High Idle petrol 120

[Jon Avid PP Poster! Find all posts View Profile Close Jon]

I have a petrol 2009 120 GXL manual Prado.
The problem that I have is where the idle speed will sit at about 1200RPM until the vehicle stops, then the idle drops to normal idle about 750RPM.
The vehicle will sit at about 40KM/H in 4th gear on a flat road with no pressure on the accellerator pedal.
Toyota have replaced the throttle body with no difference and then said there was no problem as there was no faults showing on the computer.
I checked the MAF sensor and found it out of spec. Toyota checked and found it slightly out, and replaced it, had slight improvement, now sits at 1100RPM.
This makes for interesting 4WD'ing down steep hills!
As Toyota has indicated that there is no problem, does anyone have any idea on how to fix this?
Does anyone else have this same model? Does it have the same 'problem'?

[Offroader Member Find all posts View Profile Close Offroader]

This doesn't sound normal.
Unfortunately troubleshooting and diagnostics are becoming a lost art in the workshop today. Unless the Toyota guys can plug in a computer and pull a fault code, then the problem doesn't exist. This is simply rubbish. I've seen faults go undetected by Toyota which will literally stop a car. Get a second opinion. SOme initial thoughts are:

- Bad ECM.
- Vacuum leak.
- Faulty throttle position sensor.

Let us know how you go.

[Jon Avid PP Poster! Find all posts View Profile Close Jon]

You are right with the fault codes...

The throttle body, throttle position sensor and the MAF sensor have been replaced, they only replaced the MAF after I showed them that it was out of spec.

What is the ECM?

I do feel it should not be up to me to find the fault with this vehicle that Toyota say does not exist, as they have no fault code!!!
This vehicle is still under warranty, quite a poor performance from Toyota. Need to rattle their cage I think ( have had to do this before with a 90 series).

[Offroader Member Find all posts View Profile Close Offroader]

The following is a troubleshooting guide for idle speed issues on the V6 Prado (Ellery's). Sometimes you need to encourage the mechanics to check them as they won't always take the initiative.

* Check Accelerator Linkage for sticking
* Check diagnostic/fault codes and output of diagnostic codes
* Check ISC system, Wiring connections, ISC valve, A/C switch
* Check TPS ( You've already had this done)
* Check fuel pressure
* Check fuel injectors for leakage and quality
* Check EFI Electronic Circuit: Wiring Power to ECU/ECM, relay, Air flow meter, Water temp sensor, Air temp sensor, injection signal circuit, injector wiring and ECU/ECM. ( ECU/ECM is the computer which interprets all the data from the car's sensors and then makes inputs to keep the engine running correctly. If this isn't working properly you may experience operational issues.

Seeing as your Prado is still under warranty, Toyota are obligated to sort the problem out. Sometimes it is worth trying another dealer as they may be more forthcoming in a diagnosis and fix.

[Darren D1 Lurker Find all posts View Profile Close Darren D1]

Jon,
Did you resolve the problem? What was the solution?
I've got exactly the same symptoms on my 2004 GX 4.0 V6 Petrol manual.
D.

[Liftman Lurker Find all posts View Profile Close Liftman]

Have the same problem

Darren D1 - when did you notice the problem?

[Darren D1 Lurker Find all posts View Profile Close Darren D1]

About 12 months ago I had the heads rebuilt on my '04 GX 4.0 V6 Petrol Prado (thanks to an inattentive apprentice leaving the radiator cap loose) and ever since the engine idles at 1200-1500rpm in the peak hour crawl. As soon as the car stops moving, idle returns to 800-900rpm. Costing about $300/qtr in poor fuel consumption.

The mechanic that did the head repair has checked MAF, Throttle body, EFI fault codes = nothing.

Took it back to Toyota. Same thing. Diagnostics (computer) shows no fault codes, but they can see the idle issue when the car is moving and it disappears when movement stops. Clueless.

Some threads talk about O2 sensors, others about coolant sensors, others about vacuum hoses. The sensors are expensive "trial & error" solutions. Just wondering whether anyone has found a resolution? Aside from irish minesweeping or selling the vehicle

[Jon Avid PP Poster! Find all posts View Profile Close Jon]

I feel like selling the vehicle....
If a new buyer asks about the idle, I would say that Toyota has stated that there is no fault code, therefore no problem...

[Steve M Addicted PP Member Find all posts View Profile Close Steve M]

http://www.mr4x4.com.au/index.php/co...dle-petrol-120 may help ??? Cheers Steve

[Steve M Addicted PP Member Find all posts View Profile Close Steve M]

http://www.toyota120.com/forum/showthread.php?t=22992

[Darren D1 Lurker Find all posts View Profile Close Darren D1]

ECU reset many times. TCB cleaned too. Still no fix.
Taking back to Toyo today to see if their $350 diagnosis comes up with anything better than "the computer says nothing is wrong".

[Bear63 Senior Member Find all posts View Profile Close Bear63]

has anybody thrown a scope on the electrics to make sure there are no voltage spikes,dirty feeds from the tps,maf etc?(this won't show up on a system diagnosis)

[Jon Avid PP Poster! Find all posts View Profile Close Jon]

It seems the MAF sensor does both functions of air flow and air temperature.
After the MAF sensor change last summer, the problem went away, however this only lasted until the air temperature dropped, then back to the original fault.
Something seems to have been disturbed or disconnected after work on the engine.
As there are so many inputs to the ECU, it seems that one input is out of specification, causing the problem.
What we need is a way to identify and check all of these inputs without costing a fortune.
I was thinking that the vehicle needs to be put on a dyno and have it running over 50 KMH with a diagnostic tool fitted to determine why the throttle does not close with no throttle input.

[Bear63 Senior Member Find all posts View Profile Close Bear63]

That's what we use a scope for Jon, probably the second most used bit of gear after the g-scan

[Jon Avid PP Poster! Find all posts View Profile Close Jon]

Pity Toyota don't know what that is or how to use it...

Anyway, I don't have a 'scope as I would not use it much.
I was thinking about the fact that the problem occurred after work was done in the engine bay, in my case fitting a dual battery system and a snorkel.
So, after using K.T. principals, I checked on what was changed when I fitted the battery system & had the snorkel fitted.
I determined that the earth connection from the MAF sensor and other sensors was changed to a different point. Checked the resistance from the new earth point to the battery found a resistance measurement of 7.5 ohms from the terminal to the battery negative. I cleaned the terminal and bolt, resistance changed to 5.5 ohms. Traced the resistance and found the crimped wire that connects the battery to the chassis had a resistance of 5.5 ohms.When driving home, noticed a marked improvement in the idle speed, although it was 32 degrees (last summer, problem disappeared) Tonight, I fitted an additional wire from the battery terminal to the chassis earth point. I will report on results tomorrow.