Hi, I have a 2004 Mazda MPV, 2.0 diesel. The problem started yesterday morning. went to drive and no acceleration. pulled over and when you put your foot hard down on accelerator the reves only go up to 1500rpm. took to garage and the diagnostics came up with a faulty throttle potentiometer... So got one from scrapyard for £5 instead of £182 that Mazda wanted. fitted this and thought it was fixed as it reved. went to drive and same problem. now it will rev when first started but as soon as the reves drop below 2000 u loose the throttle again... so can pull over and do a flying start and keep reves up to drive. when you do this sometimes it will be fine even when the reves drop and drive like normal till you stop and turn off... then start again and problem back... I cant locate a throttle in the engine bay. so any ideas would be appreciated as this has me stumped at the moment... Thanks

 

That's an old diesel. Any issues with the dpf? Diesel Particulate Filter in the exhaust?

 

Blocked catalytic converter maybe?

 

Thanks but none of these!. i am managing to drive around by keeping the reves high for a minute or two from start up. After that u can drive normally and all works fine. So im guessing i might need to try another throttle potentiometer as the one i got as i mentioned was from the scrappy and of a different mazda model. It looks the same but maybe the resistance or something is different so the engine management doesn't like it.. Would much prefer a cable to drive by wire as Electronics is not my strong point. Still if anyone else has any theories please let me know as i would like to get to the bottom of this.

 

Now your talking! Especially since diagnostics support this.
Make sure you disconnect battery negative terminal, followed by a few brake applications, before installing it.

 

I have absolutely no practical experience with Diesels. I understand that they have no throttle. Instead of it they use the fuel to modulate the power output. I would first check the fuel filter and the fuel pump and injectors.

Also you should be able to find the specs for your throttle potentiometer and test it with a multimeter. Then please follow the electrical circuit and disconnect inspect/ clean and reconnect all harnesses and connectors. Make sure all ground connections are good.

Since this stuff is electronic even a wonky charging system and battery could throw it for a loop.

 

What I've highlighted in red seems to be cold idle related and not necessarily throttle.
So once the car is warmed up you don't have any issues?

 

Here is a diagram of a typical Diesel engine:

I am thinking any of the sensors and the solenoids could be part of the problem.

Here is the source: | Repair Guides | Diesel Emission Controls | Diesel Emission Controls | AutoZone.com

 

Once it's warmed up it seems to drive fine until i switch the engine off then it will play up again i have noticed on a couple of occasions that even with high revs it will suddenly "loose power" so to speak and go back to the safe idol of 1500 rpm which is annoying when i'm driving at 60 down a road and all of a sudden it will only do 42 mph in 5th gear

 

Thanks will try that