Drive by cable absolute throttle position % at idle

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Original poster
Member
Jul 21, 2020
55
Miami
Hope everyone is doing great.

Please clear up some confusion I have related to my LM7 which is a drive by cable throttle body. I have a throttle position sensor (TPS) and an idle control valve (IAC) on my throttle body. I have confirmed after cleaning the IAC and the hole it installs into on the throttle body (disconnected the battery for 30+ min) that with my Torque Pro app that my IAC is providing the correct range of “counts” moves at the appropriate times and settles in around 38 to 40 at idle.

So here is the question. Should the absolute throttle position read 0% at idle? Mine reads sometimes 0.39 and others 0.0. Sometimes at idle it even fluctuates between the two. There is a correct range to 100% at WOT. With KOEO, it reads 0.0%. Then most of the time, when the engine is started, it goes to 0.39%. Funny thing is, with the 0.39 readings, I get random misfires in most of my cylinders. (No misfires other than at idle) Not many just 2 to 4 per cycle. If I put the A/C on to induce a load, the throttle position stays at 0.39, RPMs stay at 550, pulse width increases and the misfires seem to go away.

Is the ECM seeing the 0.39 and it’s associated voltage and thinking more air is entering the system than is really being supplied? Fuel trims (short and long) are below 5 on both banks and MAF reads a steady 4.8 g/s. If 0.39 is not what it should be reading at idle on a drive by cable throttle body than maybe that is a good place to start given the additional load test. Please confirm so I do not go off chasing a dead end.

Thanks.
 

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
Chances are it is a service (mode) 01 standard pid for throttle position(s). The usual equation for these is A/255*100. Work this out for a returned value of 1 yields 39.215686275.
 

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Original poster
Member
Jul 21, 2020
55
Miami
The PID is built in. It is called “throttle position (manifold)[11]. When I run the range KOEO, it goes from zero to 100 when I slowly depress the gas peddle . It says a units on the display “%”. Not sure how to verify the PID on these built in PIDS.
 

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Original poster
Member
Jul 21, 2020
55
Miami
I tested a PID 221143 from a list from the web which is described as being “throttle position sensor” which returns a A value with KOEO of 28.0. As I depress the pedal slowly, it raises to around 200. That is the only thing I am moving. Could that be voltage? The TPS is supposed to transmit back to the PCM a factor of voltage of min 0.0 to 5.0 volts
 

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Original poster
Member
Jul 21, 2020
55
Miami
If I test PID 220011 I get an A value KOEO of 1.0. So that would follow. I will test the range of PID using that equation with the KOEO. And also with the KOER. Be right back
 

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
The PID is built in. It is called “throttle position (manifold)[11]. When I run the range KOEO, it goes from zero to 100 when I slowly depress the gas peddle . It says a units on the display “%”. Not sure how to verify the PID on these built in PIDS.


That is service 01, pid 11(hex). You can read about it and others here.


Scroll down to "service 01" and you will find pid hex 11 listed at the left column.
 

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Original poster
Member
Jul 21, 2020
55
Miami
Excellent page. Great info. So the only way for the equation to equal the minimum value of 0.0 is for A to return a zero. I do not remember ever seeing A as zero before. Have you ever seen that? Are there other Torque users who monitor this built in PID with drive by cable throttle bodies?

As tested with both your equation and the one from the table (should have listened to my middle school math teacher about the rules of multiplication and division) lol, A=1.0 KOEO travels to 100.0 slow pressing of the gas pedal and then returns to 0.39. KOER, A starts at 0.39 and travels to 17.5 at 3000 rpms under no load and then back to 0.39. Did not see 0.0 tonight but I have seen it at idle after driving on the highway and coming to a stop. So I guess an A value of zero does exist.

Is your LM7 a drive by wire or cable?
 

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
Excellent page. Great info. So the only way for the equation to equal the minimum value of 0.0 is for A to return a zero. I do not remember ever seeing A as zero before. Have you ever seen that? Are there other Torque users who monitor this built in PID with drive by cable throttle bodies?

As tested with both your equation and the one from the table (should have listened to my middle school math teacher about the rules of multiplication and division) lol, A=1.0 KOEO travels to 100.0 slow pressing of the gas pedal and then returns to 0.39. KOER, A starts at 0.39 and travels to 17.5 at 3000 rpms under no load and then back to 0.39. Did not see 0.0 tonight but I have seen it at idle after driving on the highway and coming to a stop. So I guess an A value of zero does exist.

Is your LM7 a drive by wire or cable?

Mine is fully drive by wire.
 

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Original poster
Member
Jul 21, 2020
55
Miami
Ok. Hopefully there is some other members who have the drive by cable throttle who can shed some light on this. Thanks again for your continued insight.

