Idle (transition) tuning procedure for C5's (drive by wire).

A collaborative effort between Nick Williams and myself. A lot of testing on many cars has been done to ensure the process works. Besides it makes sense. There are pieces of information that have been stated by others, but seem to have been somewhat ignored. The MAPS in EFI have helped make the tuning process easier. We are very open to ideas,or the need for clarity. You can prove the process by logging the information suggested, from a stock car and you will see the results make sense.

The following assumes a reasonable tune has been done to the car. Here is a quick outline of my preferred method.
-Put back all stock airflow and timing values.
-Input the stock IFR values for stock injectors, or calculate new values for larger ones.
-Put in A/F multiplier values(PE RPM), calculated to your preference. (ex.14.7/12.8 = 1.15 mult.)
-Work on VE's with the MAF zeroed. (You can do speed density. I just don't feel it's worthwhile if you run an MAF. JMO. Others can do what's right for them.) Bring the MAF back on line and adjust it for ltrims.
-Then do Idle Transition Tuning.

Idle transition tuning:
-Start with Ltrims reasonably negative and your Standing Idle is set where you are happy with it at all temps.
-If your VE's are off by 20% or more they need to be set.
-Return all airflow tables to stock, except idle, idle airflow parked(IAC Park) and idle airflow(RAF). This is so the car will idle. If you can return all the airflow tables to stock, go ahead.
-Set up Maps for Maf gms/s and Desiac gms/s, by ECT. Use the format in the PCM.
-Log, IATc, ECTc, SAE MAF gms/s, GM DESIAC gms/s.
Since you are in open loop when you first start the car, watch for your trims to show(closed loop) and your idle to settle to where it's set and start the tuning log.
Log while parked, from the coldest engine temperature to fully warmed.
Log for at least five minutes after warm up to get better averages and since this is the temperarture where problems are noticed.
-If it's an a4, log in gear with the A/C on. You may want to repeat this process in neutral later or just check to see if your RPM's stay up when driving and you put the car in neutral.
-If it's an M6 log in neutral.
-Input the logged MAF values into the idle airflow (raf) table, by temperature.
-Raise or lower idle airflow parked (IAC park ) values.
You want to match logged desiac and maf values.
This is done within each IAT range. You will need to watch Desiac and Maf results in Dash f10.
Raising/lowering IAP raises/lowers desiac.

The idle airflow parked table is the difficult part for a number of reasons.
-The temperatures are IAT. Some think they are ECT.
-The temperature scale is in 20c increments.
-Raising the IAP values raises logged desiac, and raises expected airflow. The TB closes some and you could get stalling surging, etc., if your target is wrong. The opposite scenerio would be racing. This is important, since you are working with logged averages and may/probably need to make small adjustments and the affect is counter intuitive.
-This need to be done on different days in order to set within each IAT range as weather changes push your intake temperatures up or down.

-Finally, timing will help idle and flare at start up. If you have EFI Pro you
can use BI-D Controls to test(SOP)timing changes, otherwise program
timing changes a little at a time. Make the changes in Base Spark in
Gear and Base Spark in Park/Neutral.
-Check, ltrims, AFR and adjust.
-When you change IFR's, MAF #'s, timing and airflow table values, the
trims are affected

This process will help eliminate, stalling, surging, false idle learn and unlearn, colds, headaches, etc. My opinion is that many of the problems that occur after a cam are a result of not understanding the IAP table. You will notice that your ltrims and strims become flatter.

There are some situations that make perfection a little harder.(Maybe impossible). Don't have knowledge past a G5X3.
-Really big cam. ex. Mine is a 228/589/112 in an a4 and tuning is easy.
-Long tubes that place the 02 sensors far back, which allow them to cool fast and take longer to heat up.
-Cold air intake, which causes rapid IAT changes.
-Any throttle body with a ridge that's been worked.*
-Descreened MAF/ not properly calibrated.
-Low rear gears(3.73 and lower) and a stock or almost stock stall converter.
-The tuners ability.


* I continually read opinions that the 90mm TB is hard to tune. The N. Williams 90mm TB and stock TB's are not hard to tune. It's the cam.

Don't look for perfection in the numbers, they do bounce around. If after you do this it idles and transitions well, be happy.

 

This should be a sticky!!

I don't understand why there hasn't been much response?This was posted over 7 hrs. ago?


Guys, the airflow values set from these tables effects your Tune globally.
If these are right, along with the VE as gojo states, most of the surging, bucking and hanging are eliminated.

This is as "cookbook" as you can get.

Thanks gojo and Nick!!

 

i think it was posted on hptuners.com a few weeks back as well...definitly should be made a sticky IMHO very good info for the dbw guys.

 

Hey Joel, Nick is a very sharp young man. I wish he would make TB's for the f-body guys. Thanks for the TTT.

 

What is dashF10

What is IAP

-Raise or lower idle airflow parked (IAC park ) values.
You want to match logged desiac and maf values.
This is done within each IAT range. You will need to watch Desiac and Maf results in Dash f10.
Raising/lowering IAP raises/lowers desiac

 

"What is IAP"

IAC Parked airflow is what he meant.

