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1G S90 throttle body High idle. Help!!

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Anthony Boni

5+ Year Contributor
213
23
May 13, 2018
Wrightstown, New_Jersey
I can’t figure this out!! It’s driving me crazy. My RPM stays around 1500 only after a WOT pull. If I drive around normally, it doesn’t act up. Only after going full throttle the RPM stays high. I boost leak tested, set the TPS correctly, I’m simulating idle switch using TPS position. ISC motor and FIAV deleted. The throttle cable is not holding the throttle body open. The idle stop screw has no tension on the valve to hold it open. Once I do a WOT pull, I’ll pop the hood and push down on the throttle body valve to make sure it’s fully closed. I don’t know what else to look for.

S90 throttle body by the way!
 
I will be as descriptive as possible here.

Throttle body is closed, RPM surges around 1100-1500 after driving around a bit. Once the car cools down, cold start it and it’s fine. Drive it, same issue.

This is my understanding of what’s happening, correct me if I’m wrong. Being this car is on speed density, I know air has to be getting in somewhere AFTER the throttle body. The ECU sees 0% throttle position, TPS position is .63v, idle switch is active. So the computer knows the car is at idle. But it’s revving higher because of excess air entering. Once it revs higher due to the excess air, the ECU cuts fuel to attempt to maintain target idle RPM. Right?

The FIAV and ISC are still installed on my throttle body, the coolant lines are deleted, the ISC is not plugged in. I’m assuming air is entering in that area, however I can’t find anything on boost leak tests. So I ordered the FIAV block off plate to completely eliminate that section of the throttle body. I re checked base ignition timing again, and it was off. Somehow. I then went into the timing tables in link and lowered timing in idle areas as a last ditch effort to lower my idle. Locked in open loop, car acts the same.
 
Post a log of the activity. Most likely a vacuum leak.
Here is a log of the activity. You can see how high the idle is. I've lowered the FC offset to 0 (It was so high because my car would bog when I first rebuilt the engine it would bog down on coastdown.)
 

Attachments

  • High idle.elg
    617 KB · Views: 83
The FIAV does not have a block off plate installed. I thought it did. I believe there is air bypassing the throttle plate through the FIAV. Hence why during the boost leak test, I see nothing leaking.
 

Attachments

  • E22A2404-3B31-470C-AB7A-5C598C3B5927.jpeg
    E22A2404-3B31-470C-AB7A-5C598C3B5927.jpeg
    1.1 MB · Views: 73
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