318 hunting on acceleration

Thread view:

Enable EMail Alerts

Start New Thread

Thread rating:

Tony - 13 Apr 2009 02:38 GMT

My friends 1997 318i coupe seems to be suffering badly on acceleration
in first gear only. It hunts severely unless the clutch is slipped, it
seems to step up the revs in 1000rpm steps as if you are jumping on and
off the accelerator at those points.

Other gears power seems to be normal, but I'm not sure how powerful this
should be.

It hasn't been all that well looked after, still has same spark plugs in
from when he bought it, but he would change them if he thought it would
help.

Feels more like an engine problem rather than clutch or drive related,
just too severe and on/off.

Any clues?

--
Tony

Reply to this Message

Scott Dorsey - 13 Apr 2009 03:48 GMT

>My friends 1997 318i coupe seems to be suffering badly on acceleration
>in first gear only. It hunts severely unless the clutch is slipped, it
>seems to step up the revs in 1000rpm steps as if you are jumping on and
>off the accelerator at those points.

>It hasn't been all that well looked after, still has same spark plugs in
>from when he bought it, but he would change them if he thought it would
>help.

How many miles does it have on it since he bought it? Does it have the
same fuel filter, air filter, and oil?

If it were me, I'd first do all the preventative maintenance on the
schedule that has been missed, then I'd do a general look over for
vacuum leaks, then I'd pull the codes off the computer and see what it's
saying. All kinds of things can cause this sort of behaviour, including
believe it or not, the oxygen sensor. But vacuum leaks are high on the
list.
--scott

Signature

"C'est un Nagra. C'est suisse, et tres, tres precis."

Reply to this Message

John Burns - 14 Apr 2009 11:55 GMT

I agree with Scott, good chance it's a vacuum leak. Most likely one is a
ripped hose from the throttle body to the air flow sensor (the biggest
hose in the enge bay), you'll likely need to flex it to reveal the rip.

If the car has no history you really need to fit new spark plugs and
change ALL the fluids and filters.

> How many miles does it have on it since he bought it? Does it have the
> same fuel filter, air filter, and oil?
[quoted text clipped - 5 lines]
> believe it or not, the oxygen sensor. But vacuum leaks are high on the
> list.

Signature

Who needs a life when you've got Unix? :-)
Email: john@unixnerd.demon.co.uk, John G.Burns B.Eng, Bonny Scotland
Web : http://www.unixnerd.demon.co.uk - The Ultimate BMW Homepage!
Need Sun or HP Unix kit? http://www.unixnerd.demon.co.uk/unix.html
www.Strathspey.co.uk - Quality Binoculars at a Sensible price

Reply to this Message

Tony - 21 Apr 2009 11:29 GMT

> I agree with Scott, good chance it's a vacuum leak. Most likely one is a
> ripped hose from the throttle body to the air flow sensor (the biggest
[quoted text clipped - 12 lines]
>> believe it or not, the oxygen sensor. But vacuum leaks are high on the
>> list.

We did a basic service for oil, oil filter, air filter recently but
spark plugs no and fuel filter no. I agree these should be done anyway,
but I just thought that as all other gears accelerate normally it wasn't
a fuel/spark problem, but you never can be sure.

I don't know the milage, probably around 90Kmiles. He's kind of running
the car into the ground, but is prepared to do whatever is needed. I
know this is not a good attitude but he doesn't have alot of money, and
isn't really into cars. I try to explain that a newer car will be more
expensive than good maintenance but most people just don't get this.

I will have a look at the vacuum hose the next time I see it. Thanks
for the help, I'll post an update if anything to report.

--
Tony

Reply to this Message

Tony - 28 Apr 2009 15:31 GMT

>> I agree with Scott, good chance it's a vacuum leak. Most likely one is a
>> ripped hose from the throttle body to the air flow sensor (the biggest
[quoted text clipped - 26 lines]
> I will have a look at the vacuum hose the next time I see it. Thanks
> for the help, I'll post an update if anything to report.

The owner says he can see cracks in a inlet rubber duct, seems to be the
likely cause. Thanks for the suggestions, they really helped.

--
Tony

Reply to this Message