Another TDI with Missing/Lumpy Idle


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Feb 11, 2012
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Hi all.

My A3 TDI 140 has recently started to play up on idle. I've done some searching and there seems to be various answers to other peoples queries ranging from the DMF to simply 'a common problem that can't be diagnosed without throwing £££'s at it'.

However, I thought if maybe I put my symptoms someone can help...

When the car is at idle the whole car/engine seems to shake a fair bit and almost seems like it's miss firing or something, but it's notiocable to the point you can physically see and feel the shake. I think it was initially worse once the car had warmed up but now seems to do it when the car is less warm...although not so much on initial start up. It's a bit sporadic with when it does it, sometimes it'll be on every time the engine ticks over, sometimes it'll go a few ticks fine then sometimes a few ticks jumpy etc etc

The symptoms don't seem to change regardless of whether the car is in gear, clutch in, out of gear or any combination of just stays the same regardless. I had a friend at VW who got it plugged in for me and it did come up with a 'cam sensor' issue having previosuly been logged, but the engine light is no longer on for this?!

The symptoms DO disappear once driving or even just revving the engine just over idle, it's literally when the car is idling.

Also, not sure if this is linked but recently it also seems to be a little less keen to start once the car is warm. When cold it'll start up right away but once warmed up it takes a good few seconds for it to finally turn over?!

One final thing, it does have some 'plug n play' chip fitted that was done prior to me owning the car...could this be a culprit as I know these aren't overly recommended?

I'm away at the moment so can't get to a garage but also I don't want to fall into this catagory of people who seem to be throwing money at similar problems but not coming to a solution, so thought I'd give it a shot on here to maybe get an idea of what it may be and likely to cost.

Cheers all and any advice appreciated.
Sounds like the Plug and play.

I have had the same on mine; it too has a plug and play and does make it perform so much better.

What you need to do is find the adjusting screw on the kit, wind it in slowly til the engine runs rough, then back off the screw three whole turns. This should solve the problem.

It looks like the previous owner has had it wound in too far and is not far off the rough running segment I mentioned before winding it out.

Any problems PM me and I will see if I can talk you through the adjustment.

Oh and the engine light normally comes on when the plug and play kits are not tuned correctly.
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I do hope the problem is something as simple as this!!

I think I'll do it all properly at some point soon and get a remap anyway, so have been considering removing the current unit completely. I'll be honest, I've never even looked at the unit properly and only seen the cable that runs into the ECU box (or at least that's what I'm assuming is in there - I'm not at all mechanically minded :laugh:)...are these usually as simply as just unplugging the thing or can the removal differ depending on brand etc?
Ok, so I've managed to get someone to check for me today and apparently there is no adjusting screw?! It's actually a TDI-Tuning box that's been fitted.

Could this still be causing the issues and would it be worth removing completely, or is this now more likely to be something different altogether?
Check CAM timings using vcds - mine was quite bad and is now fine after some adjustment!!
Warm start is a problem normally associated with the starter motor or battery. Mine is still bad!
It's actually a TDI-Tuning box that's been fitted.

Is this the one that just plugs in the fuel temp sender?

If so we had a 1.9 TDi in work today that had a lumpy idle, a quick checked with VCDS had a fault for fuel temp sender logged, but hadnt put on the MIL

Had a quick look on the wiring, and the original bit of loom with the 2-Pin plug that used to go on the fuel temp sender had snapped off, probably where it is left with the loom for the tuning box hanging on it. So shortened loom, fitted new plug and all was well.

Then had a bit of a heated debate with the customer about these tuning boxes, I was trying to explain that it can only be making it dump in extra fuel as the only bit it connects to is the fuel temp sender, but he was adamant it could talk to the ECU from that single 2-pin plug and change the boost.... ended up prooving him totally wrong by showing the reading from the fuel temp sender in VCDS, without tuning box fuel temp was 40degC, with tuning box plugged in it instantly changed to 120degC.
I think it is one that just plugs in as you said and tricks the car into pumping in more fuel?!

I'll be removing it when I'm back home I think, checking the wiring and see if there are any changes.
Same problem, only happens/noticeable when stationary.

Started on its own, but as time had progressed it's almost defininatey dual mass issues for me.

Just hope that when I do get it done in a few weeks (if it lasts) the wobbles goes as well!!

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