Stalling issue fixed...I hope... - ZR-1 Net Registry Forums

Paul Workman · 07-10-2017

I hesitated to post this, cuz I'm a little embarrassed. I forgot just a leeeetle step in setting the idle air screw/IAC procedure and it caused me some confusion, frustration, and ultimately caused me to doubt my abilities to walk and chew gum simultaneously! But, then I figured mebby I can help someone else from having the same issues. Here's my story and I'm sticking toit!

Ami's (race-prepped) 91 ZR-1's RPM always seemed to sag and then stall immediately after firing up after the car was sitting over night, i.e., COLD.

If one could catch the sag with a blip of the throttle, the stall was avoided and all was well. But, that was the first indication of things to come.

Then things began to develop: occasionally it would stall after coming to a stop. And, when the summer temps and humidity rose, it would stall every time when coming to a stop - less than 100% only if the AC was not turned on.

The scanner (best tool I ever bought!) told of some issues:

the RIGHT side O2 was sluggish, and the average voltage was on the low side, compared to the LEFT O2. (I replaced that first as the O2s need to be working properly before attempting to do anything else with the idle.)
the TPS voltage was a bit "off".
the IAC counts were mid 80s to 90s. (should be way, way lower. Yikes!!)

The "desired" idle setting was 850 RPM, but actual was 1100. That didn't alarm me, cuz I suspected that was due to whatever might be caused by those other issues. And, it was.

Attempting to lower the IAC steps, by adjusting the TPS idle air screw - , I musta forgotten the instruction regarding setting the idle air screw: cycle the ignition OFF for 10 sec or so before re-starting the motor and reading the IAC counts again. Cycling the ignition between changes in the TPS, and especially the TPS idle air set screw is critical. Otherwise, the IAC counts may change some or not at all if one tries to adjust the idle air screw with the motor running. (Hey! I'll blame it on decades of carburetor experience w/ idle air screws!

At one point I was turning the screw clockwise [to open the primary throttle plate] when idle RPM started running away yet the IAC counts remained unchanged!

) Anyway, cudos to Marc Haibeck, and later reiterated by Dominic for reminding me about cycling the ignition OFF/wait/ON between adjustments: a day and night difference!

______________

I'll save anyone who has done this the eye strain of setting the IAC beyond this point. But, for those interested in setting their IAC/TPS, and have either a scanner or a computer program (Tunerpro or the like), this is what worked best for me...

For those unfamiliar, idle air screw is intended to assure the motor will start and idle in a fashion until the ECM can take over idle chores. Screwing the idle air clockwise opens the throttle plate letting in more air.

The Idle Air Control (IAC) is controlled by the ECM to further regulate the air flow by pulsing (or stepping) the IAC motor: the greater number of "steps", the more air is allowed past the throttle plate. With only the motor running at operating temp, i.e., no lights, fans, AC, etc., the IAC steps should be low, e.g., 5 to 10 depending on the motor's tune and other factors.

The Throttle Position Switch (TPS) is responsible for telling the ECM the position of the throttle plate (opening). Optimally, it should be 0.54 volts when at normal idle. By loosening the two screw at the front of the TPS just enough, the TPS can be rotated to increase or decrease the voltage to achieve the optimum setting of 0.54 volts. (BTW, any changes to the idle air screw will directly affect the TPS voltage. So, changes to the TPS voltage should only be done after the idle air screw has been adjusted - NOT the other way around!)

NOT cycling the ignition between settings (idle air screw in particular and TPS voltage) was an exercise in frustration. Once that was resolved, things went off "easy-pleazy":

Note: The more air let in via the idle air screw, the fewer IAC "steps" will be called for by the ECM. After backing off the lock nut, turning the idle air screw clockwise will ultimately LOWER the IAC steps, and visa-versa.

after warmed up to operating temperature and while motor is running, read IAC steps and TPS voltage for reference.
cycle the ignition OFF.
turn the idle air screw ~ 1/2 turn (CW to lower IAC "steps", CCW to raise IAC "steps").
after the ignition switch has been OFF for at least 10 seconds or so, without starting the motor just yet, turn the ignition to RUN and optimize the TPS voltage to 0.54 volts.
start the motor and read the IAC steps.
turn the ignition OFF. If further idle air screw adjustment is needed, repeat steps 2-6 as often as needed until the IAC steps are within the acceptable range and the TPS voltage is 0.54 volts. Then go onto the next step.
ignition OFF, secure the idle air screw while tightening the jam nut.
start the motor and verify the IAC "steps" and TPS voltages are still correct. test the ECM/IAC function by turning the (AC) on while monitoring the IAC steps. The IAC "steps" should be higher to compensate for the additional load in order to maintain desired RPM. Verify the actual idle RPM is still at of very close to the "desired" RPM setting.