Any thoughts on what the 221143 PID could be expressing?
 

mrrsm

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Oct 22, 2015
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Because the Early LS Engines employ an analog or MECHANICAL Air Intake Control Mechanisms and yet must still communicate information to the PCM in a simplistic manner, it employs the following Positional Controlling Devices:

(1) The Mechanically ADJUSTABLE Throttle Position Sensor:

This adjustment variable is VERY SLIGHT in Rotation and can become a REAL PITA to get right if you should start fiddling around with it. If you must replace a Failed TPS in the Throttle Body... Try to set the position of the New One Dead Center in the Adjustment Slot before GENTLY tightening down the Two TPS Fasteners.

Unlike the PID Adjustments necessary for the FULLY Electronic Throttle Bodies which add-subtract or adjust the factors into the PCM Algorithm which includes the MAF Sensor and the two HI-LO Inputs-Outputs from the ACC Pedal... Trying to apply the use of the TORQUE Program PIDs to a Mechanical System like the LM7 Throttle Body uses simply will NOT work.

Any "Slow Gas Pedal Response" from the Gas Pedal in your truck can only be fine-tuned by making VERY careful adjustments in the Throttle Cable Housing Position Adjustments right at the Bell Crank of the Mechanical Throttle Body. You should ONLY mess around with those housing position adjusters if you determine that the Braided Steel Control Cables are literally ...falling out of their Semi-Circular Bell Crank Slots.

(2) The Mechanically ADJUSTABLE Throttle Butterfly Plate STOP SCREW:

Unlike the Adjustment Screws on Carburetors where the Air AND The Fuel work together via modulated Butterfly Plate Positions to vacuum in the Fuel for mixing right in the Venturi Throat of the Throttle Body via More Air coming through... The LS Motor STOP SCREW is Preset at The Factory.

Ergo... You should NEVER adjust this Throttle Plate Position STOP device unless you are intimately rebuilding the Throttle Body with a replacement Butterfly Plate and installing New TB Plate Brass Bushings.


(3) The NON-ADJUSTABLE IAC (Idle Air Control) Valve:

The IAC Valve controls how much air enters and by-passes the Throttle Body Butter-Fly Plate when the Engine RPM is low or near to Idling to prevent a STALL condition. This device CAN fail if the Air Channel it meters air through gets CLOGGED UP.

Also, since this Wide, Conical Pintle is governed as a VERY Finely controlled Electro-Mechanical Solenoid... If the Inner Coils of the IAC Valve get damaged or somehow short circuit, the Mechanical opening and closing of the Conical Valve End will not work. The IAC Valve is held in place on the Throttle body by Two Small Fasteners and is NOT position adjustable.

If the IAC Valve requires replacement, then the Throttle Body should be completely removed from the Engine and Properly Cleaned first. The Air Box should be washed out clean and the Old Air Filter should be replaced at the same time to see better Engine Idling results. If a K&N Style High Flow Filter-Breather is installed...it should be removed, "Washed Clean ...with Kerosene.." and then carefully dried, re-oiled and re-installed.

Electronic Throttle Body Control vs. Mechanical (Cable) Throttle Body Control


How the Mechanical Throttle Body Functions:


How the Electronic Throttle Body Functions:

 
Last edited:

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Original poster
Member
Jul 21, 2020
55
Miami
Wow. Did not know that the PID for throttle position on the torque for my drive by cable is that irrelevant. I will disregard. So my question remains.

Why do my idle misfires go away when I turn my A/C on? And even more important, is there no adjustment to help make that stop?

So I guess given the information provided, the first step is to remove and clean the throttle body since I have already removed, cleaned and installed the IAC with the battery cable disconnected for 30+ min.
 

mrrsm

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Oct 22, 2015
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Tampa Bay Area
Subtle issues with Vacuum Leaks around the Intake Manifold in the Early LS Series involved replacing the OEM Gaskets with a Modified Set to solve this issue. This Linked Article is a "Relevant Read" on the matter.

Remember that at the point of having ADDITIONAL UN-METERED Oxygen Rich Air "sneaking" by at Idle when the Vacuum Forces inside the Intake Manifold arguably are GREATER will cause the affected Cylinder Bank to misbehave.

