how to actually adjust TPS voltage?

[DSteck]

I'm ready to blow my damn brains out with this thing.



I set up a graph to show the follower airflow against engine speed. The line that is steady represents 0 follower airflow at 900rpm, which is commanded idle. I played with it for a while, and it was pretty stable in neutral, although it'd still want to dip a lot. Follower would ALWAYS go away right before it dropped to idle speed, though. In gear, though, it's horrible. If you're just sitting still or at a really low roll, and you blip the throttle, it'll want to die. If you're going downhill, it'll stay running and return to idle perfect. On level ground, it's hit or miss. Going uphill, it dies every time.

I adjusted the blade to get IAC counts down to 35-40 in park/neutral at operating temp, which is about 178º for this thing. I consequently reset the TPS so it was at about 0.61-0.63V at idle. TPS stays at 0% with key off, 0.4% with key on (no flickering to 0.8%).

I moved the IAC vs. Effective Area table over to the right 3 cells just to make it slightly closer to actual airflow. I also set the base running airflow to exactly what the scanner was reporting, and then started screwing with startup airflow from there to get it to fire. When it's hot (again, 178º F), it fires up and idles perfect. However, apparently after it cooled down for a bit and the kid went to start it again, it was surging really bad on startup. I'm pretty sure that's because of the half-ass changes I made to startup properties in an attempt to get away from inflating the base running airflow to make it start.

I'm going to try and get the car dropped off with me so I can just sit down with it and just get it done... but I'm kind of at a loss right now. I'm just shocked as to why this one is giving me so much bull shit. Injectors are Racetronix 42lb injectors, so I didn't have much info on them. The only mods on the car are the cam, which is a 227/231 0.617"/0.613" 113 LSA and headers (well, 4000 stall too). Yes, the car is in MAF only mode right now because it was originally a rush to get it ready to go to the track, so I was super pressed for time.

Help me Obie-Wan, you're my only hope!... before I paint the walls.

[Frost]

Need to either zero LTITs or log them and add STITs as well. At a glance, it looks like it needs more throttle follower. The amount added is VERY small. You can add a lot and use a more aggressive decay down low. It's all gone by 1500-1600 RPMs. The idea of it is to slow the RPM fall. The other reason to remove LTITs for the moment... If it moves to 2g negative at return to idle (from 0), it will pad things a bit. As it is, as soon as the TF decays, adaptive idle takes over at 1600 (throttle is closed, RPMS are in fall) but it doesn't 'know' that the car is in return to idle, it thinks idle. It just sees 1600 RPMs and instantly goes negative and applies the LTIT's learned negative value. This pulls the car down further, makes it fall faster. Log the IT's and you will see them act (update) the second that the TF is gone.

Try this tweaked follower setup and use this cfg to log.

[Frost]

The joy of IAC cars.... if you are used to DBW, you will grow to despise the IAC.

[ElecTech]

The joy of IAC cars.... if you are used to DBW, you will grow to despise the IAC.

The LT1 IAC cars aren't near as finicky. As long as they have enough base air and you can get most of it going through the manifold idle circuits, they are fairly tolerant.

[DSteck]

The joy of IAC cars.... if you are used to DBW, you will grow to despise the IAC.

I'll try the changes you made. This is the first cable throttle that is pissing me off beyond belief. I'm beginning to wonder if the IAC is sticking, because it always seems very slow to respond compared to every other car I've done.

[Google]

one thing that i seen was that when you blip the throttle the iac counts drop from 92 to 69 which makes me think that the stit is adding airflow at idle and when you blip the throttle the stit go to 0.00 and when it hits adaptive idle the stit's can not add it back in fast enough. your max ltit in p/n and in gear is set to 0.50 log your stit and ltit and set your ltit max to 3.00 to 5.00 untill you get it dialed in. just trying to help you out

[DSteck]

So I tried the file from Frost and it was even worse. It didn't even try to stay running. I noticed that if I forced the IAC to 120 counts for a short period when revving, it'd recover. I ended up multiplying the follower airflow table by 2, and then multiplied the decay by 2. I also added a 0.2 delay at 0mph. I kept this delay up to about 10mph. The follower doesn't decay out before returning to idle, but it doesn't die. It comes down to about 1050rpm and sits there for about a half second, and then sets down to idle. It still isn't perfect, and will still die on rare occasions. It just wants to die so freaking fast, and it doesn't make sense. The blade is cracked open pretty far yet it still is super sensitive to running out of air. I'm going to keep playing with it. It seems like it does best with a huuuuuge cushion of tons of airflow, and then take it out quickly. I'm just absolutely puzzled as to why a small cam needs the blade cracked open so damn much to get IAC counts down.

