Cold start misfire stalling rough running tappety...

[Adam Madrid]

HI everyone,

1999 2.5 tdi AFB A4. quattro

This problem is only in cold weather - sub 8C. It was fine over the summer and no problems at all but now the weather has dropped so has my car's happiness.

When I fire her up it starts quickly but immediately is running very loudly and tappety. The revs are not constant and is hunting. There is also a "jump" every 2 seconds which makes me think a misfire? I give her some revs to about 1500 for a minute or two to get her warmed up then move off. The car often stalls at lov revs in gear which makes it a problem as it's an automatic. It can stall a few times for the first 5 minutes or so until she is warmed up. If I rev her all the time using the manual gear selector then she wont stall but in D mode she can stall out at low revs.

When warm she purrs away nicely and has no problems idling at all with no stalling etc.

Any ideas?

I've run a bottle of the injector cleaner through and no joy. It's strange that it happens when cold but fine when warm.

Could it be worn cams?
Faulty injectors?
Glow plugs? but she starts fine and don't the plugs turn off after the engine is running?

 

[aragorn]

i'm not all that familar with the 2.5 engine, but it could be glowplug related. Its a 6 cylinder engine, and will happily start on 3 or 4 cylinders. Which would make it lumpy until the other cylinders have got hot enough to fire. The glowplugs do stay on after starting for a period of time until the engines built up some heat.

However given the issues continue for 5minutes or more i think perhaps not. Or its maybe a few seperate issues?

I would maybe check for fuel leaks. If its drawing in some air, it can take a good few minutes of running to clear it out.

 

[Adam Madrid]

Thanks for the reply.

Essentially I need to get it in my garage and look at the glow plugs, maybe the injector nozzles too and maybe the seals?

Would the air likely be getting into the injector seals or is it more likely to be the rubber hose fuel line?

This afternoon when I get in again I'll give it a really good rev to see if that gets air out of the system faster.

It will be the weekend before I get a chance to look under the hood.

Are there any colours I need to look for on the glow plugs when I pull them?

Thanks.

 

[Adam Madrid]

well... just tried it now.. ran it with foot on gas for 10 mins but was lumpy as hell. Couldn't even get out of the car park as it kept stalling. Looks like I'll have to call my insurance tow truck to take it to a garage. I hope it doesn't cost me a lot!!!

I'll give it another go for another 20 mins and hope that I can get it warm enough so that all cylinders are firing then get home. We'll see.

 

[Retroman]

My general experience of “cold start only” problems is that it is commonly linked to a either a failing MAF sensor or vacuum leak (unmetered air leak) downstream of the MAF sensor. When an engine warms up the coolant temperature sensor brings in post-combustion sensors in the exhaust which correct (in they can) an imperfect pre-combustion mix.

My experience of failing glow plugs is that engine running settles down very quickly after starting and that it does not take “minutes”.

You need to get the car plugged into some diagnostic software to pinpoint the problem.

 

[Adam Madrid]

Thanks for the response retroman! I did try in the car park for another 20 mins and got it to 70C then set off. It was fine as normal with no stalling.

Interestingly Im sure that my thermostat is stuck open as my car never gets temperature except on the motorway. I also disconnected the EGR a while ago which probably keeps it cooler.

Your description makes sense as after 40 mins of driving I put the heater on as I was cold and figured the engine was fine and warm. I noticed the gauge creep down to 60C then when I stopped at some lights it stalled again. I turned off the heater and it didnt stall again. So what you said seems to fit perfectly with my symptoms.

Tomorrow morning it will be about 2C outside so I'll sit in the car until it hits 70C then drive to work with the heater off. I'll let you know what happens.

Hopefully it is as you say either a leak in the pipe somewhere after the MAF or the MAF itself.

I do have VCDS but have just moved and will dig it out tomorrow.

I'll shop around for prices on that too.

 

[Retroman]

As your temperature gauge is showing that the engine struggles to get to (and maintain) a healthy operating temperature AND this is backed-up by the heater feeling cool – then this does tend to point to a faulty thermostat (and not a faulty gauge or coolant temperature sensor).

A faulty thermostat alone would not normally cause the running problems you describe. A basic, rough & ready test for the MAF is to disconnect it and start the cold engine without it. This will cause the ECU to adopt factory default settings and if the engine starts and runs better, this tends to point to the MAF being faulty.

 

[desertstorm]

Check the glow plugs, older engines usually have a few that have gone. It won't be your problem as they will have turned off within a minute or so of the engine starting but if they all go and it gets really cold the engine will struggle.
Your thermostat sounds like it may be stuck open.
The real core of your problem sounds like fuelling or lack of it. I would check for fault codes with VCDS. When was the last time the fuel filter was changed ?.
@adamss24 is the man to help with some ideas.

 

[Adam Madrid]

Fuel fitler was last changed 5 months ago as it was blocked!!! Might be again..

I unplugged the MAF this morning and it was still spluttering and stalling.

Fingers crossed it's the fuel filter then.

I'll keep you updated!

Thanks.

 

[aragorn]

sounds like air getting into the fuel, or a fuel blockage to me.

 

[Adam Madrid]

It just got towed to a local indy garage.. im waiting to get picked up snd I can hear the garage revving my car to bits! Let's hope they find the root cause and it's small!!

 

[Adam Madrid]

Im taking it to my usual garage. This one said he wants to get each injector tested for 50 each. So 300 just for testing, no cleaning. Then it's 200 per plug plus labour.

Im not happy with his 50 per plug "testing only" explanation. So I'll have an argument today with the insurance company who pay for the tow truck and get them to tow it to my garage. I only went to this garage as it was close to my work and they "trusted" that garage.

Maybe Im wrong about the testing figure?? Can anyone chime in and give me a cost for testing only?

 

[desertstorm]

How many miles has the car done? . Have they made any other checks as to what the problem could be or is this there idea as a start.
Parts for these engines are plentiful and cheap. You could probably buy a complete set of new injectors for a lot less than £1200.
There is a complete engine here second hand minus the turbo for £300
http://www.ebay.co.uk/itm/COMPLETE-...I-A4-B5-B6-A6-Allroad-C5-A8-D2-/172403728171?

http://www.ebay.co.uk/itm/audi-2-5-tdi-injectors-/182328344192?
http://www.ebay.co.uk/itm/AUDI-A6-V...NJECTORS-059130201A-059130202G-/252631541263?
Where abouts are you in the country ?

 

[Adam Madrid]

Cheers but Im in Madrid, Spain. Buying a tested set from ebay sounds lot cheaper than this garage. It's the 300 for testing only that got me fuming. Im not expert but that's way over the top.

 

[desertstorm]

Yes sounds like they may be taking advantage of you slightly. You could easily spend more than the cars worth if your not careful.

 

[Retroman]

Whole set of injectors "playing-up" when the engine is cold and working fine when the engine is warm - hmmm?

 

[aragorn]

Does it produce reeks of smoke when its running like crap?