The 'my car won't start' recap

RE: this thread

I've just booked the car in for the 3rd or 4th time at Audi for what I imagine will be the 'final showdown' with regards to my starting issues and their successive failure to fix it - and I'd like to be able to present them with everything we think it could be since theres more collective A2 wisdom here than any Audi dealer!

The symptoms -

Car cranks but does not 'fire'
Starts fine from cold
Happens generally when the car has been sitting between 5-40 minutes, but has been driven enough to warm up
Extremely hot weather seems to cause problem
Can start the car after multiple attempts and plenty of throttle bashing, often followed by smell of petrol or smoke from exhaust
Car sometimes unable to maintain steady RPM
Engine management light/EPC is intermittent

What has been done -

Full timing belt kit (April)
Lambda probe
Spark plugs
Recalibration of lambda probe and spark plugs

What it could be -

After much reading and research, I have:
Faulty crankshaft position sensor
Faulty camshaft position sensor
Dirty throttle body
A combination of these
(I suspect dealer hasn't checked these if they aren't giving error codes...)



Anything I'm missing? My current no.1 suspect is the crank sensor.
Cheers

Does your car still stall as you mentioned in the original thread or once the car is eventually started it's fine?

Click to expand...

Not as such, although a few weeks ago, it died 3 times consecutively straight after starting (badly). This was when I was trying to pull out into a fairly busy road. We were left stranded in the middle of it and my girlfriend had to get out and push us back into the space - so in a sense this problem is now becoming dangerous.

Throttle body clean has been on my to-do list but lack of vagcom has stopped me

I second ULP on the throttle body.

I'd also add fuel line/filter or fuel supply related to the list of possible candidates. I'd start with a full tank of v-power first. If you want buy some fuel additives and pour into the tank. I'm not normally a believer of additives but I'd cautiously suggest BG44K, I have a can sitting at home. My bro-in-law used it on his Jazz and said it did make a difference and seems to be a popular product with his customers keep coming back for it. I have no idea or proof but you could try other brands too.

Next, throttle body clean. Followed by fuel filter change. Then the sensors. Lambda actually does not affect it at all, if the ECU detects a fault, it reverts to a standard map with lowered performance and economy but it will start and drive and certainly no problem holding rev.

Thanks for the suggestions. Fuel system is one I'd ruled out after trying 98 octane a couple of months back with no real effect, but I'll stick fuel filter on the list.

I had a feeling the lamda probe probably wasn't the issue when I had it done, but it actually failed around the time it was at the dealers anyway so it 'had to be done'

Update

Well... I'm going to cautiously call this one solved something for anyone with similar symptoms to consider:

Two days in the garage and one new coolant temperature sensor later we seem to have a solution as I haven't had the problem since collecting the car. Dealer decided that it must be sending incorrect readings and thinking the engine was much cooler than it was causing the ECU to dump a load of fuel into the cylinders when starting resulting in a poor fuel/air mix. Makes sense to me and explains the smoke/smell issues that I had noticed.

£140 of work done for £0, and two days in a fantastic A3 TDI S-line DSG all courtesy of Tyneside Audi (didn't want to give it back!).

That's great The temp sensors do seem to go fairly frequently (although on TDIs the effects are less)

I would think throttle body clean should be first port of call. Mine was transformed after being done. Had it done by local Audi specialist who charged £60 (18 months ago) Money well spent as I didnt fancy doing it myself. Cheers Colin

Hope the replacement coolant sensor fixed it!
I presume the diagnostic checks they ran did not find a fault - ie the sensor readings were still within an acceptable range.
This is where an old-fashioned 'fault-tree' would be good, so each potential cause can be worked-through / eliminated. I think it is something we have mentally, but not on paper.
btw. I had a similar fault on an Italian car many years ago - the coolant sensor sent a 'cold engine' message, so the idle speed was set to ~2000 rpm. Quite exciting if you are in 5th gear! I think modern DFMEA (Design Failure Mode / Effect Analysis) techniques would prevent this nowadays.

Mark