Question about 1999 Isuzu Rodeo

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Fast Idle Problem With 99 Isuzu Rodeo V6

Had a serious fast idle problem that got progressively worse. Was Idling at 3000rpm! Replaced Idle Control Valve. Idle back down to 750rpm. Turn off ignition. Restart. Idle back up to 1800rpm. OBDII say 0 trouble codes. Disconnected battery to clear computer. No change. Idle 1800rpm. Suspecting cheaply manufactured ICV, replaced ICV again. No change. Idle at 1800rpm. ICV receiving 12V. Pull ICV and adjust plunger. Start car. Idle 750rpm. Turn off car. Restart. Idle 1800rpm. Any suggestions?


Michael in San Diego

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  • Old Suzer Jan 05, 2009

    I haven't started replacing parts yet, but my 1994 Rodeo 5 speed is acting about the same.

    Tom in Spring TX

  • wondermik Feb 25, 2009

    pa_guy12 got it right! I had a fast idle problem. Replaced the idle control valve twice, but the engine still idled at 1700 rpm. I sent the Rodeo to a friend that owns a junk yard and he had his mechanics work on it. They tried replacing the ECM twice! They also replaced the Air Flow Meter. Still, the Rodeo idled at 1700 rpm. I tried pa_guy12's solution of disconnecting the power steering pump pressure sensor and now the Rodeo idles at 750-800rpm!

    Now my new problem is that I can't buy the sensor. The Honda Passport uses a different sensor. Isuzu doesn't sell the sensor separate from the pump. I think this Rodeo will be donated to charity.

    Thanks again,


  • Miguel Ito
    Miguel Ito Aug 21, 2014

    I did it as well and wow... it worked after 4 months with the same trouble. Thanks


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If problem is only on startup and when idleing, then the problem is likely IAC system, also a vacuum leak will cause the same problem.

If problem is not only on startup and idle, but also when driving, then MAP sensor and EGR system must be checked.

Check also accelerator cable state and setting.

Fast Idle Problem With 99 Isuzu Rodeo V6 - 0f04b3c.jpg

The first thing to do is pulling out the OBDII fault codes stored in the ECM. This is done connecting a code reader to the ECM diagnostic port. The job can be done for a small fee at any local garage, and it is done for free at AutoZone.

The codes will help locating the problem.

About possible faults:

Problem is stalling when idling and during startup, but engine idling fast all the time. Problem not starting at times it is due to the fact that the wrong mixture is being sprayed, this is probably causing flooding and misfire. Since the CEL is on, one of the codes returned is probably misfire.

Check accelerator.

Check IAC system. This is composed by a valve and a solenoid that check and control amount of extra air air when the engine is idling. The IAC valve is located on top of the throttle body.

Check the vacuum system and try cranking with gas tank cap off. Vacuum system is tested using an hand tool gauge onvacuum lines while spraying card cleaner on the hoses (or heating them with a torch). If there is a leak, pressure will go up. A big leak will also do hissing noise, and will often result in a lean code when doing an OBD code scanning.

This kind of symptoms can also be caused by weak wiring to MAP/MAF sensor (MAP in this engine).

If the car also drives very rough and is revving up and down in a weird way, check the EGR valve.

As first thing I would do a code scanning. This car is OBDII. The scan can be done for free at the nearest Autozone, or for a small fee at any garage.

If you get any OBDII code from the scan, report it here, so that we can individuate the possible reason for the problem.

If you repute my solution helpful, then please take some times to accept the solution. Providing good repair tips requires time and skills, and your feedback is important for us.



Posted on Oct 26, 2010

  • Miguel N Apr 26, 2013

    I have same problem and finally check engine light is on with code P0101 .99 Honda passport. what would my problem be?


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On the power steering pump is a wire....disconnect it and undo battery for 30 seconds.....see if this fixes it.....the swith in the power steering pump is supposed to bump idle by 200 on full turns....f it shorts it jacks up ilde every time u start truck.

Posted on Feb 15, 2009

  • Eric Stark
    Eric Stark Sep 13, 2015

    Wow! Amazing. Disconnected the power steering pump sensor: fast idle problem SOLVED!


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I have a 2000 Isuzu rodeo. Sometimes the car runs fine and others it is real rough and seems like it is going to die. It feels like a bad hesitation. It has an irradic idle, the reducced power light comes on sometimes. when you go around a corner it dies, sometimes. The car is a v6 . We have replaced the egr valve, the pcs sensor, plugs wires, starter, fuel pump, fuel filter,etc.