So far, so good.

Actual idle RPM matches the "desired" set RPM value (more or less, allowing for the loping cam idle)
No more sagging and stalling on first startup of the day
No more stalling when coming to a stop or idling in traffic, with or w/o the AC and/or the lights running.
Happy wife...happy life!

Roadster · 07-10-2017

Great write-up, as I will add this and Dominic's write-up to help get me get the engine started when all of my work is complete....

secondchance · 07-10-2017

Glad you got it sorted out.

ssrszz4 · 07-10-2017

What type scanner are you using?

Sent from my XT1585 using ZR-1 Net Registry mobile app

Paul Workman · 07-10-2017

Quote:

Originally Posted by ssrszz4

What type scanner are you using?

Sent from my XT1585 using ZR-1 Net Registry mobile app

I'm using an ancient AutoXray 1000 hand held unit, programmed for OBD-1(that one no longer made, actually.)

There are several software options for laptops and even smart phones with Bluetooth plug-in to the ALDL port.

Ccmano · 07-10-2017

Another gem, thanks Paul.
H

07-10-2017	#1
Paul Workman Join Date: Nov 2007 Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri Posts: 6,493	Stalling issue fixed...I hope... I hesitated to post this, cuz I'm a little embarrassed. I forgot just a leeeetle step in setting the idle air screw/IAC procedure and it caused me some confusion, frustration, and ultimately caused me to doubt my abilities to walk and chew gum simultaneously! But, then I figured mebby I can help someone else from having the same issues. Here's my story and I'm sticking toit! Ami's (race-prepped) 91 ZR-1's RPM always seemed to sag and then stall immediately after firing up after the car was sitting over night, i.e., COLD. If one could catch the sag with a blip of the throttle, the stall was avoided and all was well. But, that was the first indication of things to come. Then things began to develop: occasionally it would stall after coming to a stop. And, when the summer temps and humidity rose, it would stall every time when coming to a stop - less than 100% only if the AC was not turned on. The *scanner* (best tool I ever bought!) told of some issues: the RIGHT side O2 was sluggish, and the average voltage was on the low side, compared to the LEFT O2. (I replaced that first as the O2s need to be working properly before attempting to do anything else with the idle.) the TPS voltage was a bit "off". the IAC counts were mid 80s to 90s. (should be way, way lower. Yikes!!) The "desired" idle setting was 850 RPM, but actual was 1100. That didn't alarm me, cuz I suspected that was due to whatever might be caused by those other issues. And, it was. Attempting to lower the IAC steps, by adjusting the TPS idle air screw - , I musta forgotten the instruction regarding setting the idle air screw: *cycle the ignition OFF for 10 sec or so before re-starting the motor and reading the IAC counts again.* Cycling the ignition between changes in the TPS, and especially the TPS idle air set screw is critical. Otherwise, the IAC counts may change some or not at all if one tries to adjust the idle air screw with the motor running. (Hey! I'll blame it on decades of carburetor experience w/ idle air screws! At one point I was turning the screw clockwise [to open the primary throttle plate] when idle RPM started running away yet the IAC counts remained unchanged!) Anyway, cudos to Marc Haibeck, and later reiterated by Dominic for reminding me about cycling the ignition OFF/wait/ON between adjustments: a day and night difference! ______________ I'll save anyone who has done this the eye strain of setting the IAC beyond this point. But, for those interested in setting their IAC/TPS, and have either a scanner or a computer program (Tunerpro or the like), this is what worked best for me... For those unfamiliar, idle air screw is intended to assure the motor will start and idle in a fashion until the ECM can take over idle chores. Screwing the idle air clockwise opens the throttle plate letting in more air. The Idle Air Control (IAC) is controlled by the ECM to further regulate the air flow by pulsing (or stepping) the IAC motor: the greater number of "steps", the more air is allowed past the throttle plate. With only the motor running at operating temp, i.e., no lights, fans, AC, etc., the IAC steps should be low, e.g., 5 to 10 depending on the motor's tune and other factors. The Throttle Position Switch (TPS) is responsible for telling the ECM the position of the throttle plate (opening). Optimally, it should be 0.54 volts when at normal idle. By loosening the two screw at the front of the TPS just enough, the TPS can be rotated to increase or decrease the voltage to achieve the optimum setting of 0.54 volts. (BTW, any changes to the idle air screw will directly affect the TPS voltage. So, changes to the TPS voltage should only be done after the idle air screw has been adjusted - NOT the other way around!) NOT cycling the ignition between settings (idle air screw in particular and TPS voltage) was an exercise in frustration. Once that was resolved, things went off "easy-pleazy": Note: The more air let in via the idle air screw, the fewer IAC "steps" will be called for by the ECM. After backing off the lock nut, turning the idle air screw clockwise will ultimately LOWER the IAC steps, and visa-versa. after warmed up to operating temperature and while motor is running, read IAC steps and TPS voltage for reference. cycle the ignition OFF. turn the idle air screw ~ 1/2 turn (CW to lower IAC "steps", CCW to raise IAC "steps"). after the ignition switch has been OFF for at least 10 seconds or so, without starting the motor just yet, turn the ignition to RUN and optimize the TPS voltage to 0.54 volts. start the motor and read the IAC steps. turn the ignition OFF. If further idle air screw adjustment is needed, repeat steps 2-6 as often as needed until the IAC steps are within the acceptable range and the TPS voltage is 0.54 volts. Then go onto the next step. ignition OFF, secure the idle air screw while tightening the jam nut. start the motor and verify the IAC "steps" and TPS voltages are still correct. test the ECM/IAC function by turning the (AC) on while monitoring the IAC steps. The IAC "steps" should be higher to compensate for the additional load in order to maintain desired RPM. Verify the actual idle RPM is still at of very close to the "desired" RPM setting. So far, so good. Actual idle RPM matches the "desired" set RPM value (more or less, allowing for the loping cam idle) No more sagging and stalling on first startup of the day No more stalling when coming to a stop or idling in traffic, with or w/o the AC and/or the lights running. *Happy wife...happy life!* __________________ Good carz, good food, good friendz = the best of timez! 90 #1202 "FBI" top end ported & relieved Cam timing by "Pete the Greek" Sans secondaries Chip & dyno tuning by Haibeck Automotive SW headers, X-pipe, MF muffs Former Secretary, ZR-1 Net Registry Last edited by Paul Workman; 07-11-2017 at 09:51 AM.

