P38 2.5 diesel inlet manifold black gunge & poor idle when hot

Hi,
My first post after 65,000miles of trouble free driving! I have a few queries:

When hot my Manual P38 diesel starts idling like a pig when coming up to junctions, in town stop start driving etc.
A quick blip on the throttle fixes it (feels like a cylinder is not firing )

I decided to investigate the inlet manifold , EGR sensor and possibly the injectors.

When I took of the inlet manifold it was full of black gunge. I suspect a leaking turbo--any other theories as to the source of the "gunge"--is this normal--does not feel like it shold be so dirty. I suspect that oil to the turbo is leaking into the intercooler and on into the air intake.

I cleaned it all up, including the alloy inlet's to the valves. It ran much better, but still when hot it idles roughly (chugging away-a nightmare in town)-a blip on the throttle fixes it.

Car runs fine, does about 25mpg, and pulls well in all gears.

Second question-where can you get the tool to remove the injectors?

My last question concerns the turbo oil return. The metal oil pipe from the turbo feeds into the sump via a small rubber hose to make th 90deg turn, held by 2 jubille clips--is this normal? It continually leaks(drips), and often needs a new rubber hose and clips. Seems a strage design. One thoght is that the crankcase pressure is to high, causing it to blow loose.

Thanks for any advice.

Is it soot in the manifold? EGR valves have a tendany to allow a clog of soot to build up on the manifold, block it.

I've often been surprised at how much gunk builds up in the inlet. I asked my local garage about it a while ago - they said it was completely normal and doesn't do any harm.

Could be your EGR valve not opening / closing properly. Try closing it off and seeing if it makes any difference. Personally I wouldn't remove it permanently, but blanking if off temporarily will allow you to see if it is dead or not.

One thoght is that the crankcase pressure is to high, causing it to blow loose.

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Have you checked that the breather isn't blocked?

Matt.

Thanks for those replies.

The soot is oily (wet) and black.

The EGR unit appears to be functioning.

Still cant eradicate the poor idle when hot.

I'll block the EGR temporarily as its an emmission thing by removing and plugging the vacum hose that operates it.

Where is the breather? I spend a lot of my time looking for mystey parts on my P38, and thats with a workshop manual!

Hi,

Mr P38 DSE developed exactly the same problem at exactly the same milage - I still haven't cured it. Have you had any luck yet?

Bruce

Farkit said:

Hi,

Mr P38 DSE developed exactly the same problem at exactly the same milage - I still haven't cured it. Have you had any luck yet?

Bruce

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My 97 P38 DT with 96,000 has the same problem. Has anyone got any idea what could be causing this ?

Don

Same syptoms! Misfiring and erratic idle when stopping at juntions etc with ahot engine. Quick blip on the throttle cures it. I have replaced diesel return lines, fuel filter, engine coolant sensor (both of them). Still the same problem but each time I do work it seems to go away and then returns within a couple of days. My next job is to check the crankshaft position sensot that give both engine speed and position - problem is that youneed a Land Rover tool to set the distance correctly. If anyone finds a solution to this problem I really need to know. Could it be an ECU fault? No fault codes seem to have been logged. Richard

check fuel filter seal?
also it may sound stupid but if your garage that you get diesel from has old tanks then you may be buying water with your diesel.
water or air in system would cause an erratic idle.

good luck

I have just been told there is a low pressure electfic pump in the fuel tank that causes this problem when it fails. I haven't checked it out yet. Fuel filter seal is o.k. and no water in fuel. RB

If you have gunk in your inlet manifold you can bet you have the same in your intercooler, give it a good clear out with some petrol..... probably not causing your problem but the intercooler is often overlooked at service time and it makes abig difference to good runnind / efficency.

I have checked the 'in tank' electric fuel pump and the delivery is perfect at over the specified 180 ml per 10 seconds. Also today, I had a Bosch KT650 look at the ECU, codes and sensors and it found no error codes and nothing wrong with any sensors. First 7-10 miles is no problem but after that if you stop at a halt sign and go into neutral it starts chugging - slight blip on the throttle and it behaves properly. It's not water in the fuel and its not gunge in the intercooler or manifold and I also changed the four small O-rings on the fuel filter inlet & outlet the other day. This is starting to get annoying as it runs beautifully on the open road!

rrdiver said:

I have checked the 'in tank' electric fuel pump and the delivery is perfect at over the specified 180 ml per 10 seconds. Also today, I had a Bosch KT650 look at the ECU, codes and sensors and it found no error codes and nothing wrong with any sensors. First 7-10 miles is no problem but after that if you stop at a halt sign and go into neutral it starts chugging - slight blip on the throttle and it behaves properly. It's not water in the fuel and its not gunge in the intercooler or manifold and I also changed the four small O-rings on the fuel filter inlet & outlet the other day. This is starting to get annoying as it runs beautifully on the open road!

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Did you ever find a resolution to this problem? I have exactely the same problem (you desribe the symptoms perfectly) but mine is on a Vauxhall Omega fitted with the same 2.5TD BMW engine. Would love to get to the bottom of this.

Someone suggested to me that there is a potentiometer (for the drive-by-wire throttle system - not sure if the Range Rover is the same) on top of the diesel pump (I think removing the cover exposes this). Apparently this get's dirty and needs a clean up. Idle should return to normal once cleaned. Not sure if this is true though - I haven't had the bottle to take the cover off the pump incase I cause more problems and this piece of advice is a load of rubbish?

I don't know about the existance of a potentiometer on top of the tank fuel pump - if there is one i would think it would be to do with the fuel guage. What I did consider was that on the Range Rover the tank develops a partial vacuum as you use fuel and this is only partially released by a spring loaded non-return valve situated in the centre of the RR fuel tank filler cap. With the RR filler cap, if you turn it 180 degrees before opening it, it releases the vacuum from the tank. (This is all because of polution regulations not wanting to release fuel mist to the atmosphere.) Anyway, I figured that pumps are not efficient when pulling against a vacuum so I now leave the tank cap in the 'vacuum release' position permanently. The result is that my problem has gone away by about 98%. It only very occasionally does it now - most of the time it is perfect. This idicates to me that although the flow rate was o.k. from the in-tank pump on test, the possibility exists that it is either not developing enough pressure (worse in vacuum) or that perhaps deposits from the diesel fuel have reduced its efficiency on the inlet side, possibly by rendering a non-return valve 'leaky'. A different option if your cap does not have the 180 degree vent system would be to drill a small hole in a suitable place, but before doing all this, I would open the cap slowly ate the end of a long drive and see if it releases a vacuum? (You might hear it hiss!)