RPM's dip slightly when moving 1-2MPH in Neutral, Why?
 

Let me try to explain.

I start my car in the garage and pull it out, I let it sit running for a few minutes so it can warm up to normal temp. My driveway has a slight slope to it, so after it's warmed up, I release the Ebrake (M6 car). When I start moving like say 1-2 MPH with car still in neutral, I am "coasting" down my driveway to my road (about 15 -20 feet) the RPM's will dip slightly by about 100 rpm or so then go back to a nice smooth idle. I have checked the IAC to see if it is closing when the car starts moving and it's not, the IAC postion stays the same, about 60 at idle, but it will go up when you give it gas, which is normal.

I have tried adjusting the idle air table, throttle follower decay (lowered 70%), throttle cracker (raised 5%). Most people probably wouldn't even notice and just accept it as normal, but it's my new quest to get it running close to stock. My cam is not that big 226 222 116lsa.

What table do I adjust to correct for this dip in RPM? It's gotta be MPH related since it only does it when moving. Other than that, the car runs like stock, let off the gas when out cruising and the rpms come down nice and easy to idle with no surging what so ever, but every once in a while while crusing, it might dip 100 below set idle speed when you push the clutch in while moving.

Evertime I think I have it fixed with a new upload, after 20+ miles or so and a cold start, it goes back to doing it again.

What tables control this? Throttle Cracker? If it is the Throttle Cracker Tables, what direction should I move the values, lower or higher, and by how much?

Any help would be appreaciated.

Bill

There is a setting for max idle mph (something like that). Bacically the PCM will consider the car idling if it's under that speed. I bumped mine up a bit to fix a similar problem. It sounds like the PCM does something different once you start moving, thinking it isn't idling anymore.

Where is this setting in either LS1 Edit or HP Tuners?

Don't know. I use EFI Live. FWIW it's on the parameters table under Idle using their program.

Could you show me the table you used (post it on here) and I'll compare it to LS1 Edit & HP Tuners.

Thanks......... ;)

Parameters Value
{B0107} Max Speed for Idle Mode 12.000000 MPH
{B0108} Max Throttle for Idle Mode 0.507813 %
{B4401} Default IAC Motor Park Position 310.000000 steps
{B4402} Maximum IAC Steps 365.000000 steps
{B4311} Throttle Cracker enable speed 2.000000 MPH
{B4312} Throttle Cracker disable speed 1.000000 MPH
{B4321} Throttle Follower TPS change 0.996094 %
{B4501} Idle Learn Enable Temp 176.000000 °F
{B4502} Idle Learn Disable Temp 233.585938 °F
{B4322} Idle Learn P/N Limit High 0.000000 Grams/Second
{B4323} Idle Learn P/N Limit Low 0.000000 Grams/Second
{B4331} Idle Learn P/N A/C On Limit High 0.000000 Grams/Second
{B4330} Idle Learn P/N A/C On Limit Low 0.000000 Grams/Second
{B4324} Idle Learn Drive Limit High 0.500000 Grams/Second
{B4325} Idle Learn Drive Limit Low -3.000000 Grams/Second
{B4329} Idle Learn Drive A/C On Limit High 0.500000 Grams/Second
{B4328} Idle Learn Drive A/C On Limit Low 0.000000 Grams/Second
{B4301} Fan #1 IAC Correction 0.150391 Grams/Second
{B4302} Fan #2 IAC Correction 0.370117 Grams/Second
{B4601} Max Idle RPM in Gear 1200.000000 RPM
{B4602} Max Idle RPM in P/N 0.000000 RPM

Which one did you change?

The first one. "Max Speed for Idle Mode." That parameter and "Max Throttle for Idle Mode" determine when the PCM thinks it's idling.

I changed it to 12mph. It seemed that every time I rolled into my driveway in neutral and turned the wheel, the engine rpm would drop. That combined with some f'ed up values in the idle spark correction tables would make the engine stall. I changed a bunch of parameters to get it to stop.

what was the stock value?

The stock value was 0mph. 12mph is probably too high for most, but it fits my driving style.

thats a good tid bit of information to know, i would think 5 mph would be ok for most or a good place to start