arabpj

1998 1 kz idle worry?diesel.

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Hi..After years of wonderful reliability my Regius developed strange habit.At random times idle increases to 1400 rev and runs like a petrol engine overchoked.After half a minute settles down to 700 perfect.Annoying and dangerous at intersection.can go for two weeks well behaved.Not high mileage.No fault code shows.I wish i could fix this.Other engine performance is great.Can anybody help me please..Paul..NZ.

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Moved to the Toyota MPV club.

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Process of elimination I guess.....has a competent diesel mechanic had a look.?

TBH I'd guess there are far more Regius's in your part of the world than there are here.!

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Thanks for replying.I took it to a business diesel pumps ltd but of course car didn't misbehave there and no fault code showed loaded.They were at a loss. I thought somebody may have had similar fault.It is a 1kz te engine same as Prado round same year so I suspect quite common beast.Its a pain..idle speed doubles and engine hunts and rocks vehicle from side to side.Then it will settle down and idle properly.I hope its not something I don't understand like an ecu if there is one.Very peculiar..No smoke no loss of power no hard starting no overheating.I am wondering whether a 1 kz manual would be of help to me if I can find one..Thanks anyway.

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I sympathise mate,...nothing worse than intermittent faults that don't give or leave any trace or record of what might be the cause.

There has to be a reason of course...but I guess you'd have a better chance of finding the culprit if the vehicle could be tested/checked WHEN the fault was actually present.?

Good luck with it...hope you find the gremlin.

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Thanks for your interest great.I am older qualified mechanic but not diesel.Looks like its a challenge.Maybe I could start by blocking off some air lines in case its an air leak.Like brake booster.Maybe fit clear hose and look for bubbles in fuel.i am wondering what actually controls idling in a diesel?Maybe the spill valve.Its obvious I haven't a clue.I can tell you its b  annoying at the traffic lights.Is it related to the automatic somehow or foot on the brakes.My head is going round and round.If it would just increase the idle smoothly might help.But the roughness/hunting type behaviour is scary.Thanks again.

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3 hours ago, arabpj said:

Thanks for your interest great.I am older qualified mechanic but not diesel.Looks like its a challenge.Maybe I could start by blocking off some air lines in case its an air leak.Like brake booster.Maybe fit clear hose and look for bubbles in fuel.i am wondering what actually controls idling in a diesel?Maybe the spill valve.Its obvious I haven't a clue.I can tell you its b  annoying at the traffic lights.Is it related to the automatic somehow or foot on the brakes.My head is going round and round.If it would just increase the idle smoothly might help.But the roughness/hunting type behaviour is scary.Thanks again.

I'd look towards injectors, especially when you mention the the roughness and hunting behavior.

Then check your mass air sensor, maybe it's dirty and doesn't read the incoming air correctly.

Also could be an issue with accelerator pedal sensor, if you have drive-by-wire. Do you know if you have a physical wire operating your accelerator or is it controlled by ECU?

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Thank you for ideas great.On examination I see this vehicle has a physical Bowden type cable connected  to the accelerator pedal this rotating what I presume butterfly type mechanism at the top of the engine near the tappet cover.I am wondering if the mass air sensor is the sensor in the air intake just after the air filter location?I pulled that out one day.Nothing for me to see just a plastic type sensor protruding into the air flow.Wire attached. Thanks.

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Yes, that's the MAF sensor, and since it's a tiny strip of wire, it can get contaminated over time. The only way to clean it is with a special MAF sensor cleaner, but you can also look into diagnostic methods, for example, trying to run the car with the sensor not powered on.

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w oll thanks that's pretty clever.I didn't notice any strip of wire just a black plastic prod looking thing about 30 mm.My latest thoughts are some sensor misbehaving which one I do not know.could well be this one.Its something that also increases the revs from the 700 to about double i.e.1400.I am shying away from injectors at moment because engine is pretty sound and has had a quiet life to 130,000kms.thanks great..some one to share thoughts with.

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Hi..I could not find a picture of a sensor like mine and I thought funny.Then I discovered the one on the 1kz te engine is called a air temperature sensor.Then I saw pictures like mine.I would guess they both do a similar task.I am just guessing but say this sensor controls diesel  quantity through a ECU..if faulty could affect idle through over supply which would sound like a petrol engine does when overchoked or running with rich mixture.Please don't laugh this is pure speculation.no knowledge involved here.

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