150 Tid tickover

[Alan]

My 2007 150 Tid ( 65,000 miles ) has started shaking when the engine it ticking over. Initially it only did it once or twice a month with a hot engine but not long after having a new alternator fitted it started doing it more or less all the time hot or cold.
If I touch the throttle to bring the revs up there is a slight hesitation that feels like a misfire but as soon as the revs start to rise above tickover there is no sign of it.
I've read on here that when the DMF starts to go you get a noise from it and mine has no extra noises so could it be the No 3 injector wiring I've read about ( disturbed when the alternator was fitted ). Or something else ?

       Thanks  Alan

[Petemate]

Hi Alan. Having replaced the alternator on my 150, I know that there should not be any reason to go near the injector wiring, as the alternator is removed from the top rear of the engine. Others will probably advise you to wriggle the No. 3 injector while the engine is running to see if this makes any difference - the dubiously good thing with your car is that the symptom is showing rather than intermittent, which is the worst type of fault to find. I personally do not think that a failing/blocking DMF would show as a poor idle. However, do you give the car a good 'thrash' occasionally? Like a run at over 2000 RPM for 15-30 mins or so?
Good luck
Pete

[Audax]

I personally do not think that a failing/blocking DMF would show as a poor idle.

I'm afraid that a failing DMF can and does show as a poor idle, I've seen them put the check engine light on too because of this. Other than that, yes, fiddling with injector number 3 wiring is the sensible way forward. There is also a software update to improve the idle of some cars, it might be that this car needs that update.

[Petemate]

OOoops - thanks Audax, I bow to your experience and will watch out for that especially with my replacement car, not knowing how it has been used.
Pete

[Alan]

It gets regular runs at 2000rpm + so I think the DPF can be ruled out if that's what you were thinking.
AA man fitted alternator and thought he might have caught the injector wiring when he was leaning over the engine and if it was starting to go he might have made it worse.
Been out in it earlier and the engine was shaking on tickover as bad as it ever has as soon as it started, stopped at traffic lights after a couple of miles and it was ticking over smooth but giving a bump as if it miss fired every 10 seconds or so. 
Couple more questions.
Is number 1 at cam belt end.
Would dealer do the software update as part of a service or only if the car had a tick over problem ( it has full main dealer service history )

[phoenix]

The alternator is used to govern idle control (it feeds s signal to the engine management to say how much load there is and make adjustment for it). I'm not sure but I think I've seen somewhere that there's a reset needed when a new alternator is fitted.

[Petemate]

The alternator is used to govern idle control (it feeds s signal to the engine management to say how much load there is and make adjustment for it). I'm not sure but I think I've seen somewhere that there's a reset needed when a new alternator is fitted.

You could well be on it there - when I fitted mine, after the old one went off duty, the thing wouldn't charge at first. I then did the disconnect and reconnect thing and away it went, no probs since. The disconnection, I was told, allegedly does a basic reset. AA man came out to my place of work a week or so after we bought the car when the key wouldn't do anything - he just disconnected the neg terminal and refitted it after a few minutes, mentioning something about resets.
HTH

[sgould]

Reset is listed in workshop manual, after fitting alternator, but it's listed as "after battery disconnection".

So, it's only the clock, calendar, ignition key and pinch protection. Not a Tech2 thing.

[Alan]

The check engine light was on after he'd fitted it. It came up on his computer as air flow meter ( or something like that ) and he thought it was because he'd disconnected it before disconnecting the battery.
I'll have a twiddle at the wiring tomorrow and see what happens.

                Alan

[Alan]

Ok finally found time to play.
Started it up from cold and pushed pulled twiddled with the wiring to injector 3.
Tickover stayed more or less the same all the time but it wasn't as bad as it had been, when I restarted it after putting the cover back tickover was a lot smoother, the bump as if it missed a beat has almost gone, it's still there on tickover but not as often and not as noticeable.
There are marks made by the injector wiring on the foam liner that fits under the cover so I'm 90% sure it's the No 3 wiring causing it.
I'll be passing within half a mile of the dealers next week so I'll call in for the repair kit.

Thanks to you all for taking the time to help.
                  Alan