let the car jerk/choke a little longer I get a flashing CEL (that disappears after sometimes x5, sometimes x15 flashes) - but it doesn't always come on.

It's really hard to drive it normal, because any quick manoeuvres (like overtaking) are really rough and erratic - so you can either drive it really slow or race it - nothing in between.

What I've done so far based on what I know and found in forums is:
- Clean TB and MAF (routine)
- New Air Filter (routine)
- Reset the ECU
- Changed the spark plugs
- Tried a different DI cassette (could be misfires with the flashing CEL)
- Tried a different APC/Solenoid (why is it opening and closing boost erratically)
- Checked what I could of the vacuum lines

I've had no luck and nothing seems to have fixed the problem. I'm really stumped. I have no idea what it might be. I would really appreciate any advice or opinions
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  #2  
Old 21-07-10
Idlewild Idlewild is offline
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I have somewhat similar issues, but no CEL yet.
My new throttle body arrives on friday and I think it's gonna cure my problems since there was some faulty cables inside the old TB electronics.
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  #3  
Old 21-07-10
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envoy envoy is offline
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Default Hesitation + Jerking during low range boost

I have a similar problem in warm weather and when the engine gets warm, but not sure what it is yet.
Very similar problems I've found here: http://www.saabcentral.com/forums/sh...d.php?t=187830
Seems to be a throttle body problem. I've PMed netmatt, hope he can help, since the thread ends in going to get a new TB, but not if it solved the problem
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  #4  
Old 21-07-10
Szmek Szmek is offline
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Thanks for the reply.

I was hoping that it wasn't as serious as that.

What sort of problems are you experiencing?

How did you diagnose the TB?

I've done the DI and the Solenoid, because they're pretty simple to plug and check from borrowed ones - but the TB is going to have to be a more costly operation.
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  #5  
Old 21-07-10
Idlewild Idlewild is offline
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I hade to take the TB apart to get to the wiring. There was no mechanical issues with it except that it needed cleaning, but the electronics were all messed up.

The issues I had was jerking and hesitation at low speeds and low rpms. Also when engine braking and when the throttle was in certain positions, usually on light throttle I could reproduce the jerkiness.

When switching to WOT the car would run like a charm.
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  #6  
Old 21-07-10
Szmek Szmek is offline
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Would any problems with the TB not throw a CEL? Or even a report when the Tech2 is connected?

Because I had a Tech2 connected, and aside from a few negligible things, nothing appeared reflected a damaged TB.

[I would just like to know for sure - because so far I saved a lot by NOT buying a new DI cassette, or a Solenoid, and the next step was to start looking at the turbo]
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  #7  
Old 21-07-10
Idlewild Idlewild is offline
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It does not throw a CEL until it's pretty much completely broken and goes into limp home mode. I guess it has to do with the +- readings that have to stay within some prevalued tolerance limits. So it can already be broken enough for the car to run bad but it stays within the tolerance so the engine thinks it's fine.
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Old 21-07-10
gemlam gemlam is offline
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I had jerking at low RPM and light to moderate throttle on my 2004 2.3l(manual transmission) since I bought it 2 years ago. Recently, my oil trap hose failed (the one way valve cracked which resulted in a major vacuum leak), eEuroparts part no 5955927. When I replaced this hose ($45 at stealer), the jerking was gone. I think that the plastic valve was cracked all along, and had a slow leak until it finally failed completely.
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  #9  
Old 22-07-10
Szmek Szmek is offline
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Gemlan - Did you have problems with the jerking at full throttle? By Oil trap hose do you mean the PCV system? Because I had the whole system with hoses changed about 6 months ago - hard to believe that it would fail so quickly.

I'm gonna see if I can swap in a different TB today - maybe it will fix the problem. I read somewhere that 'loose'/broken wires in the TB can cause this hesitation and it doesnt occur at WOT due to the current hitting maximum (or something along those lines) - like in Idlewild's case.
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  #10  
Old 22-07-10
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I've been having similar problems on my car during hot and humid days.

http://www.saabcentral.com/forums/sh...d.php?t=185066
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  #11  
Old 22-07-10
Szmek Szmek is offline
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Hi mfong.

I read your thread - some symptoms seems similar, however I'm not really blaming it on the weather conditions. I had the problems when it was cooler and theyre still there. Do you have power on WOT? Because mine boosts and roars like normal under WOT.

I had the problem with 1st gear at the lights a few times, where it just stuck and then suddenly just shot off (under slight throttle). But mostly its getting stuck in normal driving 3rd or 4th gear, trying to accelerate from around 2,000rpm.

Something new I discovered was a small backfire pop from the exhaust after it hesitated for a few seconds. Together with the flashing CEL I would have suggested engine misfires due to faulty DI, but that was replaced with a working one, and everything was the same (still bad). If we blame it on the TB, perhaps its limiting the air intake, causing unburnt fuel to backfire later in the exhaust? And the CEL is the same, warning of damage to the catalytic converter (which I dont mind, because I dont have one)

I'll try a new TB at my mechanics tmrw morning, although he sounds sceptical.
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  #12  
Old 22-07-10
gemlam gemlam is offline
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No problem with WOT, only light to moderate acceleration. And yes, the oil trap hose I think is part of the PCV system...It is the black pipe that runs across the back of the valve cover (left to right) and is clamped right at the one way valve connection approx center of engine.
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  #13  
Old 22-07-10
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Quote:
Originally Posted by Szmek View Post
Hi mfong.

