Symptoms of a cheap throttle body -- and recommendations for something better?

[JakeRobb]

Spinoff from a digression in another thread:

The engine won't even idle; I have to hold the throttle open a bit when starting, and then continue to hold it there for it to run continuously. Even after doing that for several minutes so that it's warmed up and I can start to see fuel trim values in VCM Scanner, it dies immediately when I let off the pedal. I assume this is an IAC issue due to the upgraded throttle body, but haven't looked into that yet because I was advised to tune VE before idle. This situation has me thinking I should probably do idle tuning first. Or, maybe: does the PCM need IAC calibration data like it does for the MAF? Another possibility: I went with a relatively inexpensive Speed Engineering 92mm throttle body before learning that most tuners won't even bother with those and insist that people use one of the more expensive TBs. Could this refusal to idle be a manifestation of my cheap TB? (I'm prepared to replace it; just hadn't heard about the cheap ones causing this specific problem.)

VCM Scanner shows a maximum of 2.25v from the throttle position sensor. Looking at it physically when the pedal is fully depressed, the blade appears to be wide open. Is this typical of the sort of BS you get from a cheap throttle body?

Wish I had known sooner!

Anyway, on to the recommendations:

I'm set up for DBC right now. I've heard that it's easy to convert to DBW -- just need a pedal and a throttle body. I assume I also need to route some wiring since my factory harness lacks provisions for an electronic pedal. And then I know I'd have to modify the tune for it. Are there instructions somewhere for the tune portion?

What pedal setup will work best in my '02 Camaro in terms of mounting and pedal placement?

Finally: what about cruise control? I'd like to retain that. Does the PCM take over these responsibilities in DBW-land? Can I remove the factory cruise control module (behind/below the driver side headlight)? Do I need to worry about anything with respect to removing the cruise motor mechanism (over by the A/C dryer)?

If I were to decide to stick with DBC, what do you recommend? Nick Williams seems popular, so I assume it's good stuff. ICON seems good as well.

In the DBW world, I think I'd probably go with Katech.

In either case, what else should I be looking at? I'm not terribly price sensitive; happy to spend up to $1000 for the right bit of hardware.

Whatever I get needs to fit be physically compatible with my 100mm MAF and my LS3 intake. And if it will work well with a FAST intake down the road, that'd be cool too. (Not sure I'll ever bother; just like to leave the door open and not have to double-spend.)

[SiriusC1024]

The TPS is the problem. Did you properly do a relearn?
https://www.pcmofnc.com/2021/03/05/i...throttle-body/

[JakeRobb]

Retyping this, as I went back to edit a typo and somehow deleted the post instead. :/ (These forums are really awful to post with on mobile!)

The TPS is the problem. Did you properly do a relearn?
https://www.pcmofnc.com/2021/03/05/i...throttle-body/

Ha! I remember reading about TPS relearn a couple years ago, but had totally forgotten. No, I have not done that (unless by any chance it happens automatically when you Write Entire).

Anyway: I don't have VCM Scanner configured to show TPS%, only voltage. So I don't know if it's reading 0.0%.

I also haven't gotten the car to idle yet at all, so I can?t even get past step 1 of the instructions you linked. I'm guessing my idle troubles are because it's not at 0.0%, so the car isn't even trying to idle. Will check at my next opportunity!

If that's the case (non-0.0% TPS), what do I do to fix it? The instructions you linked seem to assume I'm already past that point.

[SiriusC1024]

Main thing is closed throttle voltage range in that link. TPS has to be within that range in order for TPS reset to work. To reset, verify closed throttle range. Turn off ignition, unplug TPS and IAC, turn on ignition for 10s, turn off and reconnect sensors, verify 0% throttle.

If TPS voltage really doesn't go above 2.25V then that's the TPS or wiring.

[JakeRobb]

Main thing is closed throttle voltage range in that link. TPS has to be within that range in order for TPS reset to work. To reset, verify closed throttle range. Turn off ignition, unplug TPS and IAC, turn on ignition for 10s, turn off and reconnect sensors, verify 0% throttle.

If TPS voltage really doesn't go above 2.25V then that's the TPS or wiring.

Okay, thank you. I'll try it!

I'm a bit confused that it idled fine when I first started it, using the OEM LS1 tune along with this same TB. (Prior to that start, the PCM had been unplugged and out of the car for a few years.)

[edcmat-l1]

If TPS voltage really doesn't go above 2.25V then that's the TPS or wiring.

Or, with an aftermarket T-body, the cable isn't in the proper hole in the arm and the blade actually isn't opening all the way. Very common and easily overlooked by DIY guys.

[JakeRobb]

Or, with an aftermarket T-body, the cable isn't in the proper hole in the arm and the blade actually isn't opening all the way. Very common and easily overlooked by DIY guys.

Pretty sure I have this right, but will verify. I think I remember checking when I hooked up the cable; pedal to the floor => cable arm on the stop and blade parallel to airflow. I'll check it again to be sure.

[edcmat-l1]

I would definitely recommend replacing the TPS and IAC with AC Delco units first thing. Other than that, the IAC passages will need to be modified. I'm sure someone has a video or detailed thread about it somewhere in innerwebzland.

[2xLS1]

Or, with an aftermarket T-body, the cable isn't in the proper hole in the arm and the blade actually isn't opening all the way. Very common and easily overlooked by DIY guys.

OP stated WOT voltage is only 2.25V. TPS reset doesn't change that, only the % shown in the scanner. Also said the blade appears to be wide open. Have you checked the 5V reference voltage and the ground at the sensor? Do some electrical diagnosing. It is a simple potentiometer circuit. Should be looking for a sweep from .5v closed to 4.5V wide open.

