My car has started “jerking” when going on and off the throttle – ie if I clutch in at low revs in 1st then accelerate I get a big jerk as it revs up. I get a similar problem when changing gear – if I lift off when changing up (as normal practice) I then get a jerk when putting my foot on the accelerator again – the only way to avoid this is to spool the engine up and slip the clutch on each gear change. Also a jerk when lifting off – if I lift off the accelerator and then touch the accelerator again I get two “jerks”!

It’s a turbo diesel, so wondering if it’s something to do with the turbo – power and economy seems OK otherwise though. Is also getting on a bit – almost 150k miles and not worth a lot, hence reluctant to spend much on it (if the estimate to fix is >£500 I’ll be putting up with the problem until I scrap it, so no point in even paying to get it diagnosed in that case).

Thanks for any help.

Could be a bad injector pump or faulty most likely.

Vacuum relay failing is common at higher speed 50+mph wen the torque converter goes on/off.

Needs a pro diagnosis but at least your turbo is ok 🙂

It *could* be your vacuum hose burst or off. That’d cost about a quid to fix. Easily discovered. Lift the bonnet and rev the car with your ear near the engine. If you can hear a loud hissing/pumping noie, track it down.

Thanks – doesn’t sound like it’s as bad as I thought – I’ll have a look.

I’ll put £1 on it being the MAP sensor, I’m that confident. 😛

Nothing to do with Vacuum….. Diesels don’t produce Vacuum, so need a separate pump to produce it!!

Could be an EGR related fault, i.e. the car is EGR (ing) when it shouldn’t be, it should only EGR when on overrun or during cruise speeds

Knackered engine mount likely to cause this? Did as suggested above and watched as mrs aracer started and revved the engine, and it’s wiggling about all over the place – feeling underneath there seems to be a bit of rubber missing around a bolt.

Had wondered about engine mount in the first place given other symptoms I’ve been getting (vibration / noise which sounds a bit but not quite like a blowing exhaust), but didn’t think that would result in these symptoms – what does the STW car collective reckon?

Mine did that when the EGR was toast. I also had an old SAAB that was a bit wonky until I cleaned the MAF sensor. Easy peasy with a tin of squirty stuff. EGR was replaced for £££’s though 🙁

My first thought was a knackered engine or gearbox mount. What car is it ?

My first thought was a knackered engine or gearbox mount.

Thanks for the confirmation – a second opinion would also be good 😉 The obviously dodgy one I’ve found is a lower mount I think I can DIY, so nice and cheap and worth doing – though I need to have a proper look at all the mounts I guess. Car is a 12yo 406 estate with 150k miles, so worth very little, and I do plan to upgrade soon anyway, so really not worth spending much on it (if it weren’t for being unemployed I’d be looking at new ones right now – as it is I got a good redundancy payoff, have enough in my new car savings account to pay for a new one and fairly confident I can get another job when I start looking properly, but it makes me a bit nervous spending lots of money when I have no income!)

Could be the dual mass flywheel part of the clutch going knackered if it is doing it under drive or as mentioned earlier egr valve or an injector going down.

What make of car and size of engine is it ?

*edit* just seen you mention the type of car if the last post sorry 🙂

engine mount was my first guess.

Fuel filter, bad injector (usually shows excess smoke), EGR car usually struggles to pick up as the exhaust strangles the engine until the turbo forces enough air through and when it does you’ll be leaving a big cloud of smoke.
Without knowing the service history or make it could be many other factors like worn belt pulleys creating slackness and vibrations at low engine speeds that can create a judder through the engine.
DMF problems are usually accompanied with vibration, excess noise and starter motor squeal too.
Poor servicing and I would bet on fuel filter need replacing which on diesels is every 3 years at maximum but closer to every 2 years.

2nd on the engine mount.

could it be a windscreen wiper?

Thanks all – several confirmations that a knackered engine mount could result in these symptoms and the fact I’ve got one confirms what I’ll be doing on Monday. I’m assuming the lump of rubber will be fairly cheap, and it looks DIYable.

Buy a tube of silicon sealant and gun it into all the gaps on the mounts .
Leave it a few hours to go off then test drive . Should feel a whole load tighter up front .
Worked on a 200bhp Saab , so a Td 406 should be the same .

Buy a tube of silicon sealant and gun it into all the gaps on the mounts .

The trouble is, having got it off it appears it’s all gap and no bush! No wonder I’ve been having problems. The bracket the bush presses into is also a driveshaft support, so the official line is that I have to remove the driveshaft, making it a real arse of a job. I shall see if I can do it in place the standard bodger’s way with careful use of a freezer, grease and studding and big washers as a press. Wish me luck!

Wait until he’s right up behind you then put the brakes on hard. Smurfhat told me.