Huge idle problem...

[mulot30th]

Used RTT to try just about every combination of low timing, high timing, this car keeps stalling each time I go from park to reverse or drive...

On this tune I have idle setted at 1100 rpm hot, because its the only way to avoid stalling just about everywhere, and even then its not very good... A/C will stall it if I don't give it gaz.

Its been 6 years now this car had heads/cam, and never had a good idle, never.

Cam is :230/230 .578/.578 with 112 lsa so its not a very big cam and I can't imagine it should idle any more than like 800-900 rpm steady. I have ported stock TB.

With idle at 950 rpm and 22deg of timing, got iac to like 35-38, with timing at 30 degrees, IAC goes to 8-10. So it seems to react correctly to timing at least.

Need help please Attachment 7182

[Russ K]

Is your car supercharged? By setting your maf fail freq to 0 and then setting P0103 to no error reported, your maf is in control of the fueling. There has to be a maf code for the car to be in SD mode. A large cam likes more idle spark, and your in drive spark table is stock at idle, and the in park table is only 2* more than stock. And your main spark tables are way too high. Your LTFT's are disabled, this should be enabled and the map & rpm boundaries need to be set up for your camshaft. Do you have an idle scan log showing the idle pids? Then the RAF table can be set up.

The trans tables need a lot of work.

Russ Kemp

[mulot30th]

No MAF, its pure SD tune, I use 2 bar, but the 1nd bar is for dry nitrous only.

Notice the voltage on the MAP sensor is all divided by 2 because I still have the stock 1 bar sensor with a voltage divider to make the pcm think its a 2 bar. I say that just in case you want to try this in you car!!!

Car was a 6spd and is converter to a manual body automatic tranny, so I don't use tranny tables.

I do not have stock o2 sensors anymore, so this is why no ltft/ stft

I don't get any ping on this timing table, I can even add a few more and still no knock.

It runs to perfection everywhere EXCEPT idle... then its all crap!

[mulot30th]

Okay, I just made a quick log of idle
Using rtt I progressively set it from 1100 till 750 for you to see what happens

Then I shifted her in reverse and it immediately stalled.

Attachment 7185

Attachment 7186

[Russ K]

That scan doesn't have the right pids for idle tuning. Use my idle cfg file & do a cold start scan in park till operating temp without touching the gas or moving the car. Then do the same with the trans in gear. Then paste the desired airflow histogram into the matching p/n & gear rows of the RAF table.

Looks like your idle afr is very rich, I would enable closed loop.

Russ Kemp

[mulot30th]

closed loop will be very hard to do since I have no more 02 senrors for like 2 year on that car... only widebands for logging.

All I can do is to adjust fueling accordingly which is not very complicated.

I will log this tomorrow since I need to let the car cool down.

[mulot30th]

That scan doesn't have the right pids for idle tuning. Use my idle cfg file & do a cold start scan in park till operating temp without touching the gas or moving the car. Then do the same with the trans in gear. Then paste the desired airflow histogram into the matching p/n & gear rows of the RAF table.

Looks like your idle afr is very rich, I would enable closed loop.

Russ Kemp

I just loaded that file and just dont see nothing on the scanner's table display...

[mulot30th]

Do you want this:
-Spark advance (was logged)
-TPS (was logged)
-IAC steps (was logged)
-Idle desired airflow (not logged)
-Dynamic airflow with SD (only cylinder air flow was logged)
-LTIT (in gear for manual and autos need to log both gear and p/n) (no 02 so can't do it)
-STIT (no 02 so can't do it)
-Wideband or fuel trims (LTFT/STFT both banks) if you dont have a wideband (was logged)
-MAP (was logged)
-RPM (was logged)
-ECT (was logged)
-IAT (was not logged)


so was missing the IAT and idle desired air flow and dynamic airflow right?

[VYSSLS1]

Car was a 6spd and is converter to a manual body automatic tranny, so I don't use tranny tables.

there is your problem,

you PCM does not know when it is in park or gear, so it cant adjust the idle air flow for the differences,

you will have to try upping the timing at the lower air flow areas and adjust the VE table until it will idle in gear

[mulot30th]

there is your problem,

you PCM does not know when it is in park or gear, so it cant adjust the idle air flow for the differences,

you will have to try upping the timing at the lower air flow areas and adjust the VE table until it will idle in gear

But even not in gear, idle will just stall as well if I turn on A/C.... almost everytime... so I will log now

[mulot30th]

I logged from a cold startup till operating temperature using all idle parameters I could (only O2 missing)

Again, programmed to progressively go from 1100 till 750 at operating temperature as you will see.

As soon as I shifted into reverse, she stalled.

Attachment 7191

Attachment 7192

[mulot30th]

Byt the way, not 750 rpm but 850 rpm!!!

Here is another one using RTT I leaner her, but still doing exact same thing!

[mulot30th]

Attachment 7194

[mulot30th]

Okay got it to idle no too bad at 950 rpm with A/C on and in drive... so this is good news.

Afr is oscillating between 14.7 and 15.2
Timing is oscillating in the 36-42deg area
MAP is at 7.8X psi... if I add a few more timing deg, it start to surge.

Only problem is when I come to a stop too quickly, rpm dip way low (like 400 rpm) and struggle to get back to 950rpm. Same thing if I turn on/off the A/C... but funniest thing is its worse when I turn A/C off.