[GPGTP]

what ever happened here?

[DSteck]

I found a method that works for me to dial it all in.

[Pulse_GTO]

I found a method that works for me to dial it all in.

Care to share?

[DSteck]

It's not really easy to put into words. You just have to play with the throttle follower settings to find a happy medium of setting the idle down from various RPM blips.

[GPGTP]

can you be more specific? was it the follower?

[GPGTP]

ah, i see thats what i figured

[JamesLinder]

I was having problems with TPS not reading correctly, which of course will not allow the start-up idle routines
in the PCM to operate correctly among other problems this causes since quite a few PCM functions require TPS
position as an input parameter.

What I discovered yesterday (Dec 3, 2013) with my 2000 SS Camaro (OEM PCM, throttle cable IAC-equipped
throttle body) is that even if you unplug the TPS harness and turn the key on, turn key off, reconnect the TPS
harness that this does not necessarily reset the TPS to zero; in fact, it did nothing. From readings on HP Tuners
scanner it was obvious that the TPS sensor was sending pure crap to the PCM, and when the throttle was closed
it typically was at 2% and at times even higher.

Once I removed the 2 PCM fuses under the hood (which has same affect as removing battery cable) then the
TPS sensor finally returned to the state required for it to relearn closed throttle as zero % TPS and for it to of
course completely relearn everything to do with idle air trims. This completely solved the problems I was having.

Evidently, when tuning, especially if changing TB blade location with the adjusting screw, it is not rare for the
TPS sensor calibration to become corrupted, or in other words, FUBAR. You can tell when this is the case
because the scanner will yield erratic TPS readings when you operate the gas pedal through its full range with
the ignition key on and the motor not running. Basically the readings you will see are completely random and
make no logical sense at all.

When your TPS sensor loses its mind like this, there is nothing you can do other than disconnect power to the PCM
to eliminate the problem. You will probably think you have a bad sensor because the readings are so ridiculous,
however it has just lost the ability to communicate any meaningful readings to your PCM.

[xx_ed_xx]

Old thread same problem

I am having the exact same issue MY GOD is it annoying. I did the battery reset i ran new grounds to pcm. cold no issue. Heat soak start tps reads .8 percent and starts idling all kinds of goofy then it will idle fine then it will move up and down a few hundred rpm. unplug tps settles down exactly how i want it to idle.

And i feel the same way ready to drive this damn thing off a cliff.

[DSteck]

I've had a couple cars where all new wiring had to be run in order to get stable tps voltage.

[mightyquickz28]

I had this same issue yesterday. Thank you soooo much for posting your experiences DSteck. After fighting the high idle, rich AFR and inability to reset the TPS percentage. I cussed, closed the hood and came inside the house to scan the internet. I found 100's of threads but yours had the solution. Getting the TPS voltage from .4 to .63 allowed me to reset the TPS % (FINALLY!). Once it was reset and I started the car, it idled at the commanded 750 RPM (as opposed to 1,250), the AFR went from pig rich (10.x) to 12.x(yes, still rich, but now I can work on that).
Thanks again for putting your experience out here.
David Wilson
96 Z28 - Blueprinted Forged 5.3, PRS Stage 2.5 heads, Isky Triple 12 cam, PT7675 Turbo, 127# Bosch Inj, Transbraked 3800 stall TH350

[reubone]

is there a table for setting the maximum allowed tps % for idle controls?

[reubone]

ok so no one knows.

[ElecTech]

ok so no one knows.

There are, in some cases, but you haven't provided any information on your application or a sample file to help with.