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Join Date: Aug 2013
Posts: 933
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ISV issue or not?
My ISV is over 25 years old on "whitey" and I am looking to replace it since I have already replaced the hoses to it and still find my idle dipping below 800rpms when coming to a stop.
The idle is good @ 900/950 when the car is warm, but the above still happens when stopping at lights, stop signs, etc etc. I have replaced all of the vacuum lines in the engine bay, used zip ties on the ends to keep everything snug, and did the intake gaskets last winter when resealing the cam box, foes, and replaced all of the coolant hoses and clamps, and isv hoses/clamps. Am I barking up the wrong tree by thinking my ISV is still to blame for the drop in rpms? instead of spendng $275 on a bosch isv, what are you thoughts on this cheapie Last edited by fiily; 08-15-2015 at 04:12 PM.. |
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Registered User
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I would do plugs, wires and oxygen sensor first.
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1987 944 Summer 2006 E90 Winter |
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Join Date: Feb 2001
Location: Buzzards Bay, Ma, USA
Posts: 620
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With the ignition on and the engine off so it is quiet you should be able to hear the ISV humming and feel it vibrating. There is also a bench test where you apply low voltage to the unit and you can see it move. Sometimes a good cleaning will help. Try this before you replace anything. Search this site for more information.
Idle Valve I used a knockoff brand as a replacement 3 months ago with good results so far. Jon
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87 924S 82 924-Gone. 80 924 parts car-Gone. |
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Join Date: Aug 2013
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New cap, rotor, plugs....o2 sensor, probably the original. Going to pull the trigger on the isv, $35 part, and look into replacing the o2 sensor.
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Quote:
It could be your throttle position sensor/switch is loose or out of adjustment, too. |
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Join Date: Feb 2003
Location: SF East Bay
Posts: 1,856
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It takes a fraction of a second for the DME to activate ISV and adjust idle-speed when you let off throttle. If you have 80/20 throttle-bypass/ISV to supply idle-air, that 20% supplied by the ISV will have a slight delay. Very easy to fix by removing ISV from warmed-up idle.
1. Disable ISV with jumper 2. set idle-screw in throttle-body so idle is 950rpms 3. enable ISV This mechanically sets idle-air volume to 950rpms with no supplementation by ISV (100/0). All idle-air is through throttle-bypass and when you let up throttle, ISV is not needed to "catch" the dropping engine-speed. |
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Join Date: Aug 2013
Posts: 933
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Quote:
I did the idle reset 2 weeks ago, and idle is fine and is pretty much between 900-950. It's only when coming to a stop I notice the rpms drop below 900, like a blip then the car jumps back up to 9--950 rpms. Stumped a little here |
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Join Date: Feb 2003
Location: SF East Bay
Posts: 1,856
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I notice sometimes, the ISV doesn't fully close when you jumper it. As a result, it still contributes to idle air. In these cases, i take out the ISV and plug up the hoses. Then I set idle-speed and re-install the ISV.
There is also a fuel-cut & RPM setting in the chip where it's turned back on. But that only affects the early cars. Third-party idle-valves can work. Make sure the impedance matches the factory one. There are some with lower impedance that may overheat the DME driver transistor. |
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Join Date: Apr 2015
Posts: 94
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Hi,
First for a quick test I would.... Warm up the car. Jumper B to C on the diagnostic connector. Adjust the idle to 900 +/-50 (I set mine for 850) Keep the jumper on. Go for a drive and see what happen. Make sure the AC is off. The car should not need the idle stabilized in this condition and should idle well. If it does not I would start looking some place other then the idle valve. Peter |
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