What does this do? Is it basically just using the governor actuator to open the throttle?

 

If-in your talking about like on a caddy, it pushes on the throtle linkage to open the blades to add air like an IAC.

 

Throttle kicker for what?.
As mentioned ISC, instead of IAC?.
Antisipated Radiator Fan turn-on?.
P/N gear change.
There probably are others.

Dunno guvenator actorator...

 

If you are talking about the ISC motor there is quite a lot of talk about them a few threads down in this thread: https://www.thirdgen.org/techbb2/sho...hreadid=331767

 

That seems to fit the evidence at hand quite nicely. There is a bit in a CPU hardware addr. that is toggled on and off. It also adjusts the base TPS reading accordingly.

I guess the ISC mustve been an option, or a proposed option, for the throttle body trucks.

 

The ISC is vacuum controlled on some 454 trucks. They still have the typical IAC, but they also have a vacuum control on the driverside front of the TBI.

 

Indeed, it is on the 7.4L and 4.3L manual tranny trucks and is referred to as the "Idle Speed Solenoid". It is just like the old idle speed solenoid on the carbed trucks. HTH

Edit: Sorry, just re-read the quote, it is not vacuum actuated, but rather as I mentioned, an electronic solenoid.

 

That appears to be what it is. It works with the IAC to control the idle. My guess is that it was included on the trucks that where likely to have engine driven accessories that placed a large load on the engine, or some other form of large external drag.

 

Another neat thing I found out from this is that the TPS is scaled to further take advantage of its range. Basically that means that pretty much all the tps values in the hacs floating around are probably wrong. Oh well, its only about a thousand entries to track down and fix, but hey, no biggie.

 

i have one in my spare parts box. i took off my 1995 7.4 L TBI unit.

it is butt ugly!

 

Can you post a pic of it?

 

sure. will take pic tonight i i dont forget. xmas party last night and a bit fuzzy today.

 

Here's a pic of the one on the 90-95 caddy 4.9L SFI motor.

 

And the one on the 93-95 Northstar. Appears to be the same one just with a mounting bracket.

 

not at all like mine? mine is a circular diaphragm(2.5 inch?) with vac line and a throttle stop screw like devise that pushes open the throttle. vac operated. those appear as electro-mechanical.

 

There appear to be two seperate outputs for the 'throttle kicker', which is a 1/0 type of deal, and I think a PWM output for the governor, which is controlled by a PID routine with the final derivative, prop. and integral terms constituting the output. Id still like to see what you have, Ronny. I suspect that may be the governor. From the code side, the governor appears to only be able to activly close the throttle. Maybe somehow the ISC and governor are all combined into one device?

 

governor? so lack of vac or WOT(higher map) allows the plunger to close throttle? is that how a modern governor works?

 

The governor has to be in there somewhere. Maybe the 'ISS' works off of vacuum? Its possible for the governor to work off of vacuum for a period of time off of the vac canister. Maybe looking at it will tell more.

 

None of my documentation shows anything for the ISS other than a solenoid. See the pic below. I think you may have it mixed up with the TCC control output, which on the '95 and later auto (4L60E) trucks is pulse width modulated and is output on the same pin as is the ISS on the manual trucks, pin E10. HTH

EDIT: On the '94 trucks there is only the one output for the TCC on the auto trucks (E10) on the '95 trucks there are two, E10 for the TCC solenoid and E11 for the PWM TCC solenoid. E11 bieng the assosciated second PWM output.

 

In the $0D, the 'governor' is tied to the shift light/non PWM TCC output (pin E10) and is a fully PWM output that is definatly a governor. Full PID engine speed control based off of TPS, MPH, engine speed, etc. with no reference to idle anywhere.

Havnt dug in yet but the 'throtte kicker' is tied to a seperate output. Its an on/off type of deal with what looks like the IAC integral terms and engine idle speed deterimining when to flip the bit. That one is also on a seperate output.

Also present is what appears to be the PWM TCC output, only used when an electronic trans is present. Again, this is also on a seperate output from either of the previous two.

All three output to seperate hardware addresses in the PCM, and presumably to different pins as different outputs.

Im not the hardware expert end of the deal here so Im sort of perplexed. From the software side, its a governor, almost no doubt, but from the schematic above, its the ISS. WTF?

 

I have never seen a governor equipped vehicle nor have I seen any documentation on one other than the hack. Maybe someone else has seen one.

 

Forgot all about this. Good thing I had my moderator hat on and brought all the info in when posting in an old thread on this or it wouldve been lost forever. It was origionally a stupid ebay link.

