Flat spots on acceleration

[Mease]

My Audi 80 2.0 '92 has flat spots when accelerating. This occurs at just under 2000rpm and again at around 3000rpm but revs freely at stand still.
This is more apparent when the engine is cold but tends to dissappear when the temp is up to about 110c.

As a matter of course I changed the spark plugs, leads, dis. cap and rotor arm but problem is still there.

I've checked the lambda probe fuse - is ok

I'm thinking of changing the thermostat (as problem goes away when temp is up)

Could there be anything else worth checking?

Regards

[Mease]

Update 1#

I have had a new thermostat fitted...and guess what...although the engine seems to get to temp. quicker the initial problem still persists.:aargh4:

I am booking the car in for a computer diagnostic..results to follow!

[Mease]

Update 2#

Well I got 3 error codes.
1. relating to a low oil pressure warning, I remember this.
2. one related to something to with the manifold(?)
3. this one highlighted a lambda probe problem. We reckon this to be more likely the culprit for my problems. We put a multimeter by it and apparently the probe was giving a reading half what it should be.

The codes got reset.

I will be replacing the lambda probe next and will keep you updated!

[Mease]

:approve: As promised the the third and final update of my 'flat spots on acceleration' problem.

Now, throughout this forum there are several references to dodgey lambda probes/fuses but the problems that were associated with these references didn't quite hit the nail on the head for me!

Anyways, I disconnected my lambda probe and guess what?...yes no more flat spots under acceleration. Unfortunateley its not recommended to run your motor like this indefinately so I replaced said probe with a new one £52 from GSF www.gsfcarparts.com (http://www.gsfcarparts.com)

Now the motor is running great, no more flat spots and I'm probably getting better economy also.

Now all I've got left is a poxy dribble of coolant from where the temperature sensor housing joins the engine block...:(

Later!

[stuart]

Hi

Thanks for keeping us updated, and I am glad you have sorted your problem.

Stuart

[anthonyian]

I have an Audi 1.6 (M Reg). After reading about your problems concerning acceleration, my car has the same problem, unfortunately I'm not sure if my car has a lambda probe, so if it hasn't, any idea what could be causing the same said problems.

As usual

Any help greatly appreciated (much appreciated)

[Mease]

Anthonyian
Please remember that I'm not a mechanic and arrived at my conclusion by going through a process of elimination as described in my updates.

I think that most if not all cars have a lambda probe these days. Its got something to do with measuring the amount of oxygen remaining in the exhaust gases to allow the ECU to control the combustion efficiency and make alterations if the mixture is too rich or too lean. The idea is to give the best possible fuel economy and lowest possible exhaust emissions.

It might be worth you getting your ECU scanned as this may indicate the problem area without going through unneccessary expense.

Hope this helps and good luck

[anthonyian]

Hi

I have the same problem with my audi 1.6 M. I too have changed all the electrics, but still no differance. I even had a diagnostic and everything according to that was ok. I have an appointment in a couple of weeks to have industrial cleaner put through my injectors. what they do is disconnect the fuel from the tank and then run the fuel line (at the top of the engine) to a 5 liter bottle of injector cleaner and run the engine for an hour or until the bottel is empty. If efter that it still does it then i am going to flush the engine out. I don't meant add flush to the existing oil but to flush it out properley. because I am beginning to think its an internal thing, something has to be sticking inside the engine, maybe an 'oil clot' (like a blood clot) but it has jammed somewhere. i hope someone comes up with a proper answrer soon because i am running out of ideas.

This is the same problem i have had since my last posting last september and its still not solved

[andycraze]

hey guys same problem here i have a bora 2000 reg 1.6 16v, acceleration shutters between 2000 and 2500 revs mostly just after 2000, i was wondering what could be the problem as revs are otherwise ok and are constant when idle and acceleration is ok

also when i take my food off the acceleration pedal the engine shutters and acceleration goes down, it should go down but before this it shutters shaking the whole car...could it be connected with the acceleration shuttering between 2000-2500?

any ideas bora petrol mechanics? thanks, andy

[Jillbaby]

Hi everyone, am new here today, and a mere female so go easy on the technicals :o. Have been reading these posts with interest as I have a late M reg Audi 80 2.0E with this stuttering problem. It's been going on since last summer, and to date 2 garages have looked at it and done the diagnostic tests etc. Also checked the obvious plugs, leads etc and replaced rotor arm and idle control valve. Guess what - it's still happening, just as you say - at around 2500-3000 revs, almost constantly when cruising at 3000ish. A relief to find others with similar - I was beginning to think the garage thought it was just in my head! A friend said he thought it could be to do with the ignition amplifier? This lambda probe interests me - if there was a prob with it, surely it would have shown up on my diag tests? When the stuttering's really bad there's also a really bad exhaust smell - not the usual cat, bad-eggy smell but putrid and poisonous - assume this is connected in some way?

