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High Idle After Cleaning Throttle Body


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1999 Infiniti QX4 VG33

 

I cleaned my throttle body because the baffle was sticking harder and harder over the last couple months. After cleaning off the 1/32” of gunk my idle went from 750-850RPM to 1200-1300RPM.

 

With the idle high like is, when I put it in D the vehicle wants to move forward. I have to press the brakes harder to keep from moving forward. Then when slowing down from highway speeds the trans downshifts harder than normal around 45mph. I believe it’s actually the lockup clutch disengaging while still receiving torque from the engine.

 

I can’t figure out how to adjust the IACV under the intake and so I decided to adjust the fast idle which worked well to bring the idle RPM back to the 750-850 range. I marked it so I know where to put it back at if need be.

 

The problem is that when I started the engine earlier the O/D light began flashing for about 10-15 seconds. I am worried that I will somehow damage the trans and that I’ll have to put yet another one in...

 

After adjusting the fast idle the rough downshift/lockup is gone completely, and is actually smoother than ever.

 

Things I have considered:

1. There is a significant vacuum leak that began when I cleaned the throttle body which is the root cause of the high idle.

2. I didn’t allow enough time to let the ECU readjust for the newly cleaned throttle body.

3. I removed enough metal during cleaning (maroon scotchbrite) that the baffle is permanently passing more air and the factory fast idle setting is no longer useful.

 

I’m shooting in the dark with this and need someone to shine a light.

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My '95 didn't idle or shift any differently after I cleaned its throttle body. That was an entirely different computer and a different idle control setup, of course, but I'm still surprised cleaning the TB threw yours off that much. If the vac lines are correct, the throttle body gasket isn't trashed, and the FIC isn't stuck wide open for some reason, maybe someone adjusted yours out of spec to compensate for the dirty throttle body? If that's the case, then it sounds like you're on the right track towards sorting it out. The '97 service manual (I assume '99 is the same) shows a procedure to set the FIC on EC-27, and idle speed/timing/mixture adjustment starting on EC-29.

 

The flashing OD light indicates a trouble code. If it does it again, and you happen to note which flicker is longer, you can decode that using the AT section of the manual. I assume anything that would trigger a code via the old blinky-lights OBD will also set an OBDII code, though, so if you've got an OBDII scanner, just use that. You may have already addressed what it was unhappy about.

I very much doubt you messed up the throttle body that much with a Scotchbrite pad.

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Not if you put it back. Those are generally marked for 1 of 2 reasons: very negative impact on emissions, or having to adjust means something else is very wrong.

I'm not in front of my FSM. I can't remember what FIC stands for. But I don't remember you saying you ran the idle relearn procedure that I am pretty sure is in the FSM.

Sent from my SM-N950U using Tapatalk

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I found it and I’m gonna adjust after the FIC adjustment process.

 

Currently my engine is getting up to temperature. It started off at 1100-1200RPM when I first started the engine but now as it’s heating up the RPM are speeding up. At 170degF it’s at 1500RPM...

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