I read your thread - some symptoms seems similar, however I'm not really blaming it on the weather conditions. I had the problems when it was cooler and theyre still there. Do you have power on WOT? Because mine boosts and roars like normal under WOT.
When my car is driving very sluggish that day, depending on the day, I have no power under WOT. However, when my car is driving great with no hesitation and jerks, I do have power.

When my car is driving poorly and under WOT, the turbo-meter would jump up to the end of the yellow border, and drop back down to the border between white and yellow. Out of frustration sometimes, I would roll my eyes and stomp on my gas pedal, because the car isn't going anywhere fast.

Quote:
Originally Posted by Szmek View Post
I had the problem with 1st gear at the lights a few times, where it just stuck and then suddenly just shot off (under slight throttle). But mostly its getting stuck in normal driving 3rd or 4th gear, trying to accelerate from around 2,000rpm.
When I get out of 1st gear, I try and rev it up higher than normal to reduce the severity of the hesitation.


Quote:
Originally Posted by Szmek View Post
Something new I discovered was a small backfire pop from the exhaust after it hesitated for a few seconds. Together with the flashing CEL I would have suggested engine misfires due to faulty DI, but that was replaced with a working one, and everything was the same (still bad). If we blame it on the TB, perhaps its limiting the air intake, causing unburnt fuel to backfire later in the exhaust? And the CEL is the same, warning of damage to the catalytic converter (which I dont mind, because I dont have one)

I'll try a new TB at my mechanics tmrw morning, although he sounds sceptical.
I've never had a CEL come on
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  #14  
Old 22-07-10
Szmek Szmek is offline
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Ok, well our problems seem to be different, because I'm not losing boost in WOT, just in mid-range throttle. Tmrw morning the mechanic promised to have a TB to swap in to check if it solves the problem. As soon as I know anything more I will post, so as to hopefully help anyone out in the future.

As for now, thank you all for your replies and for those who viewed the thread.
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  #15  
Old 23-07-10
Szmek Szmek is offline
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Quote:
Originally Posted by Idlewild View Post
I have somewhat similar issues, but no CEL yet.
My new throttle body arrives on friday and I think it's gonna cure my problems since there was some faulty cables inside the old TB electronics.
Did your TB arrive today? Did you install it and did it fix your problems?

I spent all day with the mechanic today. Changed the CPS (no change), a few hoses/one-way-valves (no change), unplugged the EVAP hose from the Solenoid valve (no change), and finally switched the TB for a different one (no change)...Still jerking

The last thing we tried, is we plugged the Wastegate hoses from the Solenoid valve. Went for a drive, and the jerkiness disappeared. Nice smooth boost build-up from 2,000rpm. Just that without the wastegate, the turbo was boosting at just over 1.5bars! Really nice, but obviously not the most reasonable option as it will blow my turbo or pistons with prolonged use - but at least it worked for diagnostics. So we're left with the idea that Wastegate actuator is faulty. Tightened the actuator, it was still jerking, but maybe a little less (not really sure). I think the next step is gonna be to replace the Wastegate - probably for a Forge one.

Thats all for now - IDLEWILD, it would be really interesting to see if the new TB fixed your problems (?) because I swapped in a used (not new) TB with no success
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  #16  
Old 23-07-10
Idlewild Idlewild is offline
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Fixed my problems pretty much. Took her for a drive and she's much smoother, the idling is perfect now too. The throttle response is so much better.

If I had a new turbo the car would be perfect now. I also think my vacuum lines and check valves have seen better days since the car has run over 200.000km by now. But there's a project for future days
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Old 23-07-10
Idlewild Idlewild is offline
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Quote:
Originally Posted by Szmek View Post
Did your TB arrive today? Did you install it and did it fix your problems?

I spent all day with the mechanic today. Changed the CPS (no change), a few hoses/one-way-valves (no change), unplugged the EVAP hose from the Solenoid valve (no change), and finally switched the TB for a different one (no change)...Still jerking

The last thing we tried, is we plugged the Wastegate hoses from the Solenoid valve. Went for a drive, and the jerkiness disappeared. Nice smooth boost build-up from 2,000rpm. Just that without the wastegate, the turbo was boosting at just over 1.5bars! Really nice, but obviously not the most reasonable option as it will blow my turbo or pistons with prolonged use - but at least it worked for diagnostics. So we're left with the idea that Wastegate actuator is faulty. Tightened the actuator, it was still jerking, but maybe a little less (not really sure). I think the next step is gonna be to replace the Wastegate - probably for a Forge one.

