Spare DME or ISV
08-19-2018, 10:27 AM
#1
Pro
Thread Starter
Spare DME or ISV
I'm looking to fix my idle issue. It surges between 800 and 1100. I am looking for someone who has a known working spare ISV or DME. I have replaced the transistors on my board, bought a new (used) ISV, have performed all the idle setting procedures and confirmed no vacuum leaks. I'm in the Philly area.
08-19-2018, 05:46 PM
#2
Rennlist Member
I trust you have confirmed that the TPS idle contact is working? Also, quadripple check for vacuum leaks. Pull the plug on the ISV and if it still surges, it's not the ISV. Is it bone stock or do you have a MAF, etc. Some of the aftermarket MAF's had idle issues.
08-19-2018, 09:10 PM
#4
Pro
Thread Starter
This first one shows it, but I was unable to disconnect the ISV.
The second one, I was able to disconnect and reconnect the ISV. You can hear the surge of air when I connect it back up. I did it twice.
The second one, I was able to disconnect and reconnect the ISV. You can hear the surge of air when I connect it back up. I did it twice.
08-19-2018, 09:12 PM
#5
Pro
Thread Starter
Also, did the multimeter test on the idle switch. Works perfectly and consistently. This idle issue is the same as it was before I replaced the transistors on the DME. It only surges when the ISV is connected.
08-19-2018, 09:57 PM
#6
Rennlist Member
I can't quite tell when the plug is on and off the ISV in that second video. Did the surging stop when you pulled the plug of the ISV? Did the system ever idle properly with your m-tune, or did it start when you installed the m-tune?
08-19-2018, 10:04 PM
#7
Pro
Thread Starter
It stopped surging when I pulled the plug off the ISV, but nearly starves the engine from air. As far as I can remember, the idle has never really been stable: M-tune or none. Would cleaning the ISV out with carb cleaner do much?
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08-19-2018, 10:19 PM
#9
Burning Brakes
Do you get the same behavior with the diagnostic jumper wire between point B and C as you do when you physically disconnect the plug from the ISV? Also obvious, but consider double checking the direction of flow arrow on the ISV
08-19-2018, 10:30 PM
#10
Rennlist Member
Did you verify the ISV wire harness connector is not shorted before plugging your repaired DME back in? Those transistors are the fuse for that circuit. If 12V in the wire harness connector shorts directly to either of the other two wires, the ISV solenoid resistance is bypassed & the transistors try to switch way more current than they can possibly handle & poof!
Poor design on Porsche's part not to protect that circuit with a fuse.
Poor design on Porsche's part not to protect that circuit with a fuse.
08-19-2018, 10:41 PM
#11
Rennlist Member
Easiest way to check that the ISV is working is to turn the key on but don't start the engine. Reach in and feel the ISV. If it's vibrating, it and the DME are probably working okay electrically. It could still have an air leak though.