Stumbling idle when hot, IQ adaptation value over 32768?

2003 Jetta Wagon. 470000km. vnt17, malone 4+, colt cam, race 520 nozzles, egr delete.

Started to get a stumbling idle when the engine was hot. Read up a bit on it, saw the source could be related to IQ or fuel delivery.
No bubbles in clear line from fuel filter seems to disprove any fuel supply problem.

Checked measuring blocks for idle IQ and was showing from 0.2 to 0.0mg/str, and fuel consumption at 0.00
Logged in, checked adaptation for IQ and the value showed 32770!
Changed to 32760 and the idle stumble disappeared. IQ shows 1.0 to 1.2 in measuring window, mod.piston displacement 1.500 to 1.520v (varies)

Should have taken screenshots but didnt think of it at the time.

My questions:
When I read up on IQ and what that number should say, i've been seeing values like 3.0, 4.0, etc - it seems to run and idle fine with it showing 1.0 to 1.2, am I missing something?
Also, I thought the max value for that adaptation field was 32768, why on earth could/would it be set higher?

IQ should be set between 3 and 5 or the car won't run optimally, anything below 2.4 or so usually gives issues. Best to use the hammer mod, and adaptation should remain close to the 32768 preset. It can be adjusted for minor corrections but should be set to the stock value.

http://www.myturbodiesel.com/wiki/injection-quantity-adjustment-fuel-pump-hammer-mod/

Ditto what Owain said, your stumbling because your IQ is too low. You probably need to perform the "hammer mod" and check with VCDS until it gets to 3-5 with 32768 as the value.

Great, that makes a lot of sense. Thanks very much!

The general rule is to increase the IQ (decreases fueling) if the engine wants to stumble when dropping off the accelerator. What the number ends up being is, for the most part, immaterial; what matters is what makes it run properly.

I have two identically modded cars. One I just bumped the IQ to about 6 to eliminate a slow-down shudder.. The other is around 3.

That car has various mods so the IQ value at idle might not match stock numbers.

Example, *maybe* IQ at idle is supposed to be 3 or 4 for a stock car set up correctly, idling at normal ambient air temperature (is it 70F in Canada now?) and with all accessories off.

However in my case I have nozzles on the car that are non-stock so my IQ value at idle needs to be 5.8 in order for the car to have approximately the correct fuel/air ratio over the rest of the range.

It is a crude hack but it is what many people including myself have done. The biggest thing that I noticed after installing new nozzles is that the response off idle was a bit off and I stalled the car a bunch (manual transmission) before I got used to it.

If you want to do things perfectly, the engine computer would need new tables to match the modifications done to the fueling system. In other words a "tune". If the tune is set correctly then it may make sense that the idle IQ would come in 'correct'. You also need to consider the age of the car may be throwing things off.

I was told the tune was done for the mods on the car, but that was before I got it - so I guess I cant know for sure. Can someone with a Malone tool check how the tune is set up? Or is it basically gibberish unless you really know what your looking at? The fuel mileage seems good, (over 40mpg, 25/75 city/highway) better than my last TDI anyway - but there are a few things that are slightly different.

It seems to take longer for the revs to return to idle when you let off the pedal than it should, and it always puffs a bit of white (not blue) smoke on startup (even when hot).

Maybe i'll try just changing the adaptation values to try and get it down to 3-4, and see how it runs - if its terrible I could just reverse it.

Timing on idle is right where it should be, between the middle and top line, so its not getting skewed by that at least.
Idle stabilization is only +/- 0.25 when warmed up as well

32770 is a pretty insignificant alteration; it's almost like someone was trying to deal with the slow-down shudder and gave up. Adaptation isn't for making big IQ changes.

Set IQ Adaptation back to stock and then hammer mod to set. Best guess is that you're going to have to be at least 5-ish, for starters.

Look on the Malone site for information on performance logging. Do as they instruct there and you should be able to tell how things are performing.

I would suggest, however, taking a look at Group 013, injector deviation. It gives an idea on the health of each cylinder's performance.

Keep in mind that air filters and fuel filters can have an impact on performance. If you don't know the state of these then you might consider replacing. Low-hanging fruit is the MAF: logging should identify if this is OK or not.

I didnt know Malone was so helpful! I'm not new to diesels or tuned vehicles in general but this is my first tuned TDI, so i'm learning a ton.

I did look at group 13 as I was flipping through the channels just to see what everything was, and if I remember right the readings (when the engine was hot) were 0, -0.25, 0, -0.25. But I will check that again when I have the chance.

Already have a new air filter and fuel filter, just waiting for the weather to not be horrible to put them in. Planning to run a can of diesel purge through as well, again delayed by weather.

If that's the true numbers for Group 013 then you should be golden: generally if they're pretty well grouped you don't have a compression issue or, generally, injector problems.

Pretty sure that new filters and a bump of the IQ and you'll be looking good.