Fluctuation RPM issue

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.

8 Replies

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

SPONSORED LINKS

Was this

answer

helpful?

Yes

Saturday, September 7th, 2019 AT 2:46 PM

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?

Was this

answer

helpful?

Yes

Saturday, September 7th, 2019 AT 3:11 PM

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

Was this

answer

helpful?

Yes

Sunday, September 8th, 2019 AT 5:10 AM

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

Was this

answer

helpful?

Yes

Sunday, September 8th, 2019 AT 8:05 AM

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