Pajero, 2001 3500 V6, rough engine at high RPM

Idle speed depends on a number of factors; for instance it may idle faster when the air conditioner is on. Instead of a fixed idle speed, as in the old cars, the engine computer sets the speed to whatever is needed to run any accessories and maintain smooth operation, but generally not more than that. That's under normal circumstances. There are several failure modes that cause erratic idle speed; usually the engine will also run roughly.

Replace the air filter and IAC idler air control valve.

It can be issue with IAC( idle air control valve) causing the problem.

There are many other possibilities causing these idle issues.Engine idles rough.

There are few help links with solutions to troubleshoot such idle issues.

I suggest you refer the link below and follow its troubleshooting details:------

Click the link below:-----
Bad miss at idle? http://technoanswers.blogspot.com/2012/01/bad-miss-at-idle.html

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Stumbling and stalling at idle after engine rebuild?

http://schematicsdiagram.blogspot.in/2012/03/stumbling-and-stalling-at-idle-after.html

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1999 Ford F-150 Idles rough and quits when gas pedal is pressed less?

http://technoanswers.blogspot.in/2012/01/1999-ford-f-150-idles-rough-and-quits.html

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Engine stumbles coming off idle when warm?

http://repairhelpcenter.blogspot.com/2012/01/engine-stumbles-coming-off-idle-when.html

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Erratic idle on car?

http://schematicsdiagram.blogspot.com/2011/12/erratic-idle-on-car.html

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Cold start problem and vehicle shudder around 2500 to 3500 rpms
http://repairhelpcenter.blogspot.com/2012/10/cold-start-problem-and-vehicle-shudder.html

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Low idle when cold out side?

http://repairhelpcenter.blogspot.com/2011/12/low-idle-when-cold-out-side.html

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GMC Sonoma Stalls and idles low

http://technoanswers.blogspot.com/2012/10/gmc-sonoma-stalls-and-idles-low.html

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GMC Idle Air Control (IAC) Valve Replacing?

http://schematicsdiagram.blogspot.com/2011/12/gmc-idle-air-control-iac-valve.html

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1996 Camry intermittent engine failure while idle?

http://repairhelpcenter.blogspot.com/2011/10/1996-camry-intermittent-engine-failure.html

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Engine quits at idle?

http://repairhelpcenter.blogspot.com/2011/10/engine-quits-at-idle.html

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Car overheats and Air blows hot at idle?

http://howtobyme.blogspot.com/2011/11/car-overheats-and-air-blows-hot-at-idle.html

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High Idle Problem

http://repairhelpcenter.blogspot.com/2012/10/high-idle-problem.html

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While stop engine idles like cylinder missing?

http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html

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Idle flair is noticed on car? Rough idle? car will not idle? Erratic idle speed?

http://technoanswers.blogspot.in/2012/02/idle-flair-is-noticed-on-car-rough-idle.html

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High rpm in neutral? Inconsistant high RPM in neutral?

http://technoanswers.blogspot.in/2012/02/high-rpm-in-neutral-inconsistant-high.html

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Vehicle stumbling at idle and shows code 54?

http://schematicsdiagram.blogspot.in/2012/03/vehicle-stumbling-at-idle-and-shows.html

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Rough idle, staling and Erratic shifting?

http://technoanswers.blogspot.in/2012/03/rough-idlestaling-and-erratic-shifting.html

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While stop engine idles like cylinder missing?

http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html

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These details will help.

Thanks.

Check out related help links to troubleshoot these problem:----Click the link below:---Idles Fine but RPM jumps in drive mode? http://technoanswers.blogspot.in/2012/07/idles-fine-but-rpm-jumps-in-drive-mode.html
---------Mitsubishi Lancer rpm needle bounces? http://technoanswers.blogspot.in/2012/02/mitsubishi-lancer-rpm-needle-bounces.html
--------How to adjust rpm on 2009 dodge charger SRT8?

http://schematicsdiagram.blogspot.com/2011/12/how-to-adjust-rpm-on-2009-dodge-charger.html
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Engine cuts out at 3000 RPM? http://schematicsdiagram.blogspot.com/2011/12/engine-cuts-out-at-3000-rpm.html

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Cold start problem and vehicle shudder around 2500 to 3500 rpms
http://repairhelpcenter.blogspot.com/2012/10/cold-start-problem-and-vehicle-shudder.html

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High rpm in neutral? Inconsistant high RPM in neutral? http://technoanswers.blogspot.in/2012/02/high-rpm-in-neutral-inconsistant-high.html

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Jetski Sputters and Low RPM? http://whatisbyme.blogspot.in/2012/07/jetski-sputters-and-low-rpm.html

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Fuel Injection Problem And RPM suddenly increases http://whatisbyme.blogspot.in/2012/07/fuel-injection-problem-and-rpm-suddenly.html

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2005 Toyota Highlander: Engine runs hard RPM below 3000? http://whatisbyme.blogspot.in/2012/05/2005-toyota-highlander-engine-runs-hard.html

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1987 Toyota Camry: RPM Drops going Up hills? http://whatisbyme.blogspot.in/2012/05/1987-toyota-camry-rpm-drops-going-up.html

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Cruise Control stops working, Excessive cranks to start the engine and RPM goes max 2500 http://whoisbyme.blogspot.in/2012/07/cruise-control-stops-workingexcessive.html

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1990 Toyota 4Runner: Engine cuts off when reaches 2000 RPM?

http://whatisbyme.blogspot.in/2012/05/1990-toyota-4runner-engine-cuts-off.html

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1999 Toyota Camry: Erratic stalling and high engine RPM at idle?

http://whatisbyme.blogspot.in/2012/05/1999-toyota-camry-erratic-stalling-and.html

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1995 Toyota LS: Misfire at idle or low RPM http://whatisbyme.blogspot.in/2012/04/1995-toyota-ls-misfire-at-idle-or-low.html

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Lexus RX: Tapping noise under Valve Cover At Low RPM? http://technoanswers.blogspot.in/2012/04/lexus-rx-tapping-noise-under-valve.html

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These will help.
Thanks.