The bills are running up, and I just want my little car to get its poke back! Also, as yet I haven't had a bill from my garage for the two vists - surely I shouldn't get charged if they haven't fixed the prob?
:1zhelp:

[scotty33]

You can test a lambda probe yourself, or have a garage do it.

locate the probe itself, usually mounted on the front of the catalyst or the exhaust manifold. You will need a multimeter set to volts/millivolts or a voltmeter.

The engine needs to be warmed up to temperature for the test to work

The lambda sensor wiring plug needs to remain connected to the car's wiring harness.

follow the wires from the lambda sensor back to the wiring connector plug. There are usually 3 wires, 2 are usually white (these are the heater circuit) and the other wire (maybe black?) is the signal wire.

At the connector plug, peel back the rubber gaiter (waterseal) and identify the signal wire.

Push the positive multimeter lead/probe into the back of the signal wire connector, the negative meter lead/probe needs to go to a good earth.

You should see the signal 'oscillating' between approx 0.2 volts rising to approx 0.9 volts. It should do this once per second. If it is slower than this, the lambda probe is still working but not efficiently.

If the reading is steady, the probe is bad. If the reading is not in this range, there may be a short from the heater circuit wires, which would result in seriously bad running. As mentioned above, the heater circuit needs to be working properly, so check the fuse is ok for the lambda probe.


If you are interested, stoichiometric fuelling (air fuel ratio of 14.7:1 which gives the most complete combustion) usually equates to 0.5 volts. The ECU is not able to maintain the mixture at exactly this mix. Instead it has to monitor when the mixture is going weak (0.2v) then add more fuel until it goes rich (0.9v) The average ends up at 0.5v.
The lambda probe is not used by the ECU, until the coolant temp sender for the ECU shows that the engine is up to temperature.

I think it would be possible for a lambda probe to be faulty but not show up on a fault code read. I think the bad smell would be due to poor running, whether this be due to over fuelling or an electrical misfire, I'm not sure. But you should be able to rule out the lambda as above!

I would not be happy paying a garage for failing to cure a fault. But they have fitted some new parts which may have been worn. Why did they change the Idle control valve, do you have idling issues? The lambda probe can cause problems at idle (only when warmed up), usually causes poor mpg too.

[Jillbaby]

Hi Scotty33 thanks for the info - not that I understood most of it! Will pass it on to someone who will. Don't ask me why they replaced the idle control valve - the replacements (that and the rotor arm) they have done were in an attempt to solve this juddering problem. I have also posted on another thread (look for my posts by my handle and you'll find it) and someone there seems to have permanently solved the same problem by locating and resoldering a dry joint. I am going to try this - if this is the problem it will stick in my craw to pay what is likely to be a vast amount for not fixing the prob! None of the work they have done has permanently fixed it - the most I got was about 3 days of judder-free motoring before Christmas and then it went back to being as bad as before. Hm, I suppose I'll just have to bat my eyelids again LOL. It will be good to go in and quote them some technicals as I think they have written me off as a daft ignorant female. Having said that, they came highly recommended by several friends, so they are no cowboy outfit - I think they are genuinely perplexed by this. I'll feel great if I can fix it myself though! Thanks again

[scotty33]

No need to flutter the lashes - quote the sale of goods act! goods and services must be of satisfactory quality and fit for purpose.
To be fair to the garage, the ECU relay cutting out is basically the same as turning the ignition off, so no real way of knowing it would be at fault without replacing it.
I happen to have an ECU relay from a passat 2.0, which I stripped down, a few years ago. A dry joint would usually show as powdery residue around the soldered 'spots' on the circuit board.
Pic
http://i246.photobucket.com/albums/gg104/scotty33_bucket/SSM10694.jpg
http://i246.photobucket.com/albums/gg104/scotty33_bucket/SSM10693.jpg

[Jillbaby]

Crikey, I never thought all this could be so interesting LOL. Thanks again and I'll let you know what happens when I can get around to getting the joints checked out :o)

[chronic]

thanks so much i'm gona give that a go as i have replaced the same parts as u to still have the flat spots.I shall report once bought and fitted.:beerchug:

[Jillbaby]

Hi Scotty33 - I (well, not me, but a man I know lol) checked the relay last week and indeed some joints were dry. Took about 10 minutes work to resolder all of them and since then the car has run like a dream. After about 7 months, 3 trips to the garage and much swearing, my baby's got its poke back at last! Think this ought to be in the standard checklist for this problem since so many Audi owners seem to have encountered it. I have put this news on the other thread about juddering and it's really all down to SteveInDaBury who discovered the cure - I owe him a pint and the same to you when you're next in Hampshire for providing the pics! Thanks mate. Everyone take note - if you have this problem, check the joints first and save yourself hassle and expensive and fruitless trips to the garage. It's so easy even a girly girl like me could have done it, if I'd had a soldering iron, but then again, why keep a dog and bark yourself? LOL

[scotty33]

What a result! :beerchug:for the kind words and thanks for letting us know how you got on. Time to start enjoying the car now:D