In some cases where BOTH IM OEM Gaskets have gone sideways... You'll get Bank 0, Bank 1 (or Bank 1, Bank 2) "Rough Idling" and occasional Misfire Codes:


As mentioned by @Mooseman in another similar Thread... It should Not be Necessary to remove the Negative (-) Battery Cable for 30 Minutes on any Mechanical, Braided Steel Cable Controlled Throttle Body. The "Finer" aspects are always governed strictly by How Hard the Driver Mashes Down the "TRUE" Gas Pedal along with a Well Adjusted and Working TPS . :>)
 
Last edited:

budwich

Member
Jun 16, 2013
2,027
kanata
how many miles do you have on the engine? Possibly a timing chain problem.... guess.... at idle, chain is somewhat slack / lighter over all tension while under load, maybe more well "seated". Look at the fuel trims at idle without and without AC. also look at timing advance.
 

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
Ok. Hopefully there is some other members who have the drive by cable throttle who can shed some light on this. Thanks again for your continued insight.

Any thoughts on what the 221143 PID could be expressing?

I have no data accumulated for that PID yet. Only discovered that one recently. Will add to my Car Scanner sensor list and begin data acquisition. Will post anything found over in the scanner section/pid thread unless I find it is related to this thread.
 

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Original poster
Member
Jul 21, 2020
55
Miami
Thanks MRRSM for that info. I am really grateful for the amazing amount of knowledge you guys provide. This forum is so much better than others I have been involved with. Sorry for the delay in getting these back but the honey do list never ends.

The info requested is outlined below: (note, known valve seal issue on cylinder 3 pic attached. Funny thing is that this cylinder shows no misfires at any time). Misfires are random on most cylinders except for 3 and 4 which never show any. Small counts, max 6 on any one cylinder mostly 1, 6, 7 & 8. No misfires A/c on.

Year. 2002
Odometer. 210,000 miles
Engine. LM7
Rpms at idle. 550 A/C on and off
Temp 197.8 A/C off. Same A/C off
Load. 1.96 at idle A/C off. 2.35 A/C on
Timing advance. 17 to 20 fluctuates A/C off. Same A/C on
Vacuum. 19.9 good snap throttle drop to 5 and return to 25 then back to original value. No pulsation with A/C off. 17.5 A/C on no pulsation
IAC count 42 A/C off. 73.0 A/C on
MAP. 35 A/C off 42 A/C on
EVAP 18.6 A/C off. 18.5 A/C on
MAF. 5.1 A/C off 6.5 A/C on

The following readings are closed loop fully warmed up. (few misfires reported during open loop). A/C off or A/C on

Bank 1
STFT. -2.31 to zero to +2.31 at idle switches good, maybe a little slow. Spends more time negative than positive. Same A/C on
O2 range. .3 to.7. Has sum humps at .7 before dropping. Same A/c on
LTFT. Less than +5 at idle. Mostly +2.34 to +0.78 slow to adjust for negative STFT. +5.4 A/C on
Pulse width. 3.0 to 3.2 A/C off. 4.0 to 4.2 A/C on

Bank 2
STFT. Same as above at idle. Switches faster than bank 1
O2 range. .2 to .7. Seems to have some upper humps as well but less
LTFT. Often zero to +1.34 then -1.34 AC off. +5.4 A/C on
Pulse width same as Bank 1 A/C off. Same as bank 1 A/C on

Again, no misfires with A/C on.
 

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Original poster
Member
Jul 21, 2020
55
Miami
Sorry for the delay but I had surgery for skin cancer on my neck. Pretty scary stuff but all is well.

Little update. I testing different scenarios for my misfires and found that I really get a lot of them at deceleration which holds over into idle. Snap throttle up to 1500-2000 and wow, misfires on most cylinders. Read it could be a fuel pressure regulator on the fuel rail. Pulled the vacuum line off but no fuel leaking from the tube or a fuel smell as indicated by most threads in here. No pressure gauge so no fuel pressure #s just yet. Going to harbor freight over weekend to get one. Seems like a good investment. I plugged the vacuum hose when I pulled the hose off and my LTFT went down from +3.34 to below a +1. That seems strange to me. Question, is the FPR supposed to hold vacuum? Should unplugging the vacuum line and capping it with my finger supposed to effect my LTFT that much. Can a partially faulting FPR have a vacuum leak internally without leaking fuel?
 

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
Going to harbor freight over weekend to get one. Seems like a good investment

Some parts houses like Autozone have a tool loaner program that works like this.... You buy the tool, use it and return it and they credit the purchase back. In the end it costs you nothing. As long as you have the cash or credit to float it.

Should unplugging the vacuum line and capping it with my finger supposed to effect my LTFT that much.


I would think not. If you pulled that hose from the manifold end, then check that hose very carefully for condition. Maybe the hose itself or the connection at the resgulator end is old and leaking? If the regulator itself was failing I would have expected a little excess fuel to be getting into the intake but maybe the opposite can happen. That would depend on the construction of the regulator I would imagine.
 

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