Posted on Feb 18, 2009

  • Brent Nonoffyours Apr 23, 2011

    I have the same exact problem. Did you finally fix it and if I may ask what was the problem.


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After changing my idle sensor, throtle position sensor and trying the ECM fuse disconect trick. My idle issues were not resolved. Before looking for an intake manifold leak I did the following, I disconnected the power steering preasure switch and my idle speed has returned to normal. I'm waiting to get a replacement switch for my PS pump. I'll post here with my results.

Posted on Jun 09, 2009

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I am by no means a mechanic but I just had a similar (possibly same) problem in a 2000 f-150. pretty sure mother in law has same problem. I think it could be the intake manifold gasket. I'm reading alot about spraying carb cleaner around manifold in order to find the leak. Vacuum problems will not show up on the vehicles computer, until they cause associated problems. Take it to autozone and ask them to read your vehicles code. Should be free. If no codes, almost definitely a vacuum problem. Seems to be a very common problem on vehicles in that year range.

Good Luck


Posted on Jul 30, 2009

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Fast idle 101: USA CAR???? ill guess that....

first off you never said hot or cold engine?

if hot is it really hot? 180F (or 150) the engine will race if the engine thermostat is bad, and wrong temp. for sure.

if the engine never warms up it will race fast. so...

is it at 180F or more? on this V6 1999 (what size? V6?????)_

if that is ok, fails hot idle.

the next step is knowing the difference between the 2 EFI systems

(to a lay perso,n its MAF or MAP engine)

(makes all the difference that fact)

the MAP engine races for any air leaks (vacuum)

the MAF engines stalls or runs too slow as it goes LEAN.,

see>???????? (illegal air leaks means lean)

EFI controls , basics....

so which is it, ok i open my book. and look.

but wait there are THREE 6v engines. some are TWIN CAM (4 cams total) must i guess that too?

guess what the EFI is not the same on all 3 engines.....dang.

2.6-liter 4ZE1 engine?

3.2-liter 24-valve SOHC V6 (my guess)

3.2-liter V6 up to 194 hp (1996 up graded power)


The 6VE1W 3.5L DOHC 24V V6 was introduced in 1998 with 215 hp (160 kW) and used until 2004

so not saying the displacement , of this v6 is a pain.

ill GUESS its the 2.3L with single cam shaft each bank.

below is my guess on engine and not a guess on WHY.

so how does it race, this engine, in this car.


some cars have both sensors (map/maf) the map is used only at idle and low speeds, and then MAF takes over for more accurate, readings fast.

so we now know that the MAP sensor if it sees any air leaks the engine MUST race with full power, and not go lean.

so what is it.

as posted here the ISC is stuck open

or any vacuum line on car leaking for ANY reasons.

or any PLENUM leaks. for ANY reasons.

or the ISC is dead, because, the ECU sees the idle switch stuck open killing all idle controls. (read TPS errors)

you did the correct thing, unplugging the ISC

ISC ,= idle speed control valve 2 pins is modulated, more is motor drive ISC,. no matter what is there or it NAME.

this causes it to close.

and must not idle so low it stalls.

if NOT , they you just proved, you have vacuum leaks

(the isc can only close 100% and if the engine STILL races

the ECU can not by magic, close the valve more.)


find the leak.

we pinch all hoses to find that first.

and lost more.... some leaks can be hard to find.

propane gas tricks

smoke machines

and more. lots more.

the parts store calls this part the IAC , idle air control

the name is not important.

it is a stepper motor drive, more than 2 pins tells you that.

or close.

getting it to close can be tricky.

one trick i do is to remove it. and pack clay in the port

sealing off all air to this port.

start car with 10% throttle.

then release the throttle , good engines stall now.

if it races it has AIR LEAKs big time, (vacuum leaks)

the engine can not run with no air, so.... there you go.

no air + lots of fuel is flooding.

some cars the ISC closes , unplugged. others not.

others just freeze where they were(steppers)

tricky huh?

on some engines, like this. the map is only there to test the EGR.

i do NOT have intimate knowledge of the PCM on this car.

nor have the very rare FSM books on it.

my guess, as the EGR has read back lines (it does)

the MAP is used at idle. for better calculations of air flow

the MAF work very poor at idle, such low air flow.

my guess based on many EFI systems, worked.

Posted on Sep 14, 2015

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According to Mitchell OnDemand, turn the key on and off after IAC replacement then start. the PCM controld idle speed and is not adjustable.

Posted on Aug 14, 2008

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