Strange throttle behaviour - 1KZ-TE

[crustyoldgx Lurker Find all posts View Profile Close crustyoldgx]

Hey Pointers, I am having a small problem with a '03 Prado GX 5 speed diesel. It is a recent acquisition for me, so I am still familiarising myself with the quirks.

What happens is the throttle seems to hang in the upper rev range when accelerating. When I take off in 1st, put foot on clutch and take foot off the accelerator to shift, the revs stay where they are at for a second or two before the engine slows down, almost like the ETC is holding the throttle open before closing the butterfly. It does this basically through all gears. Even if I just take my foot off the accelerator if I come upon a car going slower the engine powers on for a second or two before slowing down, which can be quite disconcerting! I suspect it may just be a sensor or something like that, but I'm not sure where to start looking. I have put a can of Threebond Diesel Conditioner through it as the throttle body looked a little junked up, but this hasn't made any noticeable difference.

Any ideas anyone?

Cheers, Chris.

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

how many kms has it done mate ? id guess alot being an 03 ?

I have an 04 1kz and just did a de grud of the throttle body and manifold, mine is getting close to the 300km mark and was filthy but still never performed like what you explaining. I guess it cant hurt to pull off the throttle body and give it good clean out.,it could be sticking

http://www.pradopoint.com/showthread...-throttle-body

check out the grud

[crustyoldgx Lurker Find all posts View Profile Close crustyoldgx]

Hey zutta, it's done 530 thou! I got it cheap (less than 8k) so I figured it was going to need some love. I might go the whole hog and pull the throttle body off. I pulled the radiator out last night cause it's been getting quite hot when driving on the freeway, and it's a write off. So I think I've got some work ahead of me to get it running just right. The block is going to need a really good flush out based on the color of the water that drained out of the radiator. And I still haven't ruled out a cracked head :-(. Are there instructions for pulling off the inlet manifold anywhere here on PP?

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

Also check for a damper on the butterfly, some cars have a damper to stop the throttle closing to quickly,
if it has one might also be the problem.

[adrian5800 Advanced Member Find all posts View Profile Close adrian5800]

It's not a throttle assembly, it's only purpose is to create vacuum for egr and to reduce harshness when the engine's shut down.
I have removed mine for a few reasons.
OP - 1kz's do have some delay when you come off the accelerator.

[Pradonut Lurker Find all posts View Profile Close Pradonut]

OK ,another theory. The computer gets a speed sense from your speedo pickup which holds the revs slightly to make for smoother gear changes. Try pulling the plug off on the gearbox and see what happens. You may only need to disconnect the battery for a while to clear a held fault.

[crustyoldgx Lurker Find all posts View Profile Close crustyoldgx]

Hey guys, some interesting responses. Adrian, are you saying you removed the butterfly altogether? Pradonut, I might just disconnect the battery for a while anyway and see if that helps. Leigh, how would I tell if there's a damper? I might also inspect and clean all of the vacuum lines attached around the throttle body.

Thanks for your ideas!

[adrian5800 Advanced Member Find all posts View Profile Close adrian5800]

Hey guys, some interesting responses. Adrian, are you saying you removed the butterfly altogether? Pradonut, I might just disconnect the battery for a while anyway and see if that helps. Leigh, how would I tell if there's a damper? I might also inspect and clean all of the vacuum lines attached around the throttle body.

Thanks for your ideas!

Yeah you can drill out the screws (with the housing removed from the engine of course) and remove the "throttle" plate altogether. My egr is blanked completely and I don't particularly care about the truck like shake as the engine stops. The added bonus of more air entering the intake is the engine starts now on less than one revolution of the crank.

The plate is controlled by a stepper motor via the ecu and doesn't function as a throttle, diesels aren't the same as petrol engines in the need to control the amount of air entering the cylinders. There is no damper on the plate other than the stepper motor.

I would use techstream and a cable and get someone to drive the vehicle and watch the accelerator sensor output.

[Idy10 Lurker Find all posts View Profile Close Idy10]

Hi guys from a uk prado owner
2005 6 speed manual that has the same problem , any one come with a fix yet?
Thanks

[crustyoldgx Lurker Find all posts View Profile Close crustyoldgx]

The plate is controlled by a stepper motor via the ecu and doesn't function as a throttle, diesels aren't the same as petrol engines in the need to control the amount of air entering the cylinders. There is no damper on the plate other than the stepper motor.

I remember my crusty old '78 BJ40 'Cruiser with the 3L 4 cyl diesel had a butterfly that controlled the engine speed! I know that these engines are a lot more advanced, but I wasn't sure whether the butterfly on this one had anything to do with engine speed or not.

I would use techstream and a cable and get someone to drive the vehicle and watch the accelerator sensor output.

Techstream? Is that software to plug in to the ECU? Where would I get a cable from?

[adrian5800 Advanced Member Find all posts View Profile Close adrian5800]

I remember my crusty old '78 BJ40 'Cruiser with the 3L 4 cyl diesel had a butterfly that controlled the engine speed! I know that these engines are a lot more advanced, but I wasn't sure whether the butterfly on this one had anything to do with engine speed or not.



Techstream? Is that software to plug in to the ECU? Where would I get a cable from?

Diesel engine speed is controlled by fuel injection amount, the air entering the engine is always in excess of what's required (hopefully) the butterfly your referring to is probably there to create vacuum and provide some engine braking effect.

Search on ebay for a cable and software for around $20 http://tinyurl.com/k57dswt

[znelbok Member Find all posts View Profile Close znelbok]

I have the same issue. As a new over of an '03 Prado I have noticed this a lot - more so in first and it is very annoying. Makes my 2.8L diesel Hilux feel like a sports car.

As for vacuum - doesn't the alternator have a vacuum pump on the back of it to create the vacuum required - does on my hilux so I assumed it was the same on all diesels (hence the dual belts for the alternator cause vacuum is a safety thing for the car).

[Pradonut Lurker Find all posts View Profile Close Pradonut]

Yes, they have a vacuum pump. The butterfly is to create a manifold vacuum at idle to draw the exhaust gases through the EGR. Why some on here have removed it once the EGR is disabled. Interesting, I had never made the connection of the easier start -mine too fires up in about half a revolution.

[Idy10 Lurker Find all posts View Profile Close Idy10]

hi
still no solution , is seems to be quite a common thing with quite a few Toyota models running the d4d engines and nobody can come up with a fix other that sell it , one last shout for a remedy!

[AussieAndy Find all posts View Profile Close AussieAndy]

I remember my crusty old '78 BJ40 'Cruiser with the 3L 4 cyl diesel had a butterfly that controlled the engine speed! I know that these engines are a lot more advanced, but I wasn't sure whether the butterfly on this one had anything to do with engine speed or not.



Techstream? Is that software to plug in to the ECU? Where would I get a cable from?

OT, but the butterfly on the bj40 actually did control engine speed in a sense. It uses a weird vacuum valve set up on the back of the fuel pump, it picks up the vaccum difference across the butterfly and uses that to control the amount of fuel delivered. By closing the throttle butterfly the vacuum difference was great so no fuel, open = no difference = full fuel. The diaphragm wears in these, gets a split in it and the engine idle rises.