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Discussion Starter #1
SilverSaab runs fine but has one oddity: With cruise control on and trying to keep the speed at the right level, it surges up and down. That is, it seems to accelerate a little too much to return to speed when heading up an incline and then it will back way off when you head downhill. OTOH, if I just keep my foot on the throttle and manually maintain a steady speed, it's solid as a rock. In fact, I will need very little throttle variation to stay steady manually while the CC will do the large amounts.

I noticed it as a g-force issue. Not that it's that huge, but I could feel the car surging. I started to watch the "turbo" gauge and I could see it heading up or down to match the surges. It stays in the green zone, but it heads too high and it drops way too low.- If I turn on the cruise and keep my foot steady on the throttle anyway, the surge dissipates. So it's clearly the ECU adjusting the throttle plate incorrectly.

- I replaced plugs, air filter, and small vac hoses. No changes.
- I swapped a MAF from a car that didn't have this issue. No change.
- I have a Stage-1 Mike D tune but the problem occurs with the stock ECU too.
- No CEL's or pending codes. I don't have a Tech II for other codes.
- It's not ambient temp affected.
- I haven't swapped the DIC. I can, I have plenty, but I don't see any indication that it's a DIC like issue.

Any ideas? Anyone seen anything like this before? The tune gives me access to Open SID, so if there's something there that might help me find the issue, let me know. I don't really understand much that's in there.
 

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In my openSID (and there are differences between versions), Cmem is the set cruise speed in km/h. Is that static when cruise is engaged? Mine is, regardless of actual speed.

Pgsi seems to be a indication of how much the engine is varying power, to maintain Cmem. It varies of course, and don't know what units Pgsi uses.

What happens with a constant gradient to these two parameters (if indeed they are the same in your openSID as mine)?

Doug
 

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Discussion Starter #4
Throttle housing feedback potentiometers worn.
I was thinking TB too, but I don't get any codes. Do you think they could be worn without throwing codes? Also, this car only has 60K miles... seems low for TB issues (but perhaps it's just corrosion on the potentiometers?)



In my openSID (and there are differences between versions), Cmem is the set cruise speed in km/h. Is that static when cruise is engaged? Mine is, regardless of actual speed.

Pgsi seems to be a indication of how much the engine is varying power, to maintain Cmem. It varies of course, and don't know what units Pgsi uses.

What happens with a constant gradient to these two parameters (if indeed they are the same in your openSID as mine)?

Doug

Thanks, Doug. I will look at those params and see what I get for numbers.



FWIW - Some more observation today showed me that I get the surge happening even when maintaining speed on the flat. It swings from 3/4 green on the turbo gauge to nearly the bottom, and then back again within three to ten seconds (repeatedly).
 

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Hey BobSaabit,
Sorry to resurrect an old thread, did you ever diagnose the problem? I have a similar issue on my 1999 Viggen, I was curious if you had come to a solution / root cause to the issue?
Thanks!
 

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I feel like this isn't going to help, but when I bought an '04 9-5, it had the exact surging thing on cruise that you're describing. It also had a stage 1 tune, but not sure from where. Open SID too

I replaced the vacuum lines, thermostat, air filter, spark plugs, DIC, serpentine belt. I don't think the surging went away. I then gave the car to my mother cause she needed it. A couple months later, after they had put $1k-2k in it in new tires, whole new exhaust (I THINK that was the only thing mechanical), the surging is no longer there.

So....exhaust maybe? I don't wanna point you in the wrong direction, but that's just what I noticed
 

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Discussion Starter #7
I was fairly comfortable with Mimmi's suggestion that the problem was the TB. I had a spare lined up, but unfortunately it ended up in my other car, so I never did a swap. So, the short answer is that I didn't cure it, but I'd still head that way as I think it makes sense.
 

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My 2002 does this on occasion, and everything I have read points to the TB. Don't quote me on that, and I haven't replaced it yet at 95K. My car also starts like crap when cold, maybe a rebuild might help with that, but I doubt it. I have the typical... Start car, fires right up, idles great for about 10 seconds, then stumbles and dies or stumbles/mis-fires. 30 seconds later its fine. I think its probably the FP/check valves as they are org.
 

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Discussion Starter #9
My 2002 does this on occasion, and everything I have read points to the TB. Don't quote me on that, and I haven't replaced it yet at 95K. My car also starts like crap when cold, maybe a rebuild might help with that, but I doubt it. I have the typical... Start car, fires right up, idles great for about 10 seconds, then stumbles and dies or stumbles/mis-fires. 30 seconds later its fine. I think its probably the FP/check valves as they are org.
Never heard of a FP doing that. I can see possibilities but it's not a common condition, for sure. Is your CPS old?
 

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Cps is a year old, same with DIC. Its weird one for sure, but it seems to be pretty common if you search. Some have fixed with FP, some not. Same goes with DIC, CPS, Vacuum, etc. There doesn't seem to be anything that points specially to this issue from what I have read. And since everything else has pretty much been replaced, hmmmm. I don't know, I live with it now and have been for years.
 
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