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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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Under normal circumstances the TV set screw shouldn't need any adjustment. It can actually be detrimental if it was properly set from the factory and was tampered with after installation for some reason. Put on your thinking cap, and let me explain...

The PCM has tables that define how much air should be entering the engine at a given IAC valve duty cycle, which is the sum of whatever air is coming in through the closed TV as well as what's coming in via the IAC at that duty cycle. IAC valves and factory-set throttle bodies have some variance in air flow, but not a lot. The PCM is able to adjust to these minor variances by fine tuning duty cycle of the IAC until it gets the desired idle RPM. You can see how much air the PCM has to subtract or add from these tables by monitoring the ISC_INTEGRATOR PID with a scan tool.

If for some reason too much or too little air is entering the engine, the idle air tables will no longer reflect reality. Take this example...

The engine still needs the same amount of air to idle (let's say .8 lb/min for the sake of discussion). Let's say from the factory .1 lb/min comes in through the closed butterfly valve. That means the PCM needs to command the IAC valve duty cycle to reflect an airflow of .7 lb/min to get that idle speed. Now, if .2 lb/min is coming in through the TV that means we only need .6 lb/min to come through the IAC. The PCM has no way of knowing that, so it commands .7 lb/min through the IAC. Our idle is too high. After a minute or two of the PCM slowly tweaking the IAC duty cycle down, it learns the ISC_INTEGRATOR values and the idle would smooth out for the trip. ISC_INTEGRATOR is reset every time you start the engine.

The main difference between a vacuum leak and a misadjusted TV butterfly is the fact that a vacuum leak introduces unmetered air and causes your idle to be too lean, too high (depending how lean it is) and too much spark advance. Once the engine/O2s have warmed up enough to switch to closed loop, the O2 sensors report the lean condition and the PCM adjusts to compensate by subtracting idle air and adding fuel. Without a vacuum leak and there just being too much air entering at idle, the PCM is still delivering the proper fuel and spark - it will just take a couple minutes for it to relearn ISC_INTEGRATOR.

Now, to cap off this little lesson in PCM idle behavior.... the PCM only uses this strategy when it's in idle mode which requires the TPS to be properly set. If not it will perpetually be in part throttle mode and then you're relying on the dashpot functions of the IAC valve and not idle feedback. So the TPS needs to be properly set with the TV and IAC responding to how the PCM is programmed for all to work properly for a smooth idle.

This isn't the only thing that can cause a low/rough idle, but if all else is as it should be it's something to consider as you troubleshoot.
 

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Discussion Starter · #42 ·
I have air blowing out the vents again and a 96 IAC on order. Can't complain.
 

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Discussion Starter · #43 ·
Installed the new IAC valve and there is no change. It still behaves as if there is no IAC. I wondering if the previous owner got the wires spliced in backwards when he added the 1996 IAC plug. Now I am in search of a 96 IAC pigtail just so I can test it out. Don't get me wrong, I am having fun.
 

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The red wire is getting battery voltage so it is spliced correctly. Next is checking the duty cycle. My Fluke 87V should be able to check it.

I disconnected the battery for half an hour. Started the car. no change. re-flashed the SCT tune after that. still no IAC action.

The TPS is not adjustable so I left that as is. The OBDII can sort the values out.
Also set the TB butterfly by backing the screw out then used a 0.010 feeler gauge then one full turn. The idle was way too low due to no IAC action.
I am determined to figure this out and put a coda on this thread.

Checking the duty cycle was inconclusive. I connected the leads to the plug that goes to the IAC. I was expecting a fluctuating reading around 40% but all I got was a static reading. it would be different every time i contacted the leads to the plug, from 2% to 89%. when I use duty cycle to check the air/fuel ratio on the 86 Mercedes the values fluctuate in real time.
Next test is continuity from the plug (white/Lt.Blue stripe) to pin 21 on the PCM.

One more thing (Columbo), maybe its the custom tune? maybe it's the coolant temp sensor. I noticed the temp gauge in the dash works but I don't see a separate sending unit like the ones that read off a heater hose. So if it is spliced into the temp sensor that feeds to PCM then that could be an issue based on what i have read here on TCCoA.

I do know one thing that is for sure. It's beer:30!
 

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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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Do you have a laptop you can use to hook up your tuner (assuming it's an XCal of some sort) to LiveLink? Monitoring a few of the PIDs might help hone in on the right components.
 

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I have two laptops. one has Linux OS, I use it for writing sketches for arduino projects and python. the other has windows XP for old unsupported software that I like to use. alternatively I have a desk top with windows 10 and a cart . the tuner is sct x4. I have various interface cables but none seem to fit the data port on the tuner.

Holy crap! Shipping is 20 bucks for a 10 dollar cable. No deal.

Looks like a android cable would fit but I threw one away about a month ago.
 
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Is it just a USB-B to USB-A cable? The squarish one to the rectangular one? Printers come with them sometimes; I have piles of them available at work. If you need it PM me your address and I'll mail you one.
 

