Intermittent Acceleration D4d

Boian

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I am in bulgaria
Sep 8, 2017
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Help!

An year ago there was something like intermittent acceleration on my 2001 D4d automatic Prado and the fix was SCVs. However this issue appeared again. I changed the SCVs again just in case, but its still the same.

The acceleration hesitation and delay are most prominent when the car is hot and under the sun, like something is heavily choking her. Just getting in the shade and the acceleration improves a bit. But its like every time I hit the gas pedal the acceleration and the delay are a bit different!? Car pulls like train when cold.

- SCVs replaced
- MAF replaced with Denso
- MAP cleaned /although not sure if that totally true, you can not inspect it/
- Injectors were serviced by the official Toyota dealer
- Fuel filter replaced
- Batteries disconnected once
- Air temperature sensor cleaned /it wasn't really bad, but it could be dead anyway, might just replace it/

Any other ideas? What can be related to not accelerating when the car is hot?
- Catalytic Converter?
- O2 Sensor?
- EGR? I think it should be running slow no matter if it is hot or cold
- Throttle body?
- Manifold pressure sensor?
- Spark plugs?

Thanks!
 
Last edited:

Bob

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Any chance it could be autobox related? Other than SCVs, there's not much on these engines that gives any trouble.
 

StarCruiser

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This sounds a little like a poor connection to me. Does it show any codes if a dealer level scan tool is plugged in?
 

Boian

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Sep 8, 2017
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No codes. I just cleaned the egr and replaced the spark plugs, the problem is still here. It again happens when the cars is warm and i.e. stayed under the sun.
 
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Shayne

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I recall someone having issues with the digitally controlled turbo but memory is vague , stepper motor maybe ?
 

StarCruiser

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If it’s a D4D it’s a diesel so has no spark plugs. I guess you’ve changed the heater plugs which only assist starting and emissions control.

I think Higgy had a turbo actuator problem where there was a poor connection at the connector to the turbo.

You really need to prove a part faulty before replacing it otherwise you’re just throwing good money after bad.

Have a check of the turbo connector. Look for any corrosion, carefully inspect the wires for any bulges, nicks or cuts that could indicate breaks. See if wiggling the connector makes the turbo work or not.
 

Boian

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Sep 8, 2017
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Thanks, StarCruiser, yes I replaced the glow plugs, there are no spark plugs in this engine. I'll check the cable tomorrow.

Meanwhile there were some suggestions it could be the Throttle Position Sensor or the Acceleration Pedal Position Sensor. Could these be influenced so much by the rising daily temperatures here /~30 C/? The price for the combo was $1000 and I really don't want to invest blindly, I can't return the parts back if the problem doesn't solve... Could it be also fault in the motor opening the Throttle?
 

StarCruiser

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The answer is yes there could be any fault with any electrical part. I would expect the throttle position sensor (aka Accellerator position sensor, aka electronic throttle pedal) to give more intermittent operation all the time and be less susceptible to outside temperature. I think we can rule this out. As it’s a Diesel engine I wouldn’t expect it to have a motorised throttle or butterfly valve. The modern electronic diesels have a butterfly in the air intake to help shut down the engine cleanly, they aren’t like those in a petrol (gasoline) engine where they directly control the fuel air mixture entering the cylinders in order to regulate engine power and speed so I doubt it is this. These butterfly valves are often either open or closed and are sometimes worked by a vacuum actuator and solenoid valve.
Why do I not think it’s the pedal? You have no codes, they are basic devices present in many control systems and don’t often go wrong. It’s not impossible, but I would say it’s low on the list. Let’s face it, if it’s hot outside, you’ll have the AC on, so temp in the car will be reasonably constant.
Why the turbo? It’s in a hot area, I believe it is a variable vane unit on the D4D (do remember here my info is limited on this engine) which is varied by the ECU. It is not unheard of for ECUs to have faults. I think it would be less temperature sensitive as the ECU is sealed in a case.
I would check all wiring connections for corrosion and broken seals/wires.
 
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Boian

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I am in bulgaria
Sep 8, 2017
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Still haven't figured out the problem. Things around the turbo seem to be fine.

Now that it is a bit colder here the problem seems to appear less frequently, but I have a new observation.
When turning on the AC the issue appears almost immediately, turning it off it goes away in a couple of minutes.
Jeez, could there be any sensor that is influenced that bad by the AC?

Last time when I parked with the AC on and started the car again I kicked the gas pedal and stayed in one place for 6-8 seconds before I felt any acceleration and engine revving. Turned the AC Off - voilas, car was running fine.
 

Finiterex

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Far as I know engaging ac will increase the revs slightly on d4ds, its electronically controlled. My guess would be a sticky throttle actuator.
 

StarCruiser

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Have you checked intake ducting for leaks? My current thought is that outside temperature is not being followed by the ECU but the warm air (from the AC condenser) is being sucked in beyond the temperature sensor.
 

Boian

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Sep 8, 2017
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Thank you for the suggestions, I'll take a look and write back if anything new.
 
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