Idle tuning

[Alvin]

One thing to check before starting idle tuning is that the stop is secure and tight.

I can't tell you how many times I've started on a car, had a rough time, and found that the idle set screw was loose to where you can turn it by hand. Lately I've been putting a dab of locktight on all the NW90's set screws just for my personal sanity.

[Frost]

One thing to check before starting idle tuning is that the stop is secure and tight.

I can't tell you how many times I've started on a car, had a rough time, and found that the idle set screw was loose to where you can turn it by hand. Lately I've been putting a dab of locktight on all the NW90's set screws just for my personal sanity.

+1 The first 90/90 I tuned had a NW90 and it freed itself from loctite even! Can I get a long set-screw and a jam-nut here please?

[WS6FirebirdTA00]

Hmmm, I have yet to have that issue out of those TB but its good to know so I can keep an eye on it

[robfrey]

This is my first posting and I am new to the forum. This is my first experience with tuning any factory ecu. I have a lot of experience with both FAST and Electromotive.
We are having a bear of a time trying to get a twin supercharged (prochargers) Cadillac CTS-V (427 ci) to idle without surging. How much do the above mentioned tips cross over to the "drive by wire" system that is on this Cadillac.

Thanks
Rob
onebadpontiac.com

[EC_Tune]

Idle fueling may cause the surge that you are experiencing. If you are in Closed Loop I would use the scanner to artificially raise and lower the idle RPM and adjust fueling accordingly. It's amazing how just a small fueling change can improve the idle if you have "steps" in the VE/MAF table.

[12secSS]

Idle fueling may cause the surge that you are experiencing. If you are in Closed Loop I would use the scanner to artificially raise and lower the idle RPM and adjust fueling accordingly. It's amazing how just a small fueling change can improve the idle if you have "steps" in the VE/MAF table.

That is the biggest under statement of the year. Most of the idle issues I have seen from previously attempted tuned cams, comes from instable fueling issues. More so then timing related. Good advice Doug!

[colamotas]

That is the biggest under statement of the year. Most of the idle issues I have seen from previously attempted tuned cams, comes from instable fueling issues. More so then timing related. Good advice Doug!

So how can you lean or enrich the idel, just change the ve in the respective cells that the scanner hits in the histograhm?
If so then what % should you start with?

[chpmnsws6]

So how can you lean or enrich the idel, just change the ve in the respective cells that the scanner hits in the histograhm?
If so then what % should you start with?

Bumping this up

Do you change the idle VE table while you are in RTT?

My car idle surges badly when rolling upto the stoplight, but once at the light, it idles fine (on a 1999 C5 with a 224/230 cam)

[EC_Tune]

Probably need a bit more base running airflow.

[John_D.]

One thing I found recently, is when my idle would start oscillating, is there is a lag between the map changes and the wb readings due to the slower exhaust flow at idle.

The rpms would drop, the map would go up, I would move into a higher VE %, which was actually making the fueling richer, but would appear lean on the wideband.

Then the rpms would increase, the map would go down, I would move into a lower VE, which was actually making the fueling leaner, but would appear rich on the wideband.

So my AFR histogram would suggest dropping the VE even lower at low kpa, and would suggest increasing the VE at higher kpa values, which just made the problem worse.

Once I figured out that the rise and fall of the WB AFR wasn't really exactly mapping the rise and fall of the MAP kpa, then I was able to stop falling into that trap. There was more like a phase shift between the two lines (in the chart view) and they were actually going in opposite directions instead of tracking each other. Once the time lag was considered.

It was going lean at the low map / higher rpm because the VE was too low there. My map was ranging from 50 to 60 kpa at idle. (sometimes 70 if it got really bad) After I pulled the lower range of the idle VE (50kpa) back closer to the higher map range (60kpa) it tamed most of the oscillation in the idle.

Because of the time lag in the wb reading at idle, the histogram was telling me to do just the opposite of what needed to be done.

(it's more pronounced on mine because I have the wb in the tailpipe after the rear mount turbo...)

[chpmnsws6]

Seemed to have fixed that. Now I'm trying to deal with "off idle" power being very weak. I really have to rev it up to get off a stop light or you'll kill it, but on the highway, it will not buck or anything till you get under 1200rpm

[blued turboed1]

My Issue is when I put the car in gear it idles up. Also when slowing to a stop it dosent idle down. Takes about 30 sec anyway. The cruse control thing I guess.

[louvered97gtp]

Subscribed. Awesome thread. this helped me realize the potential use with the VCM controls. Great help guys.

[LosLS2]

Only thing I will add for idle tuning is to turn OFF the LTIT. No point in having "learning" moving things around while you are tuning.
These are the values you need to adjust:
Attachment 4688 Attachment 4690
Attachment 4689 Attachment 4691

Do you just leave these settings or do you put them back after your done tuning?

How are LTITs calculated?

[truckmann]

Put them back after your done getting the idle airflow.

[LosLS2]

Put them back after your done getting the idle airflow.

OK. Still would like to know how LTIT and STIT is calculated by the PCM. What sensors are used?

[WS6FirebirdTA00]

I believe it is based on idle air control and where it is in relation to keeping and idle and where it is commanded to be without the STIT/LTIT control.

[EC_Tune]

^^^ Correct. The STIT is the equivelent of STFT in fueling and LTIT is the equivelent of LTFT in fueling.

They are calulated off the base running air flow table. It is an adjustment +/- to that base airflow. The STIT & LTIT add together to offset the base running airflow to keep the engine idling properly.

[Gh0st]

Anyone have tips to make the car not dip down to 600rpm when making a hard turn while idling? All other idle is perfectly fine.

Car will also dip when slipping the clutch, even died three times for the guy backing my car up at the shop lol

[LosLS2]

^^^ Correct. The STIT is the equivelent of STFT in fueling and LTIT is the equivelent of LTFT in fueling.

They are calulated off the base running air flow table. It is an adjustment +/- to that base airflow. The STIT & LTIT add together to offset the base running airflow to keep the engine idling properly.

The reason that I asked this is that I created a STIT+LTIT PID in order to correctly setup RAF. No matter what, it always reads a negative value. I mean I can get it down into the 6's and the car is barely running and it still wants me to pull air. I was thinking the maybe the MAF had something to do with getting the values correct and since I dont have one, hence the erroneous data.

Any suggestions? Another way perhaps?