One last thing, after each tune flash, it have a real hard time to get correct idle at startup (like 300-400 rpm for 20-30 seconds and then suddenly get up to 950 and hold there) and it will do it ONLY first start after a flash.


Do you have any pointers for me?

[Cybnext]

The car is learning the STITs on the first startup, which is causing the hard time starting.

I believe if you get your RAF table correct, it should start much easier.

[mulot30th]

Does it use O2 sensors to learn stlt?


because I don't have them anymore.

[SSUte01]

I think you may be confusing Fuel Trims with Idle Trims ie STFTs (fuel trims based on O2 closed loop) and idle trims (STITs based on a host of variables namely the difference between desired idle airflow and calculated idle airflow but importantly not based on the O2s).

After much dicking around with various cars and learning the hard way on my own, the best thing you can do is get the fuelling (VE or MAF or both, I see you're SD) right where you want it and then use a good idle config (much like RussK's or make your own) to get the desired idle airflow to be similar to the dynamic airflow which will be close to the RAF.

Fuelling has a large impact on the STITs and therefore the RAF - for shits and giggles open your bi directional controls and lean out the idle AFR manually and watch the STITs (and eventually the LTITs) go much more positive or at least must 'bigger', likewise richen the fuel up and the STIT will decrease or become more negative.

Point is, once you have a car that runs use a good idle cfg file (there are shitloads around, use the sticky or make one up yourself -lemme know if wanna hand as I think the knowing the Scanner is more important than knowing the Editor) so use the scanner from cold to get a good reliable RAF dialled in, remember that changes to fuelling will affect this, so sort VE first. Once the RAF is happy and STITs are alwys within earshot (ie +/-0.25 to 0.50 g/sec) then you will remove the dipping issues the start up issues, the flaring issues etc - unforutunately it took me far too long to figure this out.

The final thing to consider when trying to set up a good SD idle is make sure your IAT is reliable as this will also affect your fuelling (agian look at the BIAS tuning threads etc)

The key IMO to most idle issues (outside mechanical limits if massive cams etc) is having an accurate RAF (ie close to zero STITs) I chased my tail for many months blaming one thing or another on my issues and now finally my car is very consistent (touch wood) and I really enjoy driving it in traffic, hot, cold etc. The problem is the adaptive idle isn't fast enough to react to dipping and/or flaring so therefore the RAF must be close and reliable.

These are just my findings and what has helped my issues in the past.

Hope you get it sorted

[mulot30th]

At risk of sounding really stupid... that RAF you talk about, is it the Base running airflow in the editor?


Also... My desired idle airflow is almost always about HALF of the Dynamic airflow in the scanner... I guess this is real wrong...

What table have a direct impact on the dynamic airflow (at idle) so I can make it match the desired airflow?

thank you

[SSUte01]

At risk of sounding really stupid... that RAF you talk about, is it the Base running airflow in the editor?


Also... My desired idle airflow is almost always about HALF of the Dynamic airflow in the scanner... I guess this is real wrong...

What table have a direct impact on the dynamic airflow (at idle) so I can make it match the desired airflow?

thank you

Sorry, I hate acronyms for this very reason, yes RAF is Running Airflow or Base Running Airflow.

Nope not necessarily real wrong, defining right or wrong IMO in this context is whether it works or not.

I have played for hundreds of hours just with idle changes on several cars, std cammed, mild cammed etc to see what does what.

These are my conclusions, still dunno if they are 'right' but they work for me. I have never drilled a TB, but have come to the conclusion that it is necessary on some setups. I currently have my TPS idle voltage at 0.63V, which means my final airflow at operating temp is ~5 g/sec or a bit more than half like yours. So I have effectively opened the blade which is no different to drilling the blade, in fact I firmly believe you are better off keeping idle voltage stock and drilling as idle voltage affects other areas.

Without digressing, I can set my TPS voltage to 0.53V and this will make desired airflow, dynamic airflow and RAF (therefore STITs close to zero) the same and it is very well behaved at idle, problem is when its cold it starts like crap and stumbles and is a real PITA, why not up airflow setting etc? because the IAC was maxxed, this is a mechanical limit, no tuning in the world could help me, so back to 0.63V (I just dont wanna put a hole through my TB yet) and now IAC is not maxxed (upper end though, as you'd expect for cold start) and idle never dips, surges etc, at worst it may hang a tiny bit to 1000rpm (idle is 900 as M6), which I deliberately setup with cracker settings, zero them and it stays ~900.

Try creating a histogram or use the cfg file below (bear in mind it has a lot of things in it, that you dont need for this particular task, it is my generic idle cfg I use for narrow down issues) and log Idle Desired Airflow against ECT and insert those values into the RAF table in the Editor. This will get you a good start point and then use STIT vs ECT to make the fine tuning.


A few gotchas though are ensure bonnet up to minimise heatsoak, like I said above this will skew your data considerably and get idle fuelling where you want it prior to setting this up.

This will mean your RAF will be a lot lower than stock, but if it works, it works, it seems to me you can set the RAF (keeping STITs zero) at any amount if you fiddle around, and I dont think there is a right or wrong approach.

What were your STITs anyways, if they were like -3g/sec the issues you describe will occur.

Hope this is of some help to you as nothing more frustrating than idle issues IMO.

[mulot30th]

You file just does nothing into my wcmscanner... as does any of the cfg files I downloaded lately... Do you use custom PIDS?

But I decided to include Idle Adapt (stit) and LTIT gear/Acoff pids into my own cfg.