Uneven running at around 1200 RPM

[t1pper]

Hi,
I have noticed that my 1999 100 diesel is not running smoothly at around 1200 rpm, I have changed the fuel filter but without improvement.

It sounds like it is hunting or pulsing when its on light throttle its more noticeable when pulling away from a standstill gently as the rpm's increase it smooths out or if you accelerate hard from a standstill it runs through the rev range cleanly.

It strikes me that it is more a sensor or throttle pedal position sensor fault, to date no warning lights are on and within the last 2 weeks I have covered around 2,00 miles without the problem developing.

Nearly 100% sure its not a fuel blockage type problem, any body got any ideas?

 

[StarCruiser]

Can't help but interested in this thread to see if there's any similarity to my 1HD-T vibration. Hope you find it.

 

[frank rabbets]

Might be oil/carbon deposit on what is known as the "throttle body" on the inlet side of the engine. As it is easy to take this off and clean it I would check. Also check any electrical connections are clean.

 

[t1pper]

Hi StarCruiser,
My engine is running very smooth its just a bit of uneven running at 1200rpm.

Thanks Frank, I will check that out!

It sounds like a good place to start, I removed the inlet pipe up to this the other day and it did look a bit grubby in there so I will have it out, give it a clean and report back.

 

[StarCruiser]

Ok, thanks t1p

 

[frank rabbets]

It's the body with the butterfly and spindle. If there is carbon the butterfly might be slightly open but the carbon restricts the airflow so the wrong amount of air passes through causing hunting. On fuller throttle all is OK. That is with petrol engines but I am guessing it might possibly affect diesel engines. Quite easy so worth a try.

 

[t1pper]

Well I cleaned out the butterfly and the small matrix in the inlet side of the engine it was a bit grubby but not too bad really, cleaned with brake cleaner and an airline.
Still have the uneven running during light load, I think I will have a close look at the throttle pedal and some of the vacuum lines and valves around the engine next.

 

[jbecks]

I was reading a thread the other day about similar issues, check your pedal for the accerlator position sensor and carefully remove the enclosure of the sensor, give the pcb and spindle a good clean whilst rotating the pedal. I can't find the thread now but I think it was on ih8mud.

 

[t1pper]

I was reading a thread the other day about similar issues, check your pedal for the accerlator position sensor and carefully remove the enclosure of the sensor, give the pcb and spindle a good clean whilst rotating the pedal. I can't find the thread now but I think it was on ih8mud.

Had the pedal out and cleand it up as you discribe with a good dose of electrical contact cleaner and dried it out with air line but it made no difference what so ever.
Not sure where to look now??