07-10-2017	#2
Roadster Join Date: Mar 2014 Location: Warrington PA Posts: 1,914	Re: Stalling issue fixed...I hope... Great write-up, as I will add this and Dominic's write-up to help get me get the engine started when all of my work is complete.... __________________ Tom 1994 ZR-1 #009 "captured test fleet car" 1974 LS4 454 Vert 1974 L-82 355 Vert. 1982 L83 CFI...now a retired "dd"....Sold WAZOO Member

07-10-2017	#3
secondchance Join Date: Aug 2006 Location: McLean, VA Posts: 3,721	Re: Stalling issue fixed...I hope... Glad you got it sorted out.

07-10-2017	#4
ssrszz4 Join Date: Jan 2017 Location: US Posts: 233	Re: Stalling issue fixed...I hope... What type scanner are you using? Sent from my XT1585 using ZR-1 Net Registry mobile app

07-10-2017	#6
Ccmano Join Date: Jun 2006 Location: Sparks, NV Posts: 2,852	Re: Stalling issue fixed...I hope... Another gem, thanks Paul. H __________________ 90'ZR-1 #1461 Red/Black Ported Intake, Degreed Cams, OBX Headers & Exhaust, Fidanza FW, Secondary Delete, Custom tune, C6 GS Wheels. Sold 08 C6 Z51 Crystal Red Metallic Sold Vararam Intake, Tune, Sold 05 C6 Z51 Red/Black Sold 90'ZR-1 #1723 Black/Gray Sold but not forgotten 91' Z51 L98 White Vert. My First, you always remember your first. Sold.