Lumpy idle + juddering - FIXED

[jone23]

Along with many other people on this site, i have been pulling my hair out trying to fix the lumpy idle and slight hesitation on my 325i. It only really occured when warm, and under very light throttle but it was starting to really piss me off, after all this is supposed to be the finest of german automotive engineering but mine felt more like a 1 litre fiesta.

With the thanks of the zone i started to investigate things like air leaks between the throttle body and air flow meter, changing the fuel pressure regulator, changing the blue temperature sensor and changing the air flow meter to another one and nothing really made much of a difference. Then, yesterday i was browsing through old posts as i was really bored at work and found this thread:

http://www.e30zone.net/modules.php?name ... lling+road

About half way down the first page is a bit showing how getting a decent earth from the battery to the body/engine gained him 40 horses on the rollers and sorted some of his running issues- Apparently this bad earth caused a weak spark which meant the exhaust fumes smelled rich even thought the car actually wasn't running rich if you know what i mean.

Anyway, i got me thinking about my motor... Probably down on power, rich smelling exhaust fumes but returning 28 mpg, and the other running issues i mentioned earlier so i thought it give it a go. The other thing was before the winter i put on a new(er) battery that i knew was good but was a bit too small so i had to put another earth lead on the bridge the gap.

This was basically the problem.

Last night i replaced the battery with one that fitted and ensured the earth straps were in good nick and battery clamps were good and tight and voila, it feels like a new car!! It pulls a lot harder, runs a lot smoother and stops me looking a right twat kangerooing in traffic!

[fugazi33]

Cue hordes of jerky E30's owners running for the spanners
Cool it's sorted and will help a lot of other peoples running problems hopefully.

[jone23]

Well thought i'd share it with everyone, it was just so annoying and such an easy fix!

The thing is with EFI cars is that lots of people (including myself) just assume any running issue is a sensor/ wiring/ ECU problem. Often just getting the basics right is the answer.

[louis2035]

very interesting, my sport has been lumpy when idle for a while and pretty hesitant. i have checked all the pipes for leaks cleaned afm, icv and throttle body and spindle of shite. still no luck. its is definatley running rich, as exhaust fumes smell very strong.
i will try a new battery and earth lead tomorrow and let you know how i get on.

[Brianmoooore]

Just put a voltmeter between battery negative terminal, the car body, the engine block and the alternator body. Can show interesting results sometimes!

[louis2035]

been to get a battery, didnt realise how expensive they are. will need to wait a few weeks until my wallet looks a bit healthier.

[jone23]

I don't think it was neccessarily the "new" battery that did it, i think it was just cleaning the earthing points and ensuring all major connections were good and tight...

I went out again in it again at lunch time and i'm definitely not imagining this, it really does feel so much better!!

Jon

[tailoutcharlie]

am a bit of a spanner when it comes to spanners.

as the bat is in the boot, where and what exactly do i have to check, and is any of this checkable without disconnecting the battery as the alarm is a bitch to turn off.



edit. stupid idea i'll kill myself i know it.

[Giggz]

That is some really useful info there as every other thread popping up in the tech section is complaints of 'lumpy idle'. Mine is doing it at the moment now also. Will try this possible solution. Hope it works, only is it more difficult to figure out if the battery is in the boot as mine is? It also has that device attached to the battery where you pull a "key" out and the battery is then dis-connected.

Apologise for jacking your thread by the way...

[tailoutcharlie]

spoke to the guys at local garage. apparently the prob earth cable is only six inches and connects the bottom of engine to the chassis leg. right at bottom so it gets corroded as feck.

am changin it on fri along with bushes and an e36 steering rack. will let you all know how the car feels.

[Brianmoooore]

spoke to the guys at local garage. apparently the prob earth cable is only six inches and connects the bottom of engine to the chassis leg. right at bottom so it gets corroded as feck.

Any problems with that strap, and it will get extremely hot when cranking the engine.

[tailoutcharlie]

would you suggest putting in a new earth higher up the engine bay then??

hard to check for these things on the street, car is quite low. anyway i can check it out from above???

ignore that first line, long day=brain dead!!!

[Brianmoooore]

The OE earth strap, in good condition, and assembled with a little copper grease is all that's required.
You can easily check the strap from above if you undo the two nuts and hose clamp that holds the air filter/AFM in place.

[tailoutcharlie]

great.

should be rather easy on mine, airbox is long gone. i love these cheap easy fixes that make sutch a huge difference to the car.
long live the zone!!!

cheers brianmooooore

[Brianmoooore]

should be rather easy on mine, airbox is long gone.

Well put it back and gain a cheap BHP or two!