LT1 High Idle

[ReidB]

Just so we know, none of the parts places manufacture parts- very likely the part you buy in an oreilly box is the same you buy in a Napa box, etc.

Further, are you sure you're not getting only 77% of mechanical travel in your linkage? Have an assistant push the accelerator pedal to the floor. Then try to manually move the linkage at the engine. Any additional motion bears investigation (floor mats, poor linkage design, etc).

I only key in on this because you did say it was a transplant.

True, none of the parts are manufactured by the parts stores. But the part I bought was from China and would not sweep voltage in line with the specifications. I read 0.48V with plates closed, 3.0V at WOT. From what I could find, specs calls for approx. 0.5V at idle, 4.8V at WOT. Oreilly was cool with upgrading to a BWD unit. (Which hopefully isn't coming off the same production line.)

Good point on the linkage. I am sure of WOT because I swept the throttle shaft by hand under the hood with laptop on the dash. 100% needs to happen with the throttle blades fully open. Once the TPS sweeps correctly the pedal can be checked with the laptop.

[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

[ReidB]

OK quick update... Installed a new TPS, BWD unit, US made, worked great. Disconnected all interconnections between the ECM and TCM. Fired right up, sounded pretty good, idle will only go down to 1200-1300rpm with IAC closed. It looks like the air hole between the throttle plates was probably drilled larger than stock.
The right O2 is intermittantly dropping to 0. Something not right there.
I had turned off the MAF enable flag. Turned flag back on, went to flash, got an EEhack error "Select T side or select E side to flash". Both are greyed out. Don't know what to do....
Forcing closed loop mellows out the idle, but runs rich. Hopefully the O2 issue.
Not sure how to get the truck puter to share signals without screwing up the engine puter signals. Has anyone done this successfully? I'm thinking a voltage follower buffer chip might keep the two isolated. Gonna need more beer to get thru this:)
I've attached my last eehack log file.

Thanks all!

[steveo]

when both options are greyed out, that means your 'compare' bin is identical to the bin you are trying to flash.

[ReidB]

when both options are greyed out, that means your 'compare' bin is identical to the bin you are trying to flash.

Thanks Steveo. I thought I had toggled a flag or two. Will give it another try.

[ReidB]

Another question...
Is there a way to reset the IAC pintle depth? Mine is staying open at 0 counts. Enough to maintain 1600 idle. Cover the IAC port and idle comes right down.

[91ss]

Sounds like it might be time for a new one.

[bentrod]

for 93 lt1, TECH 1 or equivalent tool can manually control. Probably applies for your year too. Though if counts at 0 and you're idling at 1600rpm, sounds like something else is wrong like vacuum leak or tuned too lean (e.g. injector values incorrectly set).

Maybe check IAC pintle seat for obstructions/jams? Also all intake related gaskets good and hoses/blockoffs in good shape? You can spray starter fluid to listen to rpm change sometimes.

[ReidB]

for 93 lt1, TECH 1 or equivalent tool can manually control. Probably applies for your year too. Though if counts at 0 and you're idling at 1600rpm, sounds like something else is wrong like vacuum leak or tuned too lean (e.g. injector values incorrectly set).

Maybe check IAC pintle seat for obstructions/jams? Also all intake related gaskets good and hoses/blockoffs in good shape? You can spray starter fluid to listen to rpm change sometimes.

Thanks guys. I checked for vacuum leaks with carb cleaner, hard to get good feel with the high rpm. Pumped intake full of smoke (finally a good use for a year old cigar) no leaks. Replaced IAC, reset pcm, fired up and rpm came right down.

[steveo]

that's good,

now what are your IAC count at hot idle?

[ReidB]

that's good,

now what are your IAC count at hot idle?

Didn't let it run up to hot but running 4-8 counts at 560-600rpm, 150deg F. Hasn't been down the road yet. Sounds good but smells rich. Showing AFR 14.2, O2s 448/457, injectors 3.1. Need to get off the blocks to blow out the cobwebs.

[ReidB]

Still have dead oil press, temp, fuel gauges. Strange, seems like they are all hardwired but the circuitry on the cluster disappears into a black hole. Totally confused. Seems like it should be either hardwired or data bus, not some of both.
I did try a buffer chip to isolate the signals between the 2 pcms. Seems to work good, the tach works now, no more floating voltages.

[ReidB]

Sounds like it might be time for a new one.

You're 2 for 2!