Jerky acceleration...

Fri Feb 22, 2008 10:20 pm

Went to look at a Cabrio today. Only major niggle was the engine. LOL!

It seemed smooth and strong (318i M40) but the gas pedal seemed a little stiff.

The main issue was whenever I put my foot down or lifted off the throttle the car would lurch. Was tough to get a smooth gear-change because of this, though the gearbox felt fine.

Any ideas? I thought worn engine mounts/gearbox mounts?

Fri Feb 22, 2008 10:50 pm

Oh yeah, it was worse at low speed.

Fri Feb 22, 2008 11:10 pm

Engine fault or drivetrain fault? Either way, I wouldn't worry to much about it - just use it to drive the price down!
Whatever it is, we can fix it on here at little expense. Ordinary M40 bits are of little value.

Sat Feb 23, 2008 8:41 am

Done a bit of research and it could be Diff backlash, engine mounts or Vac/Breathing system?
I don't want to go near it if it's a going to be anything more than a quick and easy fix...

Sat Feb 23, 2008 11:33 pm

Any more ideas?

Car is still available...

I've talked to a few more 'mechanics' who have said could be faulty ECU cutting power off too early when you lift off the throttle.
Also could be diff mounts.

But they ain't E30 bods...

Can't be control arms / bushes as they all felt solid taking hits.

Sat Feb 23, 2008 11:53 pm

I've replaced my diff, diff bush, centre bearing on the prop, inlet manifold gasket, afm, checked throttle body/switch, breathers, mounts etc. and still haven't found the cause of my kangarooing so tbh honest whilst I'd still say its probably an easy fix you have plenty of bargaining power on this issue. (my engine is m42 though)

Sun Feb 24, 2008 9:18 am

I'll leave it then.

Doesn't that drive you mental tho?

You might also like to try engine and gearbox mounts - apparently these make a huge difference and are cheap and easy.
Try and borrow a working ECU and try that too.

Sun Feb 24, 2008 11:37 am

Yes I'm going mad -I'll get it in the end. Think I've done everything on the air/fuel side, forgot to mention new fuel rail, pressure regulator, fuel lines. Might try coils and leads and ecu now. But back to topic I wouldn't write off that cab if the body is good like Brian said M40 bits are cheap and bodywork isn't.

Sun Feb 24, 2008 11:46 am

Yeh but I only want one to enjoy the alleged mental summer we're going to have.

I don't want a project or any work - just something to coast around in for a few months and there's nothing close for what you get money wise.

And this thing cannot coast!

I'm almost certain it feels like a bush or mount problem just because of the violence of the lurching when lifting off the throttle.

Post up any new info you find - it's useful in any case...

Sun Mar 09, 2008 1:42 pm

anisotropy wrote:Yes I'm going mad -I'll get it in the end. Think I've done everything on the air/fuel side, forgot to mention new fuel rail, pressure regulator, fuel lines. Might try coils and leads and ecu now. But back to topic I wouldn't write off that cab if the body is good like Brian said M40 bits are cheap and bodywork isn't.

This could very easily be a stiff or sticky throttle cable.

You press the gas, the cable goes nowhere but when it does move it goes to far as you've lept pressing to get it do something. Results in lungey acceleration and also the same in reverse via engine braking.

try a new able first, only about Ã‚£15 as it's a cheap fix if it works before you go spending more on major stuff.