ldo_marlin

I am helping a friend tune a GM TBI setup on an International motor. The ECM is a '7747 $42. Everything works fine except sometimes the motors likes to idle high between gear shifts (manual trans) or coasting to stop. For instance, taking your foot of the gas pedal, the vehicle wants to continue on because rpm does not come down quick enough. Coasting to a stop the RPM will be at 1500 until vehicle comes to a stop then the RPM will slowly drop down to idle RPM.

I've played with the IAC setting and even backing off the IAC min. count to 5 and does not seem to help. IAC has also been changed out to a new unit. Throttle body is a 454 unit from a 94 Chevy truck.

I have the same set up in a older Suburban with manual trans and don't have this problem. The only difference is i don't use a VSS .

Any ideas?

90c350

Do you have the vss setting turned off?? It also sounds like you may have a bit of a vacume leak. When the iac was replaced did you guys clean out the throttle body passages?? Or you may have the min idle set screw turned up to far. Just a few thoughts, not sure it this will help you??

ldo_marlin

No vacumm leak. New throttle body so passages are clean. Pretty sure the min idle screw is set correctly.

Previously, I tried disabling the VSS function in the bin but it did not help. I'll have my friend disconnect the speedo cable to the VSS to see if it changes anything.

Other ideas?

Thanks -

90c350

Any idea what the blm/int values are?? Maybe its a little to rich/lean at that rpm. OR you need to look at the DFCO values and see what they are set at. Just thought's though.

ldo_marlin

blm/int are pretty close to 128.

DFCO enable speed 18
DFCO disable speed 15
DFCO enable rpm 1400
DFCO disable rpm 1000
DFCO enable map 13.3 kpa
DFCO disable map 34 kpa
exit DFCO fuel pulse width 7.08 msec
exit DFCO fuel pulse width delay 400 msec
DFCO Max % TPS 1.6%TPS
DFCO enable Coolant temp 56C

What an easy way to disable DFCO? May be setting DFCO coolant temp to a really high value so that it's never enabled?

Brandon2350

Is this combo original to the vehicle? Programming for a standard trans and auto trans are different.