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  #1  
Old 12th December 2008
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Default Strange Idle

Car:
1988 900S (bone stock)

Problem:
-When cold, the car idles at no less than 1000rpm.
-When warm, it idles around 1400. On a good day it will stick to 1200.
-When hot, or after running errands (starting the car, turning the car off, starting again, etc), it will raise from 1400 to 1600, and then rapidly fall back to 1400 where it will once again climb back up. Once cycle of this takes about a second or two.

Attempted Fixes:
-AIC thoroughly cleaned out
-Checked for vacuum leaks
-Checked Throttle position sensor


So, any ideas? Thanks for the help.

David
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  #2  
Old 12th December 2008
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Which injection system do you have? If it's LH2.2, you might want to investigate the air mass meter. Townsend has a good page of diagnosis for this.

http://townsendimports.com/Web/tuneup_folder/amm.htm
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  #3  
Old 12th December 2008
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I have an '89 900 S (bone stock also). My car was doing something similar to yours...except my idle would run high and then fall well below normal. When cold, the idle was fine...the engine would turn on with no problem and it was steady.

When the engine was warm, the idle and start-up would be very temperamental.....idle would go up and down, from around 1500 to almost dying and sputtering. When trying to start a warm engine, it would start for a second and then die often as well.

My indie took the same steps you did....cleaned the AIC, injected smoke to check for vacuum leaks, etc. The problem turned out to be the fuel pressure regulator. Once replaced, the problem went away.
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Old 12th December 2008
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thank you both. i'll see about finding an FPR and AMM to test with. hopefully it's just the FPR.... i don't have the money for an AMM!
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Old 12th December 2008
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Quote:
Originally Posted by SwimDude0614
thank you both. i'll see about finding an FPR and AMM to test with. hopefully it's just the FPR.... i don't have the money for an AMM!
Don't even bother with the FPR
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  #6  
Old 12th December 2008
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Quote:
Originally Posted by 900t
Don't even bother with the FPR
huh??? if i can find another FPR, that's a quick and easy check.
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Old 12th December 2008
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Quote:
Originally Posted by SwimDude0614
huh??? if i can find another FPR, that's a quick and easy check.
Actually try running it with the AMM unplugged (limphome) that one is really fast
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Old 13th December 2008
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I would be scrutinising the ground leads.........

near the thermostat..... - may not be the direct cause but I have seen subtle improvements in my car afterwards. Check the valve cover breather (integral part of idle path), esp. the small tap at the top. It gets clogged.
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  #9  
Old 13th December 2008
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can i unplug the amm while the car is still running or should i turn it off before plugging in or unplugging everytime?
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  #10  
Old 13th December 2008
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Default Quick Test:

Test: Unplug and replug AMM

Temp: Normal operating temp

Before: idled steadily at 1400 rpm

After AMM is unplugged: Rapidly jumped between 1100 and 1200

After plugging the AMM back in: Rapidly jumped between 1500 and 1900

I then turned the car off, got back in, and drove into the driveway. At this point it returned to it idling at a steady 1400rpm.

Pehaps I missed a vacuum leak? It seems like all my readings are a little higher than everyone else's.
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  #11  
Old 13th December 2008
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Quote:
Originally Posted by Rodentmaster
Check the valve cover breather (integral part of idle path), esp. the small tap at the top. It gets clogged.
I highly recommend this suggestion.

Also clear out the semi-clear plastic valve connecting two vacuum lines near the breather...remove this and spray it out I,ll bet your idle settles...it does get clogged easily.
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  #12  
Old 13th December 2008
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Quote:
Originally Posted by stickman
Also clear out the semi-clear plastic valve connecting two vacuum lines near the breather...remove this and spray it out I,ll bet your idle settles...it does get clogged easily.
i'll check the breather as soon as i type this.

what is this semi-clear valve you're talking about though? can you take a picture?

-Edit-
Thanks! I cleaned both the transparent breathers atop the intake manifold - the one closer to the firewall was FILTHY. propably clogged. the carb cleaner came out black for about a minute before it finally got clean. off to go drive now...

