1.2 tdi starting problems when warm and stops sometimes on idle

Wheelie

Member
Hi all,

I bought my A2 1.2 tdi (2002, 180k km) few months ago. It had broken hydraulic pump
which was changed (almost no brakes and turbo stopped randomly) and new fuel filter (genuine Audi part)
was changed. Oil and other filters was changed.

Now there is only starting problem left. Start/Stop doesn't work. It stops, but very rarely
starts so I have to drive with eco off. It tries to start a little, but then gives up.

Normal starting (cold engine) works by turning key for about 10sec or it fires and stops
and I have to start again. When it starts to run it works ok.

When engine is warm and stopped for half an hour starting may take tens of tries or it is
impossible to start. It fires and stops or doesn't even fire.

Quick stop and start (within few minutes) works as well as with cold engine.

Two times engine has stopped from idle after running motorway for 15km. Then I was
using eco mode. It took long time to start again after these shutdowns.

My mechanic (who knows VAG cars quite well) says that there is a leak in fuel system, but as
it was not fuel filter and lines look ok it must be injectors. He says that usually new injector seals
wont fix the problem. His/their experience is that changing seals usually makes things worse
because bores are/get loose on this engine type. They haven't opened engine yet.

I'd like to get second opinion on this and ideas what else could be causing this problem with starting.
What are my chances to get a working car by injector seals change?

Otherwise car feels good. There is no error codes from ECU. Consumption was 3.1l/100km on my
daily trip to work and back. Now consumption is almost 5l/100km because weather (-20 to -27°C)
and I haven't used eco mode after those stops from idle.
 
I think one of our 1.2 experts will be along shortly with some helpful advice.

Welcome to our club.

Steve B
 
When you say it took a long time to start do you mean that the car tried to start and did not manage or that the system did nothing?
Also what temperature was it when this happened?

Does the car start easily in -15c or lower or is the start a bit rougher than usual?
 
I checked my glow plugs on 95000 miles for the first time - two were not working !

That will help! But once warmed up, you shouldn't need them anyway. Stop/start does work if it stops! I would investigate the fuel system, particularly filter and possibly the pump (on the end of the camshaft). I don't think that this has anything to do with it being a 1.2.

RAB
 
That will help! But once warmed up, you shouldn't need them anyway. Stop/start does work if it stops! I would investigate the fuel system, particularly filter and possibly the pump (on the end of the camshaft). I don't think that this has anything to do with it being a 1.2.

RAB


In that case could it also be a possible temperature sender failure?

Thank for the input RAB.

Steve B
 
Hi,

From the faults you describe I would be changing/checking the readings from the coolant temperature sensor.

Also, it is no bad thing to change the glow plugs. Although in theory they shouldn't come into play when the vehicle is warm, we have seen several cases where an open circuit glow plug has caused various starting issues. We believe a faulty plug can confuse the control logic in the ECU and cause issues you wouldn't expect them to cause! We've seen this on several tdi's.

The brake light switch may also be a good one to check.

A fuel system issue is possible, but if the filter has been renewed correctly with a genuine example, I'd definately be checking the cheaper/easier items listed above before further exploring the fuel system.

Cheers

Rob.
 
Could it be that you have water in the diesel, which is freezing and blocking/partially blocking fuel flow? If it is still freezing, loosen the filter drain. If nothing comes out, you have water in the diesel.

RAB
 
Thank you for your answers and suggestions.

I will ask my mechanic to check coolant temp. sensor and check or change glow plugs. I also
googled a little more and found that one possible reason for tdi not starting while warm is cranckshaft sensor.
I think it fits quite well to my symptoms. There was a good example on this forum, but I can't
find it anymore.

I will forget the fuel system for a while and go with these. I will report here what was done and if it helped.

I forgot to mention that brake switch was also changed as it was cheap and easy to change. Problem was not there.