Thats all for now - IDLEWILD, it would be really interesting to see if the new TB fixed your problems (?) because I swapped in a used (not new) TB with no success
Did you unhook the + cable from the battery between all these changes? Especially when changing the TB it's important to make the car powerless so that Trionic can adapt itself to the values of the new TB.
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Old 28-07-10
Szmek Szmek is offline
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Quote:
Originally Posted by Idlewild View Post
Did you unhook the + cable from the battery between all these changes? Especially when changing the TB it's important to make the car powerless so that Trionic can adapt itself to the values of the new TB.
Yeah, I ended up unplugging the Battery and allowing a ECU reset. Although the car drove nicer with the other TB, the hesitation and jerking was still there.

Just came back from a trip to the seaside (700km/500miles). The car drove good, but had to put my foot down every time to overtake...couldn't do it with half throttle, the jerking/hesitation made it dangerous. Had to really push it - which is kinda silly, when you really don't have to.

Still leaves me with the same problem. Mechanic suggested it could be something to do with the wastegate. Like I mentioned before, when we plugged the hoses to/from the wastegate and solenoid, the problem disappeared (but the amount of boost was just overkill).

If the problem is with the wastegate, could it be the actuator that doesn't know how to set it itself at mid-boost/half-throttle?

or maybe the actual 'waste-gate' on the inside of the turbo (plug/flap) that has deteriorated and doesn't hold (hence the backfires, CEL from damage to the cat?)

Anyone for any ideas?
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  #19  
Old 28-07-10
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Quote:
Originally Posted by Szmek View Post
Still leaves me with the same problem. Mechanic suggested it could be something to do with the wastegate. Like I mentioned before, when we plugged the hoses to/from the wastegate and solenoid, the problem disappeared (but the amount of boost was just overkill).

If the problem is with the wastegate, could it be the actuator that doesn't know how to set it itself at mid-boost/half-throttle?

or maybe the actual 'waste-gate' on the inside of the turbo (plug/flap) that has deteriorated and doesn't hold (hence the backfires, CEL from damage to the cat?)

Anyone for any ideas?
After reading your post, I thought about what my mechanic did. He changed the rod of the wastegate actuator, but I don't know if that counts as 'changing' the actuator. There was an incredible improvement, because my wastegate was stuck opened to begin with. However, I still feel a lot of hesitation after its first use of the day.

When you mention the solenoid, is that when you plug up the top hose?

My mechanic said that he tried to lubricate everything that he can see, but he thinks that the turbo itself needs more exhaust to spool up, hence the hesitation in the beginning, and then the sudden boost after 2900 RPM. So I don't know what to do.

--Michael
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Old 29-07-10
Szmek Szmek is offline
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Quote:
Originally Posted by mfong View Post
After reading your post, I thought about what my mechanic did. He changed the rod of the wastegate actuator, but I don't know if that counts as 'changing' the actuator. There was an incredible improvement, because my wastegate was stuck opened to begin with. However, I still feel a lot of hesitation after its first use of the day.

When you mention the solenoid, is that when you plug up the top hose?

My mechanic said that he tried to lubricate everything that he can see, but he thinks that the turbo itself needs more exhaust to spool up, hence the hesitation in the beginning, and then the sudden boost after 2900 RPM. So I don't know what to do.

--Michael
Well, the suggestion that it is a wastegate problem came from the fact that when we plugged the 'W' hoses from the solenoid valve (the one with 3 nipples sitting next to the intake pipe) and from what I understand this stops the wastegate opening completely. The effect was a smooth boost after pressing down on the throttle (so therefore it fixed the jerking and hesitation issues - boost came in clean and steady from around 2,500-3,000rpm) but the boost was off the scale (literally off the scale on my 1.5bar boost gauge) and even though it was wonderful to feel such power, its either gonna fry my pistons or burn out my turbo! (therefore not really a solution).

Re: hesitation -> I dont mean TURBO LAG. The time it takes for the exhaust fumes to spool the turbo takes some time - but what I'm experiencing is different. I'll try to describe it again for clarity:

Say for example you are in 4th gear cruising at 80km/h (50mph) at around 2,000rpm. You want to overtake, so you press the gas pedal down a bit more, say to about 1/2way. The boost spools up, you get power for a second, but then it stops, like someone plugged up your intake (a choke), a second later it boosts again, then stops.The rpms arent really going up, neither is your speed, and your stuck in a jerking motion, like boosting, then not, then on again. The only thing that helps is either putting your foot down all the way to WOT, then if youre close to 3,000rpm the car takes off normally or downshifting to a gear thats gonna be above 3,000rpm at your speed (in this case 3rd).
But if you're in 5th gear, it keeps jerking, unable to increase its revs above 2,500rpms) until you hear a exhaust backfire (or sometimes a flashing CEL which disappears a few seconds later).

RE: wastegate again. I understand that there is a diaphragm and spring which moves the rod (actuator), perhaps that is the problem - the diaphragm is broken or the spring worn out. But I dont want to spend money on a new Forge one if its not going to solve the problem. Like I said so far, I could have wasted a lot of money on a new DI cassette, a TB and CPS without any solution (God-bless my mechanic for being so kind as to replace these parts and let me test the car to see if its fixed without charging me for them, just for labour).
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