-Edit #2-
Just finished throwing her around the streets pretty hard (that's what usually makes it sputter) and she did fine. still idles up at 1400 when warmp, but the sputter is gone
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Last edited by SwimDude0614; 13th December 2008 at 03:56 PM.
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  #13  
Old 14th December 2008
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well, turns out it was the the throttle position sensor. guess i threw you all off a little when i said i checked it. by "checking" it, i meant it was placed correctly. of course... it doesn't do much good if it's broken.

if anyone reading this has one used that they're willing to sell cheap, let me know. otherwise, i know where to buy them new.
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  #14  
Old 7th April 2009
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I was wrong. It is not the throttle position sensor. After unplugging it, the idle did not change. I thought that was the problem. After using an ohmeter to TEST it, i found out i was wrong. the TPS is working perfectly.

so, next idea, O2 sensor. i snapped the wires to the O2 sensor by accident when working on the exhaust and yet again, NO change in idle at all. (before this, i got 22mpg when driving like a grandma around town on a darky rainy night. in the snow. uphill. both ways )

new thought: scary thought... if disconnecting the TPS did nothing to change the idle, even though it was working, is it possible my O2 sensor is (was) working correctly too and the ECU is busted? although, disconnecting the AMM does change idle and makes it run terribly
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  #15  
Old 15th July 2009
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I've now added some more things that are NOT wrong with the car. Sunday, I replaced (one at a time) the air mass meter and AIC valve with no luck.

on the other hand... i think i fixed it!!!
i was showing my gf how to drive a stick and when we were all done, i decided to be all cool and such and i did a burn out in the parking lot. after that, car ran great. immediately after that. and for the rest of the day too!!!! I haven't driven today yet though. before burn-out: idle jumping between 1600 and 1900 like i said in the first post. after burn-out: idle steady at 1000.

so apparently, my car is just tired of being driven like a grandma car (i typically go for gas mileage while driving). i think maybe if i do another burn out, my busted headlight brackets will automatically readjust themselves
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Old 15th July 2009
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don't do burnouts just drive at WOT on some backroads to 120 mph or whatever (okay you don't need to do that much unless you know the police are at the donut shop)
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Turbo allows the valiant who has appeared at the wheel SAAB to gain momentum for 200 km/h Charm SAAB Turbo also that it to you not bad Porsche on it it is possible with speed of pregnant turtle feeling itself in full comfort which by the way our hero obeys a rudder reliably and confidently the truth management hardly will twirl a steering wheel by one finger uneasy. Without the hydraulic booster quickly enough perishes a steering shaft, but to change its hemorrhoids from the most fierce
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  #17  
Old 15th July 2009
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so our cars really do need to be thrown around from time to time? i never put less than 91 octane fuel in the car (93 when available) and i thought just so long as i kept the right fuel in there it would be fine.
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  #18  
Old 15th July 2009
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In my experience, no... that said I drive relatively hard. It's fun though

I don't know why you would bother with premium on a non-turbo model, put the 87 she won't mind :P
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Turbo allows the valiant who has appeared at the wheel SAAB to gain momentum for 200 km/h Charm SAAB Turbo also that it to you not bad Porsche on it it is possible with speed of pregnant turtle feeling itself in full comfort which by the way our hero obeys a rudder reliably and confidently the truth management hardly will twirl a steering wheel by one finger uneasy. Without the hydraulic booster quickly enough perishes a steering shaft, but to change its hemorrhoids from the most fierce
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  #19  
Old 16th July 2009
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when i had the 2.1L, i had terrible knocking anytime i put less than 91 in. turbo has lower compression AND a wastegate - after reading through the bentley, i thought the turbo models were the ones that didn't need higher octane fuel?
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Last edited by SwimDude0614; 16th July 2009 at 12:33 AM.
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  #20  
Old 16th July 2009
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Have you checked for a ruptured vacuum advance module on your distributor?
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