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Stumble at idle only???

839 views 6 replies 3 participants last post by  nova7sec 
#1 ·
I am trying to cure this problem on a 1998 900 2.o turbo. It has 90k on the clock and runs great. It has been meticulously maintained but has developed a problem that seems to be difficult. Cold or Hot, intermittantly after you come to a stop and have it in gear, about 8 seconds later it stumbles and quickly recovers. It does this two or three times in a row and then runs fine until the next stop. Sometimes it will completely shut off. We have replaced plugs, DI casette, crank sensor, map sensor, cleaned the Idle air valve and throttle body. The fuel psi stays constant at 44psi while all of this happens. Any thoughts?

matt;oops:
 
#2 ·
check the large hose going to the brake master cylinder. If it's loose, it will definitely cause your car to stall at a stop.
 
#3 ·
I will check that out in the morning as it is raining here today. Most of the time it idles perfectly and then all of the sudden stumble stumble. The Idle air valve compensates and the idle raises to 1000 rpm or so, after recovery it idles perfectly again... until the next time
Thanks
Leon said:
check the large hose going to the brake master cylinder. If it's loose, it will definitely cause your car to stall at a stop.
 
#5 ·
So maybe stumble is not the right word. I have checked for vacuum leaks and can't find one. I have created vacuum leaks intentionally and it still runs smooth. When it.... stumbles/missfires/shakes/stalls it is violent as if two or more cylinders cut out for a second or two. Then it recovers and runs fine again... until ten or so seconds where it does it again... then runs fine for hourrs..... help......
earthworm said:
 
#6 ·
Remove and reinstall the DI cassette again.

Who did this the last time ?

Spend minutes rather than seconds doing the operations - examine everything. As a DIY you can afford to to this; a pro cannot, but is the pro an absolute perfectionist in everything that he does ?
 
#7 ·
So another day of saab tastic results. So I did redo the DI cassette and same thing. I was playing around and found that the turbo bypass valve was not opening at idle as it is supposed to. And also as I revved the engine positive pressure came out the vacuum port. This letting me know that the diaphram was no good. I replaced it and now the car is different. It surged up instead of down???? what the heck? Lastly I checked the purge valve. It sticks, so replaced it and today for the first time in a long time no stalling, no surging, no problem. So can someone explain that....
earthworm said:
Remove and reinstall the DI cassette again.

Who did this the last time ?

Spend minutes rather than seconds doing the operations - examine everything. As a DIY you can afford to to this; a pro cannot, but is the pro an absolute perfectionist in everything that he does ?
 
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