LT1 High Idle

[steveo]

the IAC is jacked wide open but you're above target idle, probably because your tps needs to be 0% at idle (it isn't trying to control idle at all), your TPS is 1.6%. close your throttle blades all of the way so they're almost stuck in the bore.

this may be due to a wiring fault or interference, , meaning TPS voltage may be unstable?

the LT1 ecm usually finds 0% tps by minimum voltage without issues, so unhook the battery for a bit to reset the ECM memory. then start it while giving it no throttle. it should self-calibrate.

Anyone know how to check the iac? It ohms out ok but it would be nice to be able to power it open and closed and check the plunger depth vs the bore depth.

yes, eehack 'control' section, check idle 'steps', then idle 'override', you can move the pintle that way.

[ReidB]

the IAC is jacked wide open but you're above target idle, probably because your tps needs to be 0% at idle (it isn't trying to control idle at all), your TPS is 1.6%. close your throttle blades all of the way so they're almost stuck in the bore.

this may be due to a wiring fault or interference, , meaning TPS voltage may be unstable?

the LT1 ecm usually finds 0% tps by minimum voltage without issues, so unhook the battery for a bit to reset the ECM memory. then start it while giving it no throttle. it should self-calibrate.



yes, eehack 'control' section, check idle 'steps', then idle 'override', you can move the pintle that way.

Makes sense that it doesn't want to idle with the 1.5% tps. The blades close fully. They held carb cleaner on benchtop.
Graphing tps voltage is awesome. Didn't know it could. Multimeter swept 0.56 to 3v. Seems like it should hit 5v at wot.
Stupid easy is what I need.Great program/tool.

[ReidB]

the IAC is jacked wide open but you're above target idle, probably because your tps needs to be 0% at idle (it isn't trying to control idle at all), your TPS is 1.6%. close your throttle blades all of the way so they're almost stuck in the bore.

this may be due to a wiring fault or interference, , meaning TPS voltage may be unstable?

the LT1 ecm usually finds 0% tps by minimum voltage without issues, so unhook the battery for a bit to reset the ECM memory. then start it while giving it no throttle. it should self-calibrate.



yes, eehack 'control' section, check idle 'steps', then idle 'override', you can move the pintle that way.

I'll have to separate the control wiring from plug wires like 91ss suggested.
Need to reset tps and see if i can get it to settle down. I couldn't get pintle to control before i found vacuum leak.
Found out hard way do not share coolant temp signal with anything. It shares ground with iat and tps. Causes voltages to float freely.
Thanks for input! Have some troubleshooting to do.

[steveo]

you need to be careful about grounding sensors in a custom harness. when something connects to an ecm directly for its ground, you need to use that as your ground, as they're specially filtered for noise. don't ground anything else to them or you might fry the ecm from the load, and don't splice those and ground them to chassis.

this definitely could be your problem.

[ReidB]

you need to be careful about grounding sensors in a custom harness. when something connects to an ecm directly for its ground, you need to use that as your ground, as they're specially filtered for noise. don't ground anything else to them or you might fry the ecm from the load, and don't splice those and ground them to chassis.

this definitely could be your problem.

My harness is definitely a work in progess. I haven't directly (or purposely) grounded any dedicated grounds or left any bolted grounds to float. I'm retaining the truck's PCM as a TCM to control the electronic trans functions because it includes the programming for 4 low and PWM TCC lockup (Its a 95 4L60E). The engine is running 'stand-alone' on the 94 LT1 PCM/ECM.

This all sounded pretty straightforward, but sharing signals has added another level of complexity. From what I have read, the TCM needs signals from the TPS, CTS, VSS, and tach to operate. With splicing wiring between the TCM and ECM, I found that the CTS signal cannot be directly shared (at least not with my setup). It is factory wired to share the ground with the TPS (wiring diagram below) It also seems to internally share a ground with the IAT. I had floating IAT and TPS signals until I cut the splice which fed the CTS signal to the TCM. It seems I may need a third temp sensor for the trans.

Something similar could still be jacking with the ECM functions. I'll follow up as I get further.
ECM Wiring_7.jpg