1.8t startup problems

myth

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Hello all,

My girlfriend has bought an 2002 audi a3 1.8t aum engine and has a random start up problem.

The problem is very rare, maybe just twice per month, but when it happens, when she starts the engine, it stutters very violently, like it-s about to blow up.

Sometimes the engine dies and she has to restart the engine and everything is perfect. Sometimes the engine is barely running, but after 5 seconds it recovers and the engine runs well.

She always waits till the fuel pump in tank shuts off, then switches on the engine. There are no fault codes stored.

This issue is only when its starting the engine. There are no issues while the engine is running, idle is fine, pulls like a train...

Appreciate your help!
 
How have you tested for faults? Using VCDS or android torque (or similar) VCDS usually stored more codes. It sounds like a misfire of sorts.
 
Yes, I did scan with vagcom and there are no fault codes.
 
I had same problem sometimes when engine is cold (mornings in winter) car was working on 2 sometimes on 3 cylinders sound is awful. I changed ignition coils all four and no problems so far. I have 1.8t agu mark


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Soulnd't an ignition coil throw a knock fault code?

Just discovered another symptom: the engine fires up, but has absolutely no power. If you try to move the car, it just dies, restart the engine and everything is fine...
 
After 2 weeks of no more the issue, I can say I have solved it by replacing the fuel pump inside the tank.
 
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So the problem is now back. As the temperature is now close to 0 degrees, the engine barely starts in the morning.

So, you turn the key, it fires up but it seems to be firing on 2 or 3 cylinders and it shakes a lot, or even stalls. Second or third start up and everything is back to normal.

OR the engine runs at 1000rpm but if you want to put it in first gear, the engine has no power and engine stalls.

This past week, the problem occurred every single morning. It has no fault codes, last year I have changed the fuel pump, now I checked the fuel pressure. It's holding pressure, the fuel pressure regulator works fine.

I have no clue what to do next. Please help with advice!
 
So the problem is now back. As the temperature is now close to 0 degrees, the engine barely starts in the morning.

So, you turn the key, it fires up but it seems to be firing on 2 or 3 cylinders and it shakes a lot, or even stalls. Second or third start up and everything is back to normal.

OR the engine runs at 1000rpm but if you want to put it in first gear, the engine has no power and engine stalls.

This past week, the problem occurred every single morning. It has no fault codes, last year I have changed the fuel pump, now I checked the fuel pressure. It's holding pressure, the fuel pressure regulator works fine.

I have no clue what to do next. Please help with advice!
My engine used to shake violently at one point I noticed two fuel injectors werent pushed in properly..I popped em back in and car ran great
 
Hey mate, I've also got an AUM and had this issue fairly regularly and found that unplugging my failing SAI pump fixed the problem. I have left it in situ so there's no need to play around with the piping until I get the time to remove it entirely.
This is totally anecdotal, but I recommend unplugging it before the next cold start, could be a really easy fix!
 
Seconday air pump? The one that's pushing air into the exhaust? Hmm, I will try to unplug it, but it could be the secondary air valve(the one way valve) faulty.

Thanks for the tip. Will check and let you know!

@Asim1, high unlikely. If there were problems with injectors not being seated properly, I would have had problems during high loads, high rpm, or even at idle. My problem is only when cold start.
 
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Seconday air pump? The one that's pushing air into the exhaust? Hmm, I will try to unplug it, but it could be the secondary air valve(the one way valve) faulty.

Thanks for the tip. Will check and let you know!

@Asim1, high unlikely. If there were problems with injectors not being seated properly, I would have had problems during high loads, high rpm, or even at idle. My problem is only when cold start.
No worries just sharing my experience
 
So today it did it again. So it's not the SAI. Started the engine for aprox 1 min, then put it in gear and wanted to move. The engine stared to shake and turned it off. Switched it on again and then it worked fine.
 
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Sounds like it’s not running on all cylinders. Have you tried new coils yet? Having said that, I’d have thought you would get a code if that was the case. Might be worth a try borrowing some known good ones if possible??
 
When pulling away you are requesting load and if the engine needs air, the MAF might be on it's way out, try unplugging the MAF and see if that makes a difference.
 
I have put new spark plugs and other know good coils. Still have old coils though, but no difference.

If it would be the MAF, why would only give bad info to ecu when cold? And it's not like it has time to heat up or something, cause in a matter of a minute or so the engine is back to normal.
 
The engine requires a lot of air when cold it runs rich and with big advance.
 
So it's been 4 days since I have changed the ECU. So far the problem did not reappear and the vibration at idle is significantly dimmed.
 
You changed the ECU? . How did you decide the ECU was faulty ?
 
I didn't. My brother had one laying around and said: change it and see what happens. I had my doubts anyway. I would have never guessed that the vibration is due to ECU...
 
Lucky it had the immo disabled. ECU's are normally pretty much bulletproof and don't go wrong that often. You were lucky there.
 

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