In gear off throttle "cruise control"
03-06-2014, 07:42 AM
#1
In gear off throttle "cruise control" I am tuning my car and having an issue where when I let off the throttle it wants to keep the idle kind of high...in the 2000 rpm range almost like it is on cruise control. It also does not go into dfco. It will sit at like 12.00:1 afr. It idles just fine when I come to a stop, but until the. It will sit at 1800-2000. Throttle position will be zero but iac is at 130. Then when it drops down it seems fine and everything is normal. I tried adjusting idle airflow down some and it did not seem to change. I will try to post tune and logs.
03-06-2014, 07:58 PM
#2
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Throttle cracker is giving it some "bonus air" when you
are rolling, and it's more than the motor needs. Could be
there is a vacuum leak, or could be that the torque ->
air mass model is just whacked by mods (always the case;
consequences vary in degree).
If your idle, MPH=0 IAC position is very low then this can
be indicating a vacuum leak.
are rolling, and it's more than the motor needs. Could be
there is a vacuum leak, or could be that the torque ->
air mass model is just whacked by mods (always the case;
consequences vary in degree).
If your idle, MPH=0 IAC position is very low then this can
be indicating a vacuum leak.
03-07-2014, 11:22 AM
#5
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Are you seeing a positive pressure before the throttle
blade, at rolling idle / cruise? That is another aspect
that will mess up the predicted IAC-channel air mass
flow vs steps. PCM assumes BARO for figuring out the
IAC pressure difference and airflow value, but that is
no longer true if you're making any boost. If you can
get a reading then maybe some smart guy can figure
out the flow difference and true up that table.
blade, at rolling idle / cruise? That is another aspect
that will mess up the predicted IAC-channel air mass
flow vs steps. PCM assumes BARO for figuring out the
IAC pressure difference and airflow value, but that is
no longer true if you're making any boost. If you can
get a reading then maybe some smart guy can figure
out the flow difference and true up that table.
03-07-2014, 05:15 PM
#7
Would the throttle cracker table make the IACV open? As I said, it is seeing 135 counts when this is happening. I can post a log here in a few.
As for pressure, I would not think it is seeing anything cruising at 2000 rpms and letting off the throttle with as big of a turbo as I have, but I guess anything is possible. Some more background:
5.3
hi-ram 92mm
92mm throttle body Nick Williams
227/233 Lunati cam
4l80e
A2W intercooler
Not sure what else might be relevant?
As for pressure, I would not think it is seeing anything cruising at 2000 rpms and letting off the throttle with as big of a turbo as I have, but I guess anything is possible. Some more background:
5.3
hi-ram 92mm
92mm throttle body Nick Williams
227/233 Lunati cam
4l80e
A2W intercooler
Not sure what else might be relevant?
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03-08-2014, 12:54 PM
#11
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I think cracker is giving you more air than you need, but
the question is why - two hypotheses have been offered,
0, 1, 2 of them could be true.
Cracker only asserts a desired airflow adder, IAC counts
moved to what the PCM thinks will get it there, PCM's
thinking can be confused by realities that are not modeled
right.
I have found that the cracker needs way less air than stock
tables ask, with just a moderate cam and no boost.
the question is why - two hypotheses have been offered,
0, 1, 2 of them could be true.
Cracker only asserts a desired airflow adder, IAC counts
moved to what the PCM thinks will get it there, PCM's
thinking can be confused by realities that are not modeled
right.
I have found that the cracker needs way less air than stock
tables ask, with just a moderate cam and no boost.
03-08-2014, 02:52 PM
#13
Your not logging any of the needed idle pids. Use my idle.cfg file and do a cold start idle scan til operating temp. Don't touch the throttle of move the car while scanning.
Then copy the desired idle airflow histogram (last value)v& paste into your RAF table in your tune (make sure the units match). For the low temp cells you didn't hit, just make them the same difference from stock as the next warmer cell that was hit.
I can't upload my file, just change the extension to .cfg
Russ Kemp
Then copy the desired idle airflow histogram (last value)v& paste into your RAF table in your tune (make sure the units match). For the low temp cells you didn't hit, just make them the same difference from stock as the next warmer cell that was hit.
I can't upload my file, just change the extension to .cfg
Russ Kemp