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Discussion Starter · #48 · (Edited)
my old SCT tuner uses a printer cable but this one is a micro USB. I looked in the box again for the heck of it and there I found the cable hiding behind a piece of black foam.
I guess this is my Easter Egg. :)
42831
 
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Discussion Starter · #49 · (Edited)
I hooked up the tuner to the car and computer and ran a data log mostly idling with a couple taps on the gas up to 1500 ish rpm. The IAC duty cycle is pretty flat at 57% and a max of 64% (tap the gas). I noticed the EGR duty cycle is a flat line zero all the way across. I will run another data log with the engine warmed up.
Still stumped why the IAC never opens. I save the data log as a csv file if anyone would like to look it over.

Thanks Brandon for pointing this software out. I really like it. The computer on a cart works good just cant take it for a ride.
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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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I'd start with these PIDs -

ISC INTEGRATOR
ISC DUTY CYCLE
AIR FLOW #/MIN
LOAD
STFT[0]
STFT[1]
RPM
FUEL SOURCE
TP RELATIVE
COOLANT TEMP
 

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Discussion Starter · #51 ·
I created a data log configuration with the PID's you posted but some are out of the "Verified" scope of PID's.
So I did what I could with the set of verified PID's. I did not use ant that are tagged OBD. I ran a data log with the car at operating temperature and saved it as a CSV file.
I noticed some anomalies. Spit second spikes in RPM for example. I ran the data log mostly in idle and no way did I ever take to 8500 RPM lol. i am hoping this a normal thing with the SCT X4 data logging.

I checked the IAC air inlet with my thumb and found it did have a good bit of vacuum on "return to idle" after bumping the throttle but otherwise not so much if any vacuum. The data log read 48% at idle and that is at the upper end of acceptable. The EGR duty cycle also showed values over zero when revved up.
But still cold idle is stall prone. Idle is smooth just stalls. It's ok once warmed up.

I took a pic of the air inlet tube at the throttle body where my eyes can't see and noticed the clamp was on backwards. It's slots were not lined up with the rubber tabs. While correcting that I noticed a tear at the bottom side of the rubber inlet tube. The tear does not go beyond the clamp area so I think it's okay.

One more thing. The new speakers sound pretty good.

I apologize for rambling on.

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42864
 

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Discussion Starter · #53 ·
I will get a new fresh air intake tube. Shouldn't be too hard to find.

Hi Brandon,
I think the IAC was a red haring. It is drawing vacuum right away on cold starts too. I checked it with a vacuum gauge too. So if it's getting all the air it needs then could it be way too lean cold? Here is a cold start video. I never touched the gas pedal.

 

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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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TPS absolute looks all right - mine usually sits around .185 .. Relative should read at or really close to 0 when the throttle is closed - the PCM is supposed to automatically adjust based on the sensor output.

Load just after startup should almost immediately drop down to 18-20% and stay there for stabilized idle. The IAC should be open only about 35% while cranking based on what I see in the factory calibration.

Can you capture all the PIDs I listed (or as many as you can find) in LiveLink for a startup and upload the CSV?
 

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I watched this guy build this car through Instagram it started out in California and was white, he redid a lot of stuff and including that 96 conversion. Glad to see it fixed properly
 

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Discussion Starter · #56 ·
Thanks Jordan. He had go back to Australia so I picked up where he left off. I'm sure he'd be doing what I am doing to it.

Hi Brandon. Here are some "cold start" data logs I ran to day. the first one includes a stall. The last one I bumped up the TP adjustment so it would not stall. The RPM hunted around for a little while then settled down. It must still be learning after disconnecting the battery last week.
CSV files not allowed as an attachment.
 

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I took a look through your logs. The cold start/stall issue and surging idle looks to be a result of improper idle airflow tables in the tune and/or a vacuum leak. Once it gets into closed loop the idle stabilizes. Just regular PI cams/heads? Stock MAF sensor?

Do you have anything for the X4 in LiveLink that looks like idle air integrator? If so, can I get a look at what that is doing on a cold as well as a hot start? Also seeing the STFTs and LTFTs during a warm idle will help deduce actual fuel delivery vs. what's expected via the various tables and functions. The IAC is all over the place, but I don't see sensors that are reporting data to contradict any other sensor's which seems to indicate they are working normally.

Here is what I have in mine, but this might be slightly different for your processor code.

42877
 

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Discussion Starter · #58 ·
Just regular PI cams/heads? Stock MAF sensor?
Heads and Cams are stock 2004 Mustang. The MAF is stock 1994 Thunderbird.

I tried to add idle air integrator and it was rejected. It was not a validated PID. I'll try it again. The LTFT's are fine and I'll add them to the configuration.

42881
 

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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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OK, I see the same now that I know what strategy your PCM is using.

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Try for it anyway - the lowercase PIDs have a lower update rate than the ones in all caps. IME it's a crapshoot as to which ones work and which don't.
 

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I see a few interesting things in your latest set of logs.

After the car switches to closed loop, it has to command 10% less fuel to obtain stoich indicating a rich condition. After the car reaches normal operating temps however, everything looks spot on.

Have you verified fuel pressure?

How about the tuner, do you know who it was? If it was tuned with a bunch of vacuum leaks, that could explain a whole lot.

Just for the heck of it, try doing a cold start with the MAF unplugged to see what it does.

And yes, I do some flying. Had my PP since 2014. No instrument rating, but I do have high performance and complex. :)
 
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