View Full Version : Please Help Random rough running...any ideas?
adrianwillis
04-05-2012, 08:54 PM
Audi A4 B5 1996, 1.8 ADR petrol.
I've been having intermittant problems recently where the car runs absolutely fine, then runs really rough (as though it's misfiring, popping and spluttering with very little power) then it runs smoothly again, then goes through a rough patch...and so on.
I've changed the following parts already:
Spark plugs
coolant temperature sensor
air filter
throttle body (it adapted perfectly)
I took it out for a run after changing the throttle body and all appeared well (there were a couple of isolated stutters) until I sat on the drive with the car at idle...then it progressively started to run rougher and rougher, and was "missing" when I blipped the throttle, or increased engine revs slightly, then it would smooth itself out for a while before it started to run rough again.
I'm not sure where to look next.
VAG-COM shows no error codes at all.
I replaced the camshaft, and spark plug oil gasgets the other day and also checked all of the breather system...all OK.
It seems as though another sensor might be on the blink, sending wrong messages to the ECU every now and again?
Has anyone got any ideas what could be wrong?
Thanks in advance for any replies.
Chesp123
04-05-2012, 09:27 PM
I had similar symptoms with rough idling and it turned out to be the cambelt. Its worth getting it checked to rule it out.
fourringsrus
04-05-2012, 09:54 PM
Fuel filter and lines good ?
adrianwillis
04-05-2012, 10:40 PM
Fuel filter hasn't been changed for probably 10 years.
Would a blocked fuel filter cause this random rough running?
zollaf
04-05-2012, 10:41 PM
yes
adrianwillis
04-05-2012, 10:56 PM
Where is it located on a B5 saloon?
fourringsrus
05-05-2012, 09:55 AM
Don't know the layout on the B5, but quite often if not in the engine bay there will be a filter can positioned up against the floorpan on the outside of the car, somewhere around the rear axle and underside of the fuel tank area.
If a decent constant supply of fuel can not get to the engine, it " aint gonna work".
Not expensive or difficult to change
Good luck
Stuart
zollaf
05-05-2012, 10:00 AM
when trying to get to the bottom of a problem like this you need to do the basics first, all filters and other service items. when you know they are right then you start looking deeper. sometimes the silliest and most overlooked things can end up with you emptying your wallet and pulling your hair out.
iirc you will find your filter just in front of the rear axle as 4x0's says.
adrianwillis
05-05-2012, 01:49 PM
Fitted a new fuel filter...the problem persists!
When I started the car from stone cold it ran smoothly...the problem of very lumpy running appaered after about 1 mile and got worse...so it seems that this problem is associated with the engine getting warmer.
It was so bad that it struggled to get up a slight hill near our house.
This problem was less apparent when I took it out yesterday...it started behaving badly when I was sat on the drive with the engine at normal temperature.
What should I investigate next???
I've got VAG-COM so I can look at measuring blocks etc and this might highlight the problem, but I don't know which blocks to look at.
There are no fault codes on the engine after this morning's outing.
I'd really appreciate some sage advice.
Thanks in advance.
Ade
zollaf
05-05-2012, 01:54 PM
does it have coil packs or ht leads ?
adrianwillis
05-05-2012, 02:48 PM
It has one coil pack that bolts on top of numbers 3 & 4 cylinders, wth ht leads out of the pack to cylinders 1 & 2...interesting you should ask this...last week I replaced the camshaft cover gasket and spark plug gasket because my spark plug tubes were full of engine oil.
I cleaned the coil pack and leads etc after I'd replaced the gaskets.
I have read somewhere that this type of leak can be the kiss of death to the coil pack, so I wonder if mine's on its way out or if an HT lead needs replacing???
Would vag-com shed any light on this?
Thanks for your replies...really appreciate them.
Cheers.
Ade
zollaf
05-05-2012, 06:40 PM
oil rots rubber, so i would try replacing the leads first and see if it makes a difference. not sure on yours whether a misfire will be picked up on diagnostics or not.
adrianwillis
05-05-2012, 07:57 PM
Vag-com doesn't seem to pick up misfires on my B5.
I've come to a similar conclusion that either the coil or the leads are suspect...all 4 spark plug tubes were full of oil and the rubber insulators have all perished as a result.
It's possible that the oil has travelled into the leads or that the coil has been too hot and started to fail, or it's been working overtime trying to combat the oil soaking.
The engine is backfiring a little on overrun so that suggests the fuel/air mixture isn't being ignited at times, and this may well be down to poor sparks or no sparks at all at times.
I've got a replacement set coming next week after sourcing the coil and leads from a breaker on eBay, so we'll see what happens when it arrives - I'll post another message to let everyone know.
Ade.
mumutley
06-05-2012, 10:58 PM
Hi
Does it use any oil or water?
Have you carried out a compression test? (if possible do this when the engine is cold (you state runs ok till it gets warm) then take car for a run and being very careful carry out another compression test)
Jeremy23
06-05-2012, 11:43 PM
Did you calibrate the new throttle body when you fitted it?
adrianwillis
10-05-2012, 09:56 AM
I used VAG-COM to adapt the new throttle body and this seemed to work fine...the old fault code disappeared instantly when I "cleared codes" and the new TB adapted within a few seconds of running it on block 098.
I'm waiting for a replacement coil and leads to arrive...fingers crossed!
PS...the only oil and water the car uses is what it leaks! I've sorted out the oil leak now by fitting a new camshaft cover oil seal, and I know where my slight water leak is coming from...soon to be fixed.
Ade
adrianwillis
11-05-2012, 02:41 PM
Replacement coil pack fitted (or is it an ignition control module?) and the engine is absolutely fine now...so that was the problem after all!
It appears that the coil pack / ignition control module had either come to the end of its life or it had become compromised by all 4 plugs and connectors having bathed in hot engine oil for several months.
Thank you to everyone who replied to this thread...I hope it might help someone else who has a similar experience to me.
Cheers.
Ade
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