First the pic...

 

The governor looks like it works just like I thought it would. The throttle bracket is probably spring loaded and doesnt actually open the throttle directly. The motor probably forces the throttle closed against the spring and the rate/position is dependant on the current supplied to the motor.

 

Ronny, It sounds like what you had was the cruise control actuator.

 

The governor is something that only came on the big cargo trucks if I recall. Might it also be safe to assume that the ISS was really only used on the vehicles with a manual trans?

 

Exactly! Now I am curious to see a governor in person. That governor motor looks like the same motor that runs the linear EGR. The ISS on the manual tranny stuff is just a solenoid like used to be on the old carbed engines to "kick" up the idle when the A/C compressor came on. I have one somewhere that I took off an old Holley commander 950 2" TBI. I'll see if I can find it. HTH

 

IIRC, I posted that a while back. My originol question was about the injector pod, injectors, regulator? Different than any other TBI I have seen. The thing to the side is in fact a governor on what looks to be a 454 TBI.

 

The stupid ebay link thing wasnt directed toward you, BTW. Those drive me crazy to no end since they die and the thread becomes meaningless.

Its neat that they have an entirly different casting just for that.

HaulnA$$,

If I remember the linear EGR on my '93 was just a spring loaded pintle with a solenoid coil(?) on the back. At WOT the weak little spring would allow it to blow open and slag from the CC in my clapped out 4.3 would blow into it and lodge it open, causing horrible idle issues. That and the string of bad, leaky CPI injectors always caused problems. Man I hated that truck...

It would be cool to get some pics of the throttle kicker.

 

O.K., I found that solenoid off that Holley TBI. I don't remember if it is exactly like the ones on the 7.4L TBI or not. It has been a while. Here's the pic.

 

Here's the pic of the Linear EGR from my S-10. I'm not using it. Looks kinda similar.

 

Thanks. The throttle kicker there looks alot like the ones on the old q-jets. Is it just a coil inside that pulls the actuator out?

 

There is also one controlled off of vacuum that looks similar to the Idle Load Compensator on an 80s 307 Olds carburetor. Mounts in the same fashion as the electric.

 

Huh... Maybe thats what Ronny was referring to.

 

Oops... Looks like the S/L and governor are on the same output as the 3->2 shift solenoid.

 

And it looks like the TCC is on the same pin as the ISS, as an on/off output. No mystery after all.

 

Huh!, so I guess you can't have a governor on an electronic tranny truck and you can't have a shift light and a governor at the same time on a manual tranny truck. Maybe the governor is used with a non electronic auto tranny truck, the code would seem to support that. Makes sense.
Yeah, like I said, pin E10. Anyway, here is a pic of the solenoid on the Holley TBI. FWIW.

 

Guys, the trucks that would use a governor would have a Non-Computer controlled Allison 4 spd automatic behind them!!!! The 454 motorhomes do not have a governor. The governor is to keep some worker from overreving the truck or going 100 mph with a heavy load. Think of the super low gearing that most dump trucks, U-hauls, School Buses, etc have. Something in the range of 6:1 with NO OD. That makes for an engine that is turning about 3,800 @ 60. IIRC, most trucks are governed at 4,000 rpm which would give you like 63 MPH. If you tried to drive one at 70 it would push the RPMs up to lik 4,600+ and kill an engine very quickly. Any less gear and the truck would not start off up-hill when fully loaded.

 

I'm totally familiar with the reasoning and application of a governor, I just haven't seen one in person so therefore wasn't familiar with the Allison tranny bieng used. That clears it all up. Thanks for the info.

 

As far as all the outputs go, the previous comments give the incorrect impression as to what the outputs are really used for. Ignoring the comments and visiually tracing the code tells what outputs are actually used for what.

 

soory forgot to snap photo. xmas party clouded my mind. overserved.

 

The following link (see bottom of post) is a pic of the part in question 'Idle speed control actuator'. The pic is from my 1994 GM P-30 chassis RV (Southwind Storm) 454 TBI w/4L80E trans.

figured I bring this to folks attention since it's often referred to incorrectly or even unknown by many. For the older TBI engines (454) there is a vacuum can attached to the throttle cable on the drivers side of the TBI.

This vacuum can is the 'Idle speed control actuator' aka as 'Throttle kicker'.

It serves a few purposes...

