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Low idle issue while in drive

Tiny
EALBA27
  • MEMBER
  • 2010 TOYOTA TACOMA
  • 4.0L
  • V6
  • 2WD
  • AUTOMATIC
  • 130,000 MILES
I have recently changed the MAF sensor and throttle body, spark plugs are fairly new and coil packs are fine. I have a new battery and alternator installed and I still have low idle while in drive at about 550 RPMs. I don’t think that this generation have IAC and I have checked all hoses and there isn’t any vacuum leaks. What would be the next best step in trying to troubleshoot that problem? It idles fine on park and neutral and with the A/C is a little better but with no A/C in drive it only idles to 550 RPMs?
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Thursday, September 9th, 2021 AT 6:54 AM

10 Replies

Tiny
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  • MECHANIC
  • 6,383 POSTS
Hello,

The typical idle speed for these trucks with the 4.0 V6 engine is 600-750 RPMs.
So your idling speed is just about the average for these trucks.

Now are you experiencing rough idle?
Or did it idle higher before and all of a sudden dropped?
Or any other drivability issue?

Let me know.
Thank you.

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Thursday, September 9th, 2021 AT 7:51 AM
Tiny
EALBA27
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  • 6 POSTS
Hello, it would idle at about 675-720 RPMs under load/drive without the A/C on. I have to have the A/C on for it to be in range to idle while in drive when pressing the brakes at a stop. The regular idle is fine when in neutral or park is fine. It only goes down when I’m drive and pressing the brakes at a stop.
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Thursday, September 9th, 2021 AT 8:10 AM
Tiny
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So when you put it in drive does it seem to bog down? Does it idle rough?
Is it throwing any trouble codes?
Did this low idle under load just started all of a sudden? Or did it slowly go down over time?
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Thursday, September 9th, 2021 AT 8:22 AM
Tiny
EALBA27
  • MEMBER
  • 6 POSTS
It does bog down a bit, and remains at a low idle, it does idle rough when I’m on the brake for awhile (example; in traffic jam). It doesn’t have any codes and check engine light never appeared. Yes, it did start all of sudden.
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Thursday, September 9th, 2021 AT 8:25 AM
Tiny
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Since it is not throwing a code it is difficult to diagnose issues of this subtle nature.
This could be due to a calibration issue with the throttle body. If the resistance value is off then it can impact the idle speed. As this is a drive by wire, there is no manual adjust like the cars of the past.
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Friday, September 10th, 2021 AT 2:14 PM
Tiny
EALBA27
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  • 6 POSTS
I had replaced the throttle body awhile ago, and figured that might have been the issue and used the warranty to get a new one and it’s still doing the same thing. I’ll check the calibration with an ohmmeter and see if it’s off.
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Friday, September 10th, 2021 AT 2:21 PM
Tiny
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Let me know what you find.
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Friday, September 10th, 2021 AT 2:40 PM
Tiny
EALBA27
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  • 6 POSTS
The calibration was fine, now the problem is the RPMs drops pretty low to only 550 RPMs when I press the brake pedal while in drive and it’ll pop up for like 5 seconds and go back down to around 500 RPMs. If I let go of the brake pedal it’ll go back to normal range. I have no codes. Could it be a shortage? The idle is now fine in drive or neutral regardless if A/C is turned on or off.
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Tuesday, September 21st, 2021 AT 10:19 AM
Tiny
EALBA27
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  • 6 POSTS
The calibration was fine, now the problem is the rpm drops pretty low to only 550 rpm when I press the brake pedal while in drive and it’ll pop up for like 5 seconds and go back down to around 500rpm if I let go of the brake pedal it’ll go back to normal range. I have no codes. Could it be a shortage? The idle is now fine in drive or neutral regardless if A/C is turned on or off.
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Tuesday, September 21st, 2021 AT 10:19 AM
Tiny
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Usually when the RPM drops when depressing the brake pedal, it points to a vacuum leak. As you have to use the brake booster vacuum to operate the brakes.
Most of the time, when the throttle actuator is faulty it will trigger the check engine light.
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Tuesday, September 21st, 2021 AT 10:14 PM

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