Check out related help links to troubleshoot these problem:----Click the link below:---Idles Fine but RPM jumps in drive mode?http://technoanswers.blogspot.in/2012/07/idles-fine-but-rpm-jumps-in-drive-mode.html
---------Mitsubishi Lancer rpm needle bounces?http://technoanswers.blogspot.in/2012/02/mitsubishi-lancer-rpm-needle-bounces.html
--------How to adjust rpm on 2009 dodge charger SRT8?

http://schematicsdiagram.blogspot.com/2011/12/how-to-adjust-rpm-on-2009-dodge-charger.html
---------
Engine cuts out at 3000 RPM?http://schematicsdiagram.blogspot.com/2011/12/engine-cuts-out-at-3000-rpm.html

---------

Cold start problem and vehicle shudder around 2500 to 3500 rpms
http://repairhelpcenter.blogspot.com/2012/10/cold-start-problem-and-vehicle-shudder.html

---------
High rpm in neutral? Inconsistant high RPM in neutral?http://technoanswers.blogspot.in/2012/02/high-rpm-in-neutral-inconsistant-high.html

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Jetski Sputters and Low RPM? http://whatisbyme.blogspot.in/2012/07/jetski-sputters-and-low-rpm.html

--------
Fuel Injection Problem And RPM suddenly increaseshttp://whatisbyme.blogspot.in/2012/07/fuel-injection-problem-and-rpm-suddenly.html

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2005 Toyota Highlander: Engine runs hard RPM below 3000?http://whatisbyme.blogspot.in/2012/05/2005-toyota-highlander-engine-runs-hard.html

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1987 Toyota Camry: RPM Drops going Up hills?http://whatisbyme.blogspot.in/2012/05/1987-toyota-camry-rpm-drops-going-up.html

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Cruise Control stops working, Excessive cranks to start the engine and RPM goes max 2500 http://whoisbyme.blogspot.in/2012/07/cruise-control-stops-workingexcessive.html

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1990 Toyota 4Runner: Engine cuts off when reaches 2000 RPM?

http://whatisbyme.blogspot.in/2012/05/1990-toyota-4runner-engine-cuts-off.html

------------
1999 Toyota Camry: Erratic stalling and high engine RPM at idle?

http://whatisbyme.blogspot.in/2012/05/1999-toyota-camry-erratic-stalling-and.html

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1995 Toyota LS: Misfire at idle or low RPMhttp://whatisbyme.blogspot.in/2012/04/1995-toyota-ls-misfire-at-idle-or-low.html

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Lexus RX: Tapping noise under Valve Cover At Low RPM?http://technoanswers.blogspot.in/2012/04/lexus-rx-tapping-noise-under-valve.html

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These will help.
Thanks.

For this types of problem,there are few help inks to troubleshoot the problem.Click the link below to go through the troubleshooting procedure to resolve the issues :----Idles rough and quits when gas pedal is pressed less? http://technoanswers.blogspot.in/2012/01/1999-ford-f-150-idles-rough-and-quits.html-----------van idles rough? http://howtobyme.blogspot.in/2012/01/2004-ford-freestar-van-idles-rough.html
--------------runs lean and idles rough? http://technoanswers.blogspot.in/2012/02/ford-runs-lean-and-idles-rough.html
-----------Car still runs Rough after tune up? http://howtobyme.blogspot.com/2011/12/car-still-runs-rough-after-tune-up.html
------------Idle flair is noticed on car? Rough idle? car will not idle? Erratic idle speed? http://technoanswers.blogspot.in/2012/02/idle-flair-is-noticed-on-car-rough-idle.html
----------High rpm in neutral? Inconsistant high RPM in neutral? http://technoanswers.blogspot.in/2012/02/high-rpm-in-neutral-inconsistant-high.html
------------Engine Backfires? http://technoanswers.blogspot.in/2012/02/jeep-backfires.html----------- Nissan stalls and bucks on Acceleration?

http://technoanswers.blogspot.in/2012/02/nissan-pathfinder-stalls-and-bucks-on.html

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Nissan Pathfinder Backfires? http://technoanswers.blogspot.in/2012/02/nissan-pathfinder-backfires.html
---------How to adjust rpm? http://schematicsdiagram.blogspot.com/2011/12/how-to-adjust-rpm-on-2009-dodge-charger.html
------------Engine cuts out at 3000 RPM? http://schematicsdiagram.blogspot.com/2011/12/engine-cuts-out-at-3000-rpm.html
----------This will help.Thanks.

check automatic idle speed motor if equipped.

Vacuum leaks. Check all hoses and intake bolts. Leaking EGR or plugged PCV valve. Air filter plugged. Leaking head gasket. Worn timing chain. Camshaft lobes worn. Valves burned or leaking. Fuel idle control system or sensor. Good luck!

Common issue at the shop (i'm a ford technician), here is what I do to correct it.
Here is the most common cause of surges and stalls at stops and low erratic idle speed and rough idle, it is the idle speed control air-bypass valve and throttle valve (IAC for short), they get full of gunk over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.