 

Dash f10 is in EFILive - so I doubt this was on HP Tuners site .

 

Closer, I use EFI so I probably have HPT's terminology wrong. Hopefully we will get HPT users helping. I cross referenced Edit above. I am familiar with it.

With EFI V7, Maps(pivot tables?) can be created. Dash F10 references which dash to watch in EFI. With other scanners just watch your logging or export to Excel.


BTW, I've had a couple of emails and the reply addresses were rejected.

 

Here it is.

 

You can also try using the new idle MPIDs we added in 1.6.0 i think they will remove a lot of steps from the process Imho, they are much more useful for tuning than the spark PIDs everyone is making a lot of noise about during the "who's catching up to who" threads

Not to mention VCM Editor now includes just about *every* idle parameter in the PCM, and the help file has some info there too.

Long Term and Short Term Idle trims are where the action is, and also boundary checking the adaptive limits removes any mystery about idle transitions.

New Idle Airflow MPIDs (vehicle dependant):
- Startup Airflow
- Throttle Cracker Airflow
- Throttle Follower Airflow
- Fans Airflow
- Startup Retard Airflow
- AC Airflow
- Base In Gear Airflow
- Long Term Idle Trim Airflow In Gear
- Base PN Airflow
- Long Term Idle Trim Airflow PN
- Short Term Idle Trim Airflow
- Park Position Airflow

 

Any info on exactly what changes should/should not be made on the adaptive idle limits?

 

Agree'd, HPT seems to be one of the most comprehensive publicly available tuning tools available, and still has marginal information available. The website is a great help, and if nothing else, a support group. But an indepth write up on the parameters abilities would make a lot of these questions null. Venting. Sorry, wore my search button out already.

 

Best Info I have found so far!!

I was actually going in that exact direction

 

the help file contains the info however here's what you can do.

Monitor your two LTIT's and STIT in the scanner. You will notice the LTIT should settle to a constant value after a few minutes (idle learn process) in PN and Gear for A4's and Gear for M6's. After the LTITs have settled take note of the following:

- the LTITs should be within the min/max limits shown in the editor (see the help file)
- the STIT should be close to 0

If the LTIT's are at either the min or max limit you have a problem with your base running airflow (if LTIT is max and the STIT is positive then your base running airflow is too low, if LTIT is min and the STIT is negative base running airflow is too high). Also it's good to watch your STIT when the fans come on so you can see if the correction is ok.

I tend to keep the limits at the factory settings and just change the base running airflow numbers and the various compensation factors.

The important thing to remember is the base running airflow is the starting point for the adpative idle routines. Most cruise control and rpm drop issues when coming to a stop are symptoms of the LTITs being at their limits due to base running airflow being out to much. This is most noticeable after a camshaft change.

Chris...

 

Various compensation factors?? Can we elaborate a little?

 

I believe he is talking about the Decay in PN & Gear, Delay in PN & Gear, Throttle Follower and Cracker, IAC vs. Effective Area and all those "other" tables in the one little screen.

Chris, thats a bunch for that quick tech tip.

Charlie

 

The main one is the "Cooling Fan Airflow" this is the extra IAC airflow required to compensate for the alternator load when either one or both fans are on.

There is also the throttle cracker which opens the IAC based on RPM and mph, and the throttle follower which is a dampener/decay function for when you close the throttle suddenly.

The other is the AC. The AC is a little different as it is torque based, you'll need to head over to the Engine -> Torque Management -> Engine Torque section and look at the "AC Compressor Torque" tables. Again, watching your LTIT and STIT when the AC comes on will tell you which way you need to move things.

Chris...

 

OK, so what the heck does the IAP table do. How does it impact the IAC. I understand that RAF is the base and the other do some minor modification, but how does IAP come into play. The old school info was that IAP was just used during cranking.

Also, why do the FANS require a correction. More load on the alternator should not impact fueling, right? I can see some voltage issues, but that is what injector offset is all about, right? AC makes sense, but electric fans don't.

Maybe this will all be well understood some day.

 

The IAC airflows play no part in fueling calculations at all.

The PCM uses "airflow" as it's means of opening the IAC stepper (or ETC). It has no relation at all to fueling calculations at all.

The fan correction is used to provide a more seamless idle RPM transition for the increased alternator load. Rather than just wait for the adaptive idle routines to move. The AC is the same, it only controls the IAC and nothing to do with fueling.

 

Yea, I really stated that wrong. I should have asked why turning the electric fans on would require the IAC stepper to open wider (which results in more load/fuel). I might be missing something, but I don't understand how the alternator would become harder to turn because the fans are on. It would make sense if you had a fan clutch that was being driven by the belts, but I thought the alternator was just a constant load. AC makes total sense though. I must be missing something basic.

Also, do you think the IAP has impact on the IAC position while the motor is running? There seems to be no clear answer on that one. Some seem to be seeing some results from changing it.