As for the 'Idle speed control actuator' it was not installed in all models of GM. I believe only in the truck models such as the P-30 chassis. It is the vacuum can on drivers side of TBI attached to throttle cable. It has a vacuum line running to the 'EGR valve control solenoid' which is on the passenger side of the TBI just forward of it attached to a bracket.

See pic of mine for aforementioned items: https://www.dropbox.com/s/ow3nt7k4hf...B1%5D.jpg?dl=0

Idle Speed/Throttle Actuator - Mechanical: Description and Operation

Purpose: The idle speed control actuator system assists the idle air control system in controlling the idle speed, primarily at cold temperatures.

Operation: The idle speed control actuator is a vacuum operated device which opens the throttle slightly (2 to 3 degrees of angle) to increase the cold engine idle speed, to improve the mixing of the air and fuel, and to allow lower warmed up engine idle speeds. The idle speed control actuator is controlled by the EGR valve control solenoid, which is controlled by the power control module. To increase the idle speed, the EGR valve solenoid is turned "OFF," and no vacuum is routed to the idle speed control actuator, allowing it to open the throttle slightly. To decrease the idle speed, the solenoid is turned "ON" and vacuum is routed through the solenoid to the idle speed control actuator, allowing the throttle to fully close.

In conjunction with the idle speed control actuator system, the idle air control continuously monitors and controls the engine idle speed to the desired idle speed. A Tech 1 scan tool will read the control module commands to the idle speed control actuator system.

The throttle actuator provides another function. The larger the TB, the more the bores expand as the engine gets hot. The 92+ 454 equipped truck ran much hotter than the older square body version. And GM had switched to a heated intake instead of the small heater plate, which was much more effective at heating the TB and keeping it warm after the engine was shut off. Well, a larger bore means the throttle plate must be closed more to keep idle speed low. No problem, right? Just reduce minimum air by turning the throttle stop and you're done. But if you do that when the engine's hot, the next day when you go to press on the accelerator while the engine's cold, the throttle plate is stuck. Not so good. The throttle actuator allowed a way to reduce idle speed when hot yet keep the throttle far enough open when the engine was off so a cooling TB wouldn't seize the plate.

The following is the correct OBD-1 code chart for the early 90-95 years: https://www.troublecodes.net/gm/#codesobd1


As for the adjustment of the 'Idle speed control actuator' (Vacuum can) aka throttle kicker...

Idle Speed Control Actuator Adjustment

Procedure: (from manual)

Before adjusting ISC actuator you must first check the minimum idle speed to be within specifications. Refer to SPECIFICATIONS/IDLE SPEED. (ISC actuator must have vacuum applied so that it is not contacting the throttle lever.) See image VIEW A.

Remove vacuum hose on ISC actuator on warm engine.
Adjust ISC actuated idle speed to 1300 +/- 50 rpm. See image VIEW B.
Install vacuum hose.

In the event the vacuum can is leaking and not holding vacuum and you're unable to source another. You'll need to get at the 'Idle adjustment screw' that is covered by GM on the front side of the TBI. Turn it open roughly 1 turn. This will open the throttle blade slightly. The IAC will/should make up the difference.

As for the adjustment of the 'Idle speed control actuator' (Vacuum can) aka throttle kicker...

Idle Speed Control Actuator Adjustment

Procedure: (from manual)

Before adjusting ISC actuator you must first check the minimum idle speed to be within specifications. Refer to SPECIFICATIONS/IDLE SPEED. (ISC actuator must have vacuum applied so that it is not contacting the throttle lever.) See image VIEW A.

Remove vacuum hose on ISC actuator on warm engine.
Adjust ISC actuated idle speed to 1300 +/- 50 rpm. See image VIEW B.
Install vacuum hose.

Prior to doing this you must make certain that the min idle speed is set first



https://www.dropbox.com/s/ow3nt7k4hf4gimd/20180512_232309%5B1%5D.jpg?dl=0

 

Just in case my above Drobbox link does not work it (ISC) is also pictured here: (item #16) https://lt-truck-gmc.7zap.com/en/g15...623891437-0-0/

Part number:

GM 17084953

 

I am so glad I found this post! DOnt suppose you have the images from the manual so I can carry out this procedure? I have a problem with engine stalling after revving on my RV I have checked and changed everything else, but didn't know the procedure for setup. I wasn't even aware of the idle adjustment screw .

 

I would like to purchase this item from you if it will hold a vacuum mine leaks and I for some reason can't find one or a part number if this holds a vacuum and you would sell it I can be reached at deansplaceny@gmail.com thank you in advance