Lumpy Idle

[KiwipugUK]

I'm at a loss here, my HDi has developed a really lumpy idle. I've changed the injectors and all was well for about 1500 miles. Began to get noisy and lumpy so assumed one of the new injectors had failed. I was correct as a leak off test proved one was way off the others. Changed that one, but idle is still really lumpy. It runs beautifully when you're driving, loads of power and economy around 50mpg. When you come to a stop, within about 10 seconds the idle goes from smooth to lumpy, like so lumpy the hear rests are shaking. Any input from the accelerator makes it disappear, even 100rpm more than idle. Also if I have my foot on the brake and let the clutch out until it's just biting, again just enough to change the revs, it goes away too.
I really don't want to scrap the car as I've sunk a bit of cash into it to bring it up to standard after the previous owner neglected it, but there are some other issues (brakes&ball joints) that need attending to and combined with an engine issue it could be fatal!

[PeterN]

Its very unusual for these to have injector problems but it could be that there something in the fuel system that is causing them to stick. Have a look in your fuel filter and check it for brass filings, on the early engines the in tank pump used to fail and deposit bits of metal into the system, these could work their way through to then injectors.

Alternatively it could be that the compression is low on one cylinder due to bore wear or valve leakage. Its obviously missing on one cylinder and a faulty injector or low compression are the only possible reason I can think of.

I have three of these cars, two in use and one for spares, two have done over 200k miles and as far as I know still have the original injectors.

I would do another leak off test and check that you don't have another faulty injector, I take it these were secondhand injectors.

Peter

[KiwipugUK]

They were new recon ones, but yeah, should be fine! The are quite noisy tho, like a claking sound at low revs, so that makes me suspect them still. It could be compression, but wouldnt you be down on power or economy? I haven't check it tho, so can't rule it out. The engine has done 210k miles so I guess it could be knackered, but you're right, normally these 2.0l HDis go for ever and a day!

[frog]

I had the same issues a few months ago. I went through all electrical connectors that i could find under the bonnet, uplugged then and sprayed electrical contact spray on them. Reseat and release a couple of times, then release to let them dry for about 15 minutes before plugging all back in again. Also done this with the ECU, there are three rather large connectors going into it.

It improved the idle running remarkably, it is completely smooth now where it used to be somewhat irregular at times.

Make sure you visibly mark all the connectors that you take apart, e.g. by putting a colorful clothes peg on them. This to prevent you from forgetting to plug one or two back in.

[KiwipugUK]

Ok, so I tried the unplug everything and plug it back in scenario. I used a whole can of electrical cleaner, and result! The lumpy idle instead of being all the time is sometimes. Still starts lumpy, and with a cloud of grey smoke, but clears and will idle nicely. Then then it wont... the engine has quietened down too, the claking that I thought was an injector seems to be pretty much gone too. Going to have another go with electrical cleaner, could it be something like a bad earth somewhere? or broken earth strap too? The car managed to loose a little clip in cap inside the passengers side inner wing splash guard. Im not sure how long it was gone, but it has made a bit of a mess with surface rust and corroded terminals on the left side under the battery and fuse box. There was a row of green relays in a separate box to the fuse box that were pretty bad, cleaned them all up but I'm not sure what they do, glow plug control maybe?
I thought I was the connection to the air flow sensor, but have run car with out sensor and it still does it.
Any more ideas?

[frog]

That's exactly my experience, it takes 1-2 weeks for the contact spray to do its work. Can't explain why. Had this with the Saxo, engine management light going on and Lexia software reading a fault code that indicated a wrong lambda sensor signal. Spraying the connector helped, the fault code came back 2 or 3 times then after 2 weeks it was gone. That was 2 years ago, never a problem since.

And indeed, earth points are really important. Surely a good idea to check all the straps, unscrew the ring terminal connectors and make all contact surfaces shiny clean with a piece of sand paper.

Note: when you disconnect the earth strap in front of the battery (just behind the headlight), the BSI box gets unpowered. It often does not like that: it may lose its memory for the key fob and other stuff. If you want to play it safe it is best to use a single jump start cable to keep it clamped to earth while you unscrew and clean up the terminal.

Not sure which green relays you mean but in any case it is a good idea to check if all 4 glow plugs function correctly. Check if they get power if you turn up the contact key to "engine running" position (but without starting the engine). You should see 12 V coming in and out as you turn the key from ACC position to engine running position and back. If that is fine, then remove the plugs one by one and use a set of jump start cables to connect them directly to the battery. They should start glowing visibly after a few seconds. Be careful not to touch the glow plug, it will be hot. Also beware not to cause an electrical short ciruit!

The air flow sensor can indeed be disconnected. The engine management system will switch to using the air pressure sensor (located at the top of the intercooler). The engine will keep on running fine. If it suddenly and consequently runs a lot better when disconnected, then indeed the air flow sensor might be the culprit.