Fluctuation RPM issue

Tiny
HANGPRO
  • MEMBER
  • 2002 TOYOTA 4RUNNER
  • 3.4L
  • 2WD
  • 273,000 MILES
I had a bad hesitation problem and sometimes the rpm while driving would surge to 3,000. I installed a new throttle body and intake hoses as well as a new MAF sensor. All OEM Toyota parts. The hesitation is gone and most of the time the engine runs good. But now after warm up and the car sits for an hour or so, It has been hard to start or wont start without really flooring the pedal. Once it starts the RPM's go up to 2500-3000. I turn it off and restart the RPM are normal. Starts fine when cold.
Saturday, September 7th, 2019 AT 1:44 PM

8 Replies

Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello,

This could be a problem with your vehicle's Idle Air Control valve (IAC). This is the valve that lets air around the closed throttle plate when your vehicle is idling or decelerating. Here is a link for you to go to below on how to replace it:

https://www.2carpros.com/articles/how-to-replace-an-idle-speed-control-motor-iac

Please go through this guide and get back to us with how everything turns out.

Thanks,
Alex
2CarPros
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Saturday, September 7th, 2019 AT 2:46 PM
Tiny
HANGPRO
  • MEMBER
  • 5 POSTS
It's my understanding the IAC is built into the throttle body on the 2001 and 2002 4runner. I had a hesitation issue as well so I put a new OEM TB on. So new IAC, MAF, and intake hoses. I don't have the hesitation issue anymore and once the engine is warmed up it rune really good. If it sits for awhile when I start it the RPM are erratic and surgey Once warmed up all good. Don't think I have a vacuum leak. But it seems like a sensor?
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Saturday, September 7th, 2019 AT 3:11 PM
Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello again,

Okay, so believe it or not, the Engine Coolant Temperature (ECT) sensor helps the Power-train Control Module (PCM) determine the ignition timing. If it is being read as wrong(higher temperature) it will retard the timing to bring the engine away from detonation (knock). This could also be the problem. We have testing information available for the ECT if you would like or we have removal and installation instructions if needed as well. Please get back to us if you would like any of the instructions and we will get these right out to you.

Thanks,
Alex
2CarPros
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Sunday, September 8th, 2019 AT 5:10 AM
Tiny
HANGPRO
  • MEMBER
  • 5 POSTS
Thanks. That's what I was thinking. I'm changing the ECT today as well as the PCV.
I'll report back after doing the job with results.
Thanks very much, Phil
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Sunday, September 8th, 2019 AT 8:05 AM
Tiny
HANGPRO
  • MEMBER
  • 5 POSTS
For all folks having hesitation and idle issues here is what I did after a year or more of chasing this problem I believe it is solved:
New throttle body and intake hoses.
New MAF sensor.
New PCV valve.
New ECT sensor.
Replaced a couple of cracked vacuum hoses.
At 273,000 miles I believe replacing these items with OEM new was necessary. Maybe I could have just cleaned the original throttle body but on this year (also 2001) it seemed best to replace the unit.
Engine is running as good as new now! Feel like I just won the lottery. I'm going for another 273,000 miles.
Thanks for the assistance 2CarPros!
Phil
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Monday, September 9th, 2019 AT 8:25 AM
Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello again,

That is what we like to hear!

Thanks.
Alex
2CarPros
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Monday, September 9th, 2019 AT 8:31 AM
Tiny
HANGPRO
  • MEMBER
  • 5 POSTS
Now I need to replace the radiator. Top seam is leaking. Fun stuff!
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Monday, September 9th, 2019 AT 10:31 AM
Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello again,

Yes sir, been there and done that. Sometimes it seems like when it rains, it pours. Do you need instructions on how to do that or do you have it covered?

Thanks,
Alex
2CarPros
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Tuesday, September 10th, 2019 AT 9:10 PM

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