TBI Throttle Position Sensor?

[Chevrolado]

The vehicle: 1995 Tahoe 5.7L with TBI
The problem: sporadic idle, jumping from too low at 400ish RPM all the way up to 2000 and everything in between. Also occasionally will not start. Then once started, idle jumping again. Will not stay still.

History: this truck had a Venom 400 module put on it (spliced into the TPS wires as directed for install). If you dont know what those do;

Venom Performance Control Module - Venom 400 Engine Management Piggyback
Achieve horsepower gains up to 25% over the mid-range 1,000 to 5,000
rpm. The venom 400 is and add-on control unit that features its own
micro-controller. This module is connected to the vehicle's sensors and
increases engine performance by monitoring the sensors output
characteristics and modifying the input signals to the vehicle's
existing computer. The unit activates at about 25-30% Throttle Angle
and tells the ECU to provide a more aggressive set of fuel and ignition
maps than it would normally provide.

So it had never worked right from the previous owner, so it was turned off, but still wired up. Well the other day I was driving, it started going crazy on idle and jumping all over. I decided, you know what, I bet its this weird splicing in of this box. So I removed it all, electrical taped the spliced portions, and put the wires back into their looms and drove home.. It worked great for a little bit. Then all of a sudden, started going EXTRA crazy.. Then hard shifting into each gear. Then "Service Engine Soon" light.

Got it home, and finished pulling the entire unit out with wiring. So now it's back to stock. It still had the idle jumping issues so I cut the spliced wires and reconnected them with some wire connector crimps in hopes it was just not getting a good electrical current..
I also found this issue in the gasket for the K&N intake:

So after I finished all of the electrical fix and repaired this gasket.. Hooked the battery back up and it started RIGHT up and ran better than I've seen it. Took it for a test drive and it was great all the way to the store. Turned it off, went in, came out it started right up again and then on the way home it went crazy again!! What the heck?
Unhooked battery, waited, hooked battery back up and it runs fine again.. This time not wanting to chance it, drove it to the shop and left it for the mechanic to look it over tomorrow..

Anyone have any ideas?? I want to fix this myself but at this point I'm at a loss. I just don't know enough about these yet.. Any help would be greatly appreciated.

Thanks!

 

[SunlitComet]

can you test you test or clean your iac valve or reset it? i think that it or the map sensor may be your issue. O2 maybe but way on the bottom of list of causes.

 

[Chevrolado]

Not sure. What does it take to test or reset? First time working on a TBI motor and just picked this up last month.
Thanks!

 

[SunlitComet]

remove batt cable for at least 10 sec. ignition on engine off mode for 5 secs. ignition off for 10 secs. consider it reset. testing is much more involved i would need to email the procedure.

 

[Chevrolado]

Hmm. Alright. Worth a try. Thanks for the tip.

It's just weird to me that the thing runs awesome after the battery is unplugged and then it eventually goes haywire again for what seems like no trigger.

 

[SunlitComet]

might have a problem with sensor data that happens in a closed loop or something really out of whack and the computer it trying to compensate outside the learning mode that occurs if battery power is interrupted to the ecm.

 

[retorq]

Looks like you have a cracked vacuum boot on that TBI. Those studs aren't stock, what else is done to this thing?

 

[SunlitComet]

you should never add on modules that alter a sensors output. that can do some crazy stuff sometimes. always alter the computer programming itself.

 

[Chevrolado]

might have a problem with sensor data that happens in a closed loop or something really out of whack and the computer it trying to compensate outside the learning mode that occurs if battery power is interrupted to the ecm.

Hmm interesting. Okay thanks!

Looks like you have a cracked vacuum boot on that TBI. Those studs aren't stock, what else is done to this thing?

Yeah, the studs are for the K&N intake that is on it.
Aside from the K&N, the Venom 400 that WAS on it, and a cat back exhaust.. That's it. Rest of the motor is stock. I think it was the addition of this computer altering "performance module" that drove it crazy.

you should never add on modules that alter a sensors output. that can do some crazy stuff sometimes. always alter the computer programming itself.

I definitely agree with that. I wouldn't have put it on there.. But hey, wasn't my truck until now. :-/

 

[retorq]

I have a use for that thing if you want to get rid of it.