Audi A3 1.6 8L AKL – Power loss when 'accelerating'

[trapdoorsally]

Audi A3 1999
1.6 8L (AKL engine)
80,000 miles
Hi all, I have been an avid voyeur of this site for a while (to the point of being quite an obsessive recently) as I try to pinpoint a diagnosis/solution to my limping Audi A3.

• Car drives poorly on acceleration, bunny-hopping when engine is warm (approx. 2 minutes into any journey).
• Intermittent stalling when idle in traffic (there is never any warning when this happens, revs just drop out). However the idle is fairly stable.
• Car also appears to decelerate very quickly when the accelerator is released.
• Revs appear to increase when the clutch is depressed (could be simply a faulty clutch switch?)

The issue first happened about 10 months ago; having driven 10 miles (a relatively long distance on the Isle of Wight) without issue but then struggled to start it on my return an hour or so later, it then took several cranks to eventually start but was horrible to drive (lumpy with no power). The issue was much worse in lower gears/higher revs and only smoothed out once in the higher gears when I could eventually pick up speed; however it was present again when pulling away at junctions.
This problem was only ever intermittent until a couple of months ago following my MOT when I believe it became much more frequent. Nothing carried out on the MOT should have caused any fault described above as it was mainly structural work, although the mechanic mentioned he’d topped up the coolant as it was very low (which surprised me)*.
The poor performance appears to initiate around 3,000rpms but is then present throughout the entire range. This now happens every time I drive the car.
* I’ve watched the coolant level closely since and it hasn’t moved - although obviously I haven’t been driving it quite as often as I normally would.
Mainly on advice from previous threads of similar faults:

• I replaced the breather pipe as the original had perished at the connection from the bottom of oil reservoir; this had covered much of the engine in oil.
• Replaced the spark plugs – old plugs looked okay although one had small amount of oil/fuel on it.
• Changed the HT leads and the coil pack. (2^nd hand)
• Cleaned the throttle body – which wasn’t particularly dirty.
• I replaced a leaking vacuum hose on the brake servo line.
• Cleaned Mass Air Flow sensor to no avail……..then replaced it. (2^nd hand)

I also took the car to my local Audi dealership who told me there was nothing wrong with it as no codes were present and the car had driven fine during two test drives – although then going on to say that it had stalled when they had it on the ramps! Out of courtesy they did check the fuel filter and said it was all clear (I haven’t checked this).
What I was looking into next (cheapest to most expensive):

• Injector cleaner.
• Crankshaft sensor.
• Fuel pump.
• Throttle position sensor (integrated into throttle body).

Please bear in mind that I’ve never been particularly mechanically minded – any advice would be great but you may have to draw a very descriptive picture and not use TLA’s (three letter acronyms).
I can’t afford to throw much more money at it as I want to sell it on with some value attached and with a clear conscience.
I also don’t want to take it back to Audi as they appear to have been an expensive waste of money. Whilst it’s been enjoyable playing around under the bonnet with my Haynes manual at my side it’s now becoming annoying and expensive trying to diagnose this.
I have a good friend (local RAC man) taking a look at it soon also so I can update you with any feedback he gives.

[Wayne2000]

Did you change the Crankshaft sensor? I think that is what is wrong with mine, I am changing in on Monday, will let you know how I get on.

I have similar problems to you, engine not ticking over properly feels lumpy and loss of power if I accelerate, especially in 2nd gear.

[a3_agn_1.8_01m]

After you changed the MAF, did you reset the ECU? The MAF is a resistance based part, and just swapping it I suspect would not solve the problem entierly. It is a really sensitive part of the fuel system. You must have fuel pressure in the car, but after that the MAF is the one who decides how much petrol to put into your engine.

[trapdoorsally]

Apologies for the delayed response as I've been away working and left the car with the a garage to sort out.
It was indeed the crankshaft sensor which fixed the main issue of losing power but they are now struggling to remedy a problem relating to the revs which are remaining high on idle (1200) and generally playing up.
They've replaced the throttle body and temp sensor following fault codes but had a call today to ask If I could pop down to them so they can show me the issue...... I'll report back.
They are using a Snap-on diagnosis kit to try to align it correctly?

Many thanks for the suggestions/ replies.

Update
The revs on start up remain stable at around 900rpm a little higher than normal but I can live with that, the issue is when the throttle is engaged they don't then drop below 1100 rpm which has the garage stumped.
They've also ended up putting the original TB back on which leaves me with a 'new' yet 2nd hand TB to get rid of at a loss.
Any ideas?
I'm happy to sell the car on with this ' minor issue' but would love to get to the bottom of it if possible

[Alan02]

It may also be worth checking for an Induction air leak ( Engine drawing in un-metered air) upstream of the Throttle Body all the way to the Inlet Manifold gasket and any off-takes on the manifold etc.(for vacuum pipes).

[trapdoorsally]

It may also be worth checking for an Induction air leak ( Engine drawing in un-metered air) upstream of the Throttle Body all the way to the Inlet Manifold gasket and any off-takes on the manifold etc.(for vacuum pipes).

Thanks Alan I'll take a look.
There appears to be a flat spot when changing from 1st to 2nd gear which must be related also? Could well be a leak somewhere?

[audiA31.61999]

Hi Mate,

did you get to the bottom of this by any chance, I have basically done the exact same as you in replacing parts and a bit extra, tearing my hair out to pinpoint my issue.