[JakeRobb]

I would definitely recommend replacing the TPS and IAC with AC Delco units first thing. Other than that, the IAC passages will need to be modified. I'm sure someone has a video or detailed thread about it somewhere in innerwebzland.

Whoa, I had no idea the sensors inside the TB could be replaced without doing the whole unit! I wonder if I can harvest them from my factory LS1 TB, which I think I still have laying around somewhere. Not sure if the sensor form factor would be compatible with my new setup.

Modifying IAC passages: are you referring to the process where you drill it out little by little? Is that strictly necessary? I was under the impression that you only do that if your IAC counts are too high under standard conditions (engine warm, park/neutral, AC off).

EDIT: the product listing for my 92mm Speed Engineering TB says it "Uses Factory IAC and TPS Sensors". So maybe this isn't the problem...?

[2xLS1]

Whoa, I had no idea the sensors inside the TB could be replaced without doing the whole unit! I wonder if I can harvest them from my factory LS1 TB, which I think I still have laying around somewhere. Not sure if the sensor form factor would be compatible with my new setup.

Modifying IAC passages: are you referring to the process where you drill it out little by little? Is that strictly necessary? I was under the impression that you only do that if your IAC counts are too high under standard conditions (engine warm, park/neutral, AC off).

DBC TPS is easily replaceable. You might be thinking of TPS on a ETC. And even some of those are replaceable

[edcmat-l1]

OP stated WOT voltage is only 2.25V. TPS reset doesn't change that, only the % shown in the scanner. Also said the blade appears to be wide open. Have you checked the 5V reference voltage and the ground at the sensor? Do some electrical diagnosing. It is a simple potentiometer circuit. Should be looking for a sweep from .5v closed to 4.5V wide open.

Not sure why you quoted me and started talking about TPS reset. I never said a TPS reset would change that. I know he stated the blade was open but I posted what did because it is commonly overlooked and he himself said he needs to double check it.

[edcmat-l1]

Modifying IAC passages: are you referring to the process where you drill it out little by little? Is that strictly necessary? I was under the impression that you only do that if your IAC counts are too high under standard conditions (engine warm, park/neutral, AC off).

Do a search. All the Chinese throttle bodies need the IAC passages opened up. Some even need the orifice enlarged.

[2xLS1]

Not sure why you quoted me and started talking about TPS reset. I never said a TPS reset would change that. I know he stated the blade was open but I posted what did because it is commonly overlooked and he himself said he needs to double check it.

Because you said to check the mounting hole when he said it was opening all the way. at 2.25V it wouldn't be anywhere close to open all the way visually unless the reference or ground was way off. The reset remark was in reference to an earlier post by that other guy.

[edcmat-l1]

Because you said to check the mounting hole when he said it was opening all the way. at 2.25V it wouldn't be anywhere close to open all the way visually unless the reference or ground was way off. The reset remark was in reference to an earlier post by that other guy.

That is correct. I even make my guys double check shit. I don't take anyone's word for anything. It was worth mentioning. It would not surprise me if he came back and said that was the reason and he was initially incorrect in his assumption that it was opening all the way.

[2xLS1]

Take it easy. I'm on your side on this forum.

[edcmat-l1]

Take it easy. I'm on your side on this forum.

LOL didn't think I wasn't taking it easy.

[SiriusC1024]

Because you said to check the mounting hole when he said it was opening all the way. at 2.25V it wouldn't be anywhere close to open all the way visually unless the reference or ground was way off. The reset remark was in reference to an earlier post by that other guy.

If TPS voltage really doesn't go above 2.25V then that's the TPS or wiring.

I mentioned TPS reset because if you want to start troubleshooting make sure the procedure is correct. If he couldn't get the correct closed throttle voltage that would indicate his TPS is mounted incorrectly, and it would be why WOT voltage is so low. Aftermarket TB and such. I had to elongate the mounting holes to clock the TPS for it to work on my TB.

Nice try, though.

[JakeRobb]

Got some new info:

1. I evaluated the setup as-is. By actuating the throttle by hand (at the throttle-body end of the cable), it opens such that the blade is fully parallel to airflow.
2. However, by actuating it via the pedal, it only opens to about half that! (This is where I saw 2.25v) :facepalm:
3. Back to actuating it by hand and watching the TPS % in Scanner, I saw 0.14% -> 100%. That explains why it won't idle!
4. Did a TPS relearn. Now I see 0.4% -> 100%! Success!

My kids are asleep and the garage is directly below their bedrooms, so I couldn't start it up and see if it will idle now. I'm somewhat optimistic, but prepared to have to mess with IAC and possibly do some drilling before it's totally happy.

I checked the pedal box, and there is nothing interfering with the pedal travel, so now I just need to figure out how to adjust the pedal/cable. I know of a couple spots along the cable where you can make adjustments, but those are maxed out. If anyone knows the LS1 F-body setup well enough to give advice, I'd appreciate it -- but I'll go ask on LS1Tech, as this is not really a tuning question.

One followup question: the voltages I saw from the TPS ranged from 0.14v (0%) to 3.92v (100%). Should I be concerned that I'm not seeing something closer to 5.0v? If so, what might I do about it?

[SiriusC1024]

See the cruise control module on the passenger fender well? I opened it up and put a cotter pin through the holes in the cams to lock them in sync. Unplugged the module. There's probably a better way, but I didn't bother with it because I never use cruise control.
cotter pin.png