I have started once succesfully from -17°C. Once I tried from -26°C, but it didn't start. Starter
spinned engine, but slower than normally. I tried something like three times
10sec and then stopped as startes was getting slower and I didn't want to exhaust my battery.
All other starts have been after using engine heater.
 
It would be worth checking the starter earth connection (i am assuming it is in the same place as a 1.4. i.e. In the right hand side of the engine bay).

That could slow the starter motor speed significantly if the connection is not clean, and that could make it harder to start.

Steve B
 
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Hi.just fixed the problem on my 1.2tdi but lupo.my problem was the injectors o-ring ,i replace those and now the problem is gone.i first checked the hoses for leaks then i started replacing the hoses from fuel filter to tank and f filter to engine with transparent hoses and realized that there was air in the sistem after 1min from starting the engine and the fuel sistem(hoses)wouldnt loose the air until the temp of diesel wasnt high enough .also check the plastic that goes in fuel filter wich make the hose conections.my car started normal only if i drove it until the air was gone .if i started the car and stoped it after 10-15min the i would crank the car for 10-20sec before would start again and i had poor idle and sometimes stopped ,that was becausr air was in sistem .i hope it will fix your car and sorry for my english
 
Hi Remus,

There is no need to apologise about your English, the fact that you posted help like this is great and your English was great too, probably better than mine even!!

Steve B
 
Little update.

My A2 was standing about a year. I had leave from work so I didn't need it for a while, but now I've driven it last three months.

(Almost) All possible sensors are changed. Sensors are easy to change and relatively cheap so I ordered them one by one and tested what
happens.

Tandem pump is changed and it has new seal. Fuel tank was checked and some non-return valves has been changed on fuel line. We
were trying to find source for air in fuel line, but could not find it. Then we thought if there is just a little air those air traps
in fuel system should take care of problem. There was no bubbles in fuel return hose, but symptoms indicate air in fuel system. I'm quite
sure when weather is cold (0C or less) problems start when fuel circulation change from "only in engine" to "return to tank" which happens
at +60C if I remember correctly.

Turbo along with pressure converters and solenoid valve is changed and EGR-valve is changed. It took very long time to start
after engine stopped while driving so we thought that turbo vanes are stuck. Battery was depleted couple of times before
engine started.

All parts are bosch or similar "premium" stuff.

Everything was ok for 250km and car was running nice after turbo was changed, but today it stopped on highway when I was rolling
on eco-mode. It had few hiccups on climb before this when I accelerated from 80 to 100km/h. This time engine started quite fast after few tries.

Starting problem when engine is warm persisted even after turbo change. It starts quite ok when cold or hot. Start&stop works randomly, last time I tested it didn't start.

Started was removed, checked, cleaned and re-installed. It works fast enough and is ok. Battery is fine too.

Injector were tested and they are working ok, but injector seals are mystery. I'd like change seals, but my mechanic says they have to be reseated and it usually just makes
problems worse if the problem is there...

Maybe I'll go with injector seals next. Any suggestions?

PS. I changed this to hobby project so I don't have to count the money. :)

...and pressure accumulator is new too.
 
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There is a sensor on the starter motor that protects the starter if it gets too hot. This can fail (after being intermittent) which means the starter won't work all the time, until it fails completely. The cure is to bypass this "box" on the end of the starter with a simple link. Both our Lupo's have failed in this way, but the starters are still working - one since 2003! Worth a try. You can't buy the sensor separately.

RAB
 
By stop/start not working, do you mean that STOP doesn't work? There a few things that would prevent STOP from taking place, including low temperatures and low battery voltage; all quite normal. By "start not working", do you mean the starter or that it doesn't fire?

RAB
 
Stop works ok when conditions are met and start tries to start engine for 0.1sec and usually fails.

Thermal relay prevents starter to working at all, but starter always runs. Engine just doesn't start.
Starter does sometimes stop before engine is even tries to start... I'll make a video of it today.
 
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The line from the fuel tank to the LP pump is always under vacuum. Check for air being drawn into the line, as this will cause similar symptoms. Injector looms OK?

RAB
 
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