Idle Surge Problem

[MTCFORUM]

I need to fix a bad idle surge I have, but I need a little help with the best or right way to do it. I've heard of several different things to do, like; disconnecting the IAC and using the stop screw, adjusting the bypass screw, drilling holes in the throttle plate, changing injector slopes, adjusting the lower part of the MAF transfer, etc, etc. It's a 93 Bird, P3M with an EEC-Tuner. I don't have my WB finished yet, so I don't know my A/F. My suspicion is it's running lean, I got a red spot on the top of the passenger-side cat after about 20 minutes of idle from a cold start. Here's the symptoms: On a cold start, idle surges up to 1500 or so RPM and will die if I don't keep working the gas, holding it @ 2000. Once it warms up a little, it will hold an idle, but goes in and out of slight surging. If I 'blip' the throttle, the engine will die when it decelerates. If I let off the gas slow (down to idle), then I can keep it running. What is the correct order of steps to solve this problem?

By the way, although this is my first post, I've been hanging around here a few weeks now. Great BBS! (Thanks Todd!)

[MTCFORUM]

You know you may just not be getting enough idle air. So the EEC tries to compensate by holding the IAC wide open, then it goes way too high, so it backs it way too far down, so this makes the surge. When I added cams to my engine, I had this issue. All that needed to be done was to add more idle air, if it is like an EEC-V there should be 2 functions, one for park/neutral idle air, and one for drive idle/air. This is what the drilling the throttle plate would accomplish, I'd rather do it in the EEC. Don't ever change to incorrect injector slopes, lying to the EEC is bad, as always.

[MTCFORUM]

Thanks Kris...

This did start happening with the new engine, it has a pretty aggressive blower cam. There are no idle air setting tags that I can adjust (I'm using the Shiftmaster software) so here is what I was going to try, (someone please tell me if this is incorrect or not). I don't want to drill the throttle plate unless ABSOLUTELY necessary ;-)

1) Open the bypass screw as far as I can
2) Disconnect the IAC connector
3) Adjust the set screw until I get the idle RPM I want
4) Reset the TPS voltage
5) Set the Drive and Idle RPM's in the tuner to match

Any flaws in my thinking here? Thanks for any help...

[MTCFORUM]

Well I agree with what Kris suggested you do. Let me tell you what's going on.

The idle speed control is not as closed loop control as you think. Air responds way to slow to be aggressive with it.

There are two functions in the EEC that have desired RPM on the X axis and air in #/min to get that rpm on the Y axis. One for park, one for drive. When you start the car, or even run it at idle. It calculates the desired RPM, then looks up the amount of air to get this in this function. It then takes this amount of air to another table that is coolant temp vrs #/min of air flow. The output of this table is the duty cycle for the ISC valve. It then puts the ISC valve to this duty cycle. Now, if you changed cams your air requirements are no longer correct. You start the car, it gets a duty cycle that's now too low, based on the cam, and the RPM is too low. It goes into a stall protect mode, if the RPM drops low enough, or uses an integrator to add air in based with the ISC valve. The issue is this is a slow system. At the same time, it is using spark to trim the idle speed to get it close to desired RPM. So, the RPM is too low, it over corrects, goes too high, and gets you into this "do loop".

You need to fix this in the EEC.

The things you are doing may help, but there other side effects that happen.

jerry

[MTCFORUM]

Thank you for the detailed explanation Jerry...and so goes the dilemma, I don't think I have the tags available to me to adjust those functions in the P3M .eec file. I don't have the binary dump with me here at work, but I believe the only table I have that references air flow is the MAF transfer function. Will re-mapping the MAF transfer function at the idle voltage help? I know that lying to the EEC is bad, but if I have no other choice...then lie I must.

Any thoughts, opinions or options here? I'm open to doing a re-pin and swapping out the P3M for an A9L, A9P, or something with a little more support (and datalogging) <IMG NAME="icon" SRC="http://images.zeroforum.com/smile/emwink.gif" BORDER="0">

[MTCFORUM]

Where are you located at?

jerry

[MTCFORUM]

Jerry, I'm in Chicago...western suburbs.

[MTCFORUM]

Jeff,

You should take a trip to St. Louis on the weekend of April 27-28th for this <A HREF="http://mtcforum.zeroforum.com/zerothread?id=163" TARGET="_blank">http://mtcforum.zeroforum.com/zerothread?id=163</a>

[MTCFORUM]

Thanks, I saw that post...unfortunately I'm scheduled to move in the beginning of May, the better half won't let me do car stuff until we're done <IMG NAME="icon" SRC="http://images.zeroforum.com/smile/emsad.gif" BORDER="0">

Our dyno tune plans kinda fell apart here...so I'll need to wait for the next one or maybe a road trip to Michigan

[MTCFORUM]

You're dead on about issues with the tune. If we could just gather 8-10 solid spots it would be simple. No one was able to commit except two of us. I think we'll eventually jump on the badwagon with another tuning session. That or we drive up to MI. Not like we're really ready yet anyway like Blown306 posted.