Audi B6 Help/Advice Needed - Cold Start/Flat Spots/Boost

[stevekoz]

I've got a b6 Audi A4 with the 2.5 v6 TDi 180 bhp Quattro.

The car was mapped prior to my ownership - not sure by whom as don't have any paperwork and didn't really discuss it much with previous owner.

The car has a couple of niggly issues currently i am looking for some help with.

1. Cold Start Issue

The car has a cold start issue.

During the summer months this wasn't an issue at all so its definitely temperature related.

On first turn of the key in low temperatures the car struggles to turn over. She won't fire immediately and once she does she is lumpy for 2/3 seconds feels like she'll cut out and lets out a puff of white diesel smoke. She never smokes on running or any other time. Its only on first start up. Its def white smoke and smells of diesel.

This ONLY happens the first time she is started. If i turn her straight off and then restart she catches and starts perfectly and will start and run perfectly the entire day thereafter. It only ever happens first time of starting. Starter motor was tested not long back and was cycling proper voltage.

I have changed the coolant temperature sensor as i thought this might be the issue but no luck. I'm stuck next as to what it might be.

Anyone suffered similar issues? Glow Plugs? what else could it be??

2. Flat spots

The car is remapped. By whom i don't know. I don't have paperwork and it was prior to my ownership. However, the car suffers from two flat spots at 2000 and 3000 rpm. Normally you don't really notice them that much so the fault appears intermittent. I think this could be boost related as sometimes she feels hesitant under boost, like the power is there but is struggling a little bit to come through.

I have played with the actuator and it moves fairly freely. There is no black smoke. The seals look good on the turbo and it doesn't always happen. Could this be down to a faulty N75 valve and is there a way of testing this/bypassing it to see if this could be the issue. My thoughts are it is failing to cope with the increased boost all the time due to having been remapped.

Therefore is there a replacement/performance variant N75 valve that would be suitable for the car - would fitting one from a later 3.0 tdi make a difference for example (if you can even do this?) and if so where can i pick up such a part other than Audi/VAG i can't seem to find them for sale anywhere.

If not that could it be MAF? What else might cause such flat spots?

3. EML/EGR

The EGR valve throws up an EML code. I've blanked off the EGR (disconnect and blocked vac line as per instruction) and it runs now without limp mode kicking in but its constantly got the EML light. I wonder. If the car registers that EML could it retard the timing a little bit or cause any of the above problems (boost issues/flat spots) due to the fact its retarding timing a little as it registers there a code that would normally limp mode the car? Hasn't gone into limp since disconnecting the EGR.

I'd really appreciate some comments and help and ideas as i'm a bit lost.

I've just spent £1000 on her due to a crank pulley failing and any more issues i just can't really stomach so toying with selling her rather than fixing her but if these issues are simple fixes then i may be tempted to keep going with her a wee bit longer.

Cheers all.