Hello,

I am getting very close to my rags end with the hunting / struggling idle problem on my 200tdi. I have gone through absolutely everything that I can. New fuel lines, new injectors, new injection pump, timing belt - EVERYTHING! The engine performs perfectly - plenty of power, will do 85mph BUT, the bugger will not idle properly.

I have adjusted the engine idle up on my injection pump, which works very well once the engine has warmed up etc, but from any initital start, the idle remains relatively standard, and only increases upto the new level if I blip the throttle. Sometimes, it maintains an idle that is as sweet as a nut, sometimes it drops back down and starts bobbling around randomly, or starts to hunt on one cylinder.

I have also noticed today, that it sometimes feels as if my 90 is bunny hopping / crabbing a little when coasting along in gear.

There does not seem to be any air in the system and there is plenty of fuel from the return line at the back of the pump. The lift pump is in good working order (it's brand new) and all filters and pipes are new.

Any ideas?
Thanks

-Tom

My first thing would be to check for an air leak in your inlet manifold gasket/ inlet pipes. Let it idle and spray the gasket in wd40 or something and see if the revs change??

That wont make any difference on a diesel.
Its got to be either fuel or timing related.


Lynall

Karlos28 said:

My first thing would be to check for an air leak in your inlet manifold gasket/ inlet pipes. Let it idle and spray the gasket in wd40 or something and see if the revs change??

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Snigger no spark plugs.

try dose of fuel injection cleaner, we have a van that doesn't like motorways- cold start in pump stops working dose of cleaner and it springs into life.

You may have a broken ring whch moves around on the piston or a worn valve guide or weak valve spring that does not always seat the valve as well as it could.

Just some suggestions to consider.

Thanks for all the replies.

The intake / exhaust manifold gasket isn't blowing between one another, so I can rule that out. The fuel supply is good and pure, with no air, and plenty being returned to the tank at both engine idle and at higher RPM's. The timing has also been triple checked, so that's all spot on.

As for Shifty's suggestions, they are all good things to consider. I can't imagine it being a broken ring, because that would show up as a few different problems, such as scoring of the cylinder walls and perhaps excessive crank case pressure, both of which are non-existant. A goofy valve spring is a possibility. What would a worn valve guide do and how do I fix it?

The problem is so intermittent. Sometimes it replicates its self multiple times during a run, sometimes it does not happen at all. Surely, if it were anything other than injection pump / injector related, it would crop up all the time, every time without fail?

Thanks again,
-Tom

Most valves turn in their guides as they operate due to harmonics at particular engine speeds. This is a good trait as it evens out the wear on the seat and valve. A worn valve guide can let the valve wobble and not always seat properly. Only way to fix it is to have new valve guides pressed into the head or to ream the guides and fit valves with oversize stems but this is a PITA assuming you could get the bits for your engine.

Whichever way you decided to go the valve seats would then have to be re-cut so that the valves run true to the new guides. Any decent cylinder head refurb place will be able to do this sort of work. Its not something you can do properly with a black and decker in your shed.

Of course it may not be the problem but if you've done everything else there's not much left to fix.

Shifty1962 said:

Most valves turn in their guides as they operate due to harmonics at particular engine speeds. This is a good trait as it evens out the wear on the seat and valve. A worn valve guide can let the valve wobble and not always seat properly. Only way to fix it is to have new valve guides pressed into the head or to ream the guides and fit valves with oversize stems but this is a PITA assuming you could get the bits for your engine.

Whichever way you decided to go the valve seats would then have to be re-cut so that the valves run true to the new guides. Any decent cylinder head refurb place will be able to do this sort of work. Its not something you can do properly with a black and decker in your shed.

Of course it may not be the problem but if you've done everything else there's not much left to fix.

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Cheers Shifty,

I suppose if the valve guides were worn, or the valve seats were coked up I would have a misfire on however many of the cylinders have valves in bad shape. It's just one of those things where I start to think, do I pour any more money into it or not. I've had a new pump, rebuilt my injectors and replaced the entire fuel supply system at a few hundred quid in total - which would have bought me another tdi! That said, I would only end up running into similar problems in future.

I do know a good local firm who collect, cut and then return cylinder heads / blocks the same working day and they are reasonably priced too. I have a few more things that I want to try out first - the head was only skimmed last year, I should have let them do the valves and the lot! I might even take my injection pump / injectors to a different diesel shop to get them tested and see how they come back. It still strikes me as being an air in the fuel problem, but there really doesn't appear to be any I am fairly certain that it is just ONE cylinder that is causing the problem, because when it decides that it is going to start hunting, it only does it on one cylinder, not two or more. Slackening the injector pipes on each cylinder in turn gives the same results to the engine though, so it's not like I've got a dead injector.

I am still half thinking along the lines of stripping my timing gear off to check for any play / damage to the cam shaft and crank keys / key ways. I don't suppose it would be impossible for a tensioner / idler pulley to have a problem, or the belt to be a little slack etc. Although, I have been in there twice to check the timing.

It's just one of those ball ache things! If I had all the necessary tools and a bit of cover at home, I'd be on with it like a shot.

-Tom

If it was the valve seats it would be a problem all the time.

If the engine runs good most of the time cant you live with it until funds/time allows? No engine runs spot on steady idle all the time. Even fancy electronic controlled ones.

Hi, i take it all the parts have been replaced to try and cure this problem ? I dont think any worn internal parts could cause hunting.. It has to be fuel or air.. is it the same fuel in the tank ( Contaminated ) ? Does it smoke when it hunt ?

Shifty1962 said:

If it was the valve seats it would be a problem all the time.

If the engine runs good most of the time cant you live with it until funds/time allows? No engine runs spot on steady idle all the time. Even fancy electronic controlled ones.

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That's kind of what I had thought. The engine doesn't always run well, hence my frustration, but it is something that I can live with if I have to. I have just been taking a good look at the new injection pump. It certainly is a Land Rover component, all the part numbers match up etc. BUT, I do have a feeling that the throttle arm may not have been indexed to the throttle spindle correctly. The position of the throttle spindle in conjunction with the throttle arm determines the initial position of the governor. At idle, if the governor is reducing fuel to the engine to the extent that it hunts or simply can not maintain an idle, it may be that I need to rotate the spindle anti-clockwise one or two splines to adjust the fuel governing at idle. I will mark everything up and give it a try over the weekend. If it doesn't improve anything, I will adjust it back and look for other problems!

-Tom

steve-c said:

Hi, i take it all the parts have been replaced to try and cure this problem ? I dont think any worn internal parts could cause hunting.. It has to be fuel or air.. is it the same fuel in the tank ( Contaminated ) ? Does it smoke when it hunt ?

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Hi,

Yes each and every part in the fuel delivery / injection side of the engine has been replaced. From the pickup pipe in the tank, through the fuel lines, the lift pump, fuel filter head, injection pump, injector pipes, injectors, spill rail and return line! I am stripping everything back out at present, ready to put it all back together to make entirely sure that there are no air leaks in the system.

The fuel tank has not been completely drained, but I have probably been through about fifteen full tanks of diesel since the problem first started, maybe more.

-Tom