Why can't I fix my idle problem?

[sdhager]

I am tuning for the first time. I got a base file from wait4me, and the car seems to run OK and idles OK but surges or bucks at light loads. The idle surges sometimes after a throttle change, and will surge excessively and sometimes die after shifting gears setting still. It is a 98 Firebird with a GM Hot cam. I tried messing with RAFIG, RAFPN, but when I set the air flow in p/n to get a zero RAFPN, it won't idle in p/n but is OK in gear. When it does idle OK in p/n RAFPN is abour -2.35 gms/second.

Also, the desired idle warmed up is 750 in gear and 800 in pn, but the car idles about 100 rpm higher than that according to the scanner data, and IAC counts are not changing to fix it. I was under the impression that idle speed was controlled by IAC and timing. What do I have to log to verify what my problem is?

How can I fix these idle swings?

So many questions.

[WeathermanShawn]

I would just suggest as a minimum to check the following:

1. Your AFR (usually too rich if it stalls..too lean will just stumble and then die). VE Tables will address a lot of startup fueling problems.

2. If just starting, just try increasing your desired airflow 1-2 g/s. Works 90% of the time.

3). Set your base spark to 22-26 degrees.

4). Go through all the idle under/over speed parameters.

That will be a good start to solve your problem.

[sdhager]

I hate to be the guy that says "check out the idle tutorials", but there are so many factors involved that unless you address them separately, it can be very frustrating.

I did check out the tutorials. I don't have a time constraint on this one, and I am using it as a learning experience as well. I am not looking for a silver bullet, but a direction, or better yet an accurate theory discussion would be great.

I would just suggest as a minimum to check the following:

1. Your AFR (usually too rich if it stalls..too lean will just stumble and then die..Note: very generalized descriptions..VE Tables will address a lot of startup fueling problems.

This is not a startup problem. This car idles great in park and in gear. It is a transition problem. It only happens when you change the throttle or gear shifter. It happens when you jab the throttle, or sometimes when you shift between drive and reverse or to park and back to drive that the surging starts. It is running in closed loop with near zero fuel trims.


2. If just starting, just try increasing your desired airflow 1-2 g/s. Works 90% of the time.


I logged my RAFPN and RAFIG, and lowering the airflow in gear brought it close to zero, but when I subtract 2g/s from the p/n setting, it won't even idle in p/n. So I set it back, and I now have about -2.36 gm/s for RAFPN when fully warmed up.

3). Set your base spark to 22-26 degrees.

I'll check on that and get back to you.

4). Go through all the idle under/over speed parameters.

Can you be more specific please? I tried some settings that made sense to me, then changed them back.

5). Worst case, try some of the other tunes posted for your year and mods.

I guess I can peruse something close to see how they did it. Maybe it will help. Thanks. Hadn't thought of that.

This is the best 'cheat-sheet' I can give you, but it is probably not a very responsible response to give you. Learning this is not measured in minutes or even hours.


A cheat sheet is good to get you where you want to go, but I want to know the theory behind it as well. I am a professional mechanic, but totally new to tuning. I am of the mindset that I not only want to know how to fix it, but tell me how it works, and I can tell you how to fix it.


But, I hope this is at least a start for you.

Thanks for your help. I appreciate any details you can give.

Good luck.

..WeathermanShawn..

Thanks Again

[WeathermanShawn]

Are you are referring to RAFPN? What other mods do you have?

If idle is good, then when you are changing to another gear you are changing spark parameters from base in gear (or park or neutral) to your high octane spark table. The overspeed/underspeed parameters I was referring to B5935 and B5936 entries.

So many questions, so little time.

I agree on this board as many others, the more generalized the question and the less details (tune & log) given the harder it is to get a good response. If you read SSpdDmon's Idle Tutorial it covers many of the idle/transition problems.

In my M6, the problem was solved by accurate fueling and spark. Spark in base gear was fine, but when I shifted to reverse or in gear, (and I went from open-loop fueling to closed-loop), the drop from base spark in gear to high-octane was too great. Hence, it stalled. Good luck.

[sdhager]

Yea, I knew I was going to 'get in trouble' (joke), by overly generalizing.

I apologize if I have missed some of the obvious, but maybe we are missing some details.

I take it you are are auto, since you are referring to RAFPN? What other mods do you have?

My hunch is if idle is good, then when you are changing to another gear you are changing spark parameters from base in gear (or park or neutral) to your high octane spark table.

With the overspeed/underspeed parameters I was referring to B5935 and B5936 entries.

With the 'cheat-sheet' I was only trying to help you, since your comment suggested time was the issue.

So many questions, so little time.

I agree on this board as many others, the more generalized the question and the less details (tune & log) given, very few will even attempt to walk you through the process.

Hey, I read SSpdDmon Idle Tutorial at least two dozen times before I even posted. (it covers idle/transition problems)

Not trying to be an unhelpful, but perhaps someone else can more easily identify your exact problem.

On my M6, I solved the problem by fueling and spark. My spark was in base gear was fine, but when I shifted to reverse or in gear, (and I went from open-loop fueling to closed-loop), the drop from base spark in gear to high-octane was too great. Hence, it stalled.

Thats the best I can do. Hope you take my comments as just helpful advice.

Good luck.

..WeathermanShawn..

I am going to attempt to load my tune and my idle log when the car is dying. I've not done this before, so I hope it works. The log is setting still with a/c off. Shifting from park to drive and back again. You can see the gear position. Also I can slightly brake torque it, and when letting off fast, the car dies, or surges and dies. When letting off slow, idle is good. I would really like to know what to look for and what to adjust. What I would really like to know is why.

Thanks.

[WeathermanShawn]

Your tune and log posted just fine. I see exactly where it is stalling. I loaded up a stock 98LS1 Auto and your tune is quite different.

I started from scratch (stock). I left as many parameters as possible stock. Did AutoVE, every Idle Tutorial parameter, then developed my own spark tables. My hunch would be that it is choking from not enough airflow. I noticed your Throttle Cracker Table is essentially zeroed out, but if that is even related to your problem I do not know.

Will it run if you just load up a stock file?

[sdhager]

Wow!

Easiest way of saying this, is I do not know. I guess after 6 months of tuning my own car, I thought I might be able to help. Far more complicated when looking at someone else's tune. Especially (for me) an automatic.

Your tune and log posted just fine. I see exactly where it is stalling. I loaded up a stock 98LS1 Auto and your tune is so different, I can only provide what I did.

I started from scratch (stock). I left as many parameters as possible stock. Did AutoVE, every Idle Tutorial parameter, then developed my own spark tables.

Maybe a real expert can help you out here. My hunch would be that it is choking from not enough airflow. I noticed your Throttle Cracker Table is essentially zeroed out, but if that is even related to your problem I do not know.

I apologize for being no help. I would ask again either on this forum or others if you so desire.

I feel your pain. Will it run if you just load up a stock file?

Good luck.

..WeathermanShawn..

Nope. Runs terrible with a stock file.

[mr.prick]

sometimes a full paste and add with RAFIG can be too much.
try cutting the logged values in half.

[sdhager]

sometimes a full paste and add with RAFIG can be too much.
try cutting the logged values in half.

So, are you saying that a RAFIG and RAFPN of zero is NOT desirable?

I have heard to just increase the desired airflow, but is that not designed to bring RAF** in line?

[mr.prick]

RAFIG how to