Drifting TPS

[dfarr67]

What's the experience out there?

Toyota 22RET with aftermarket ecu.
- warmed engine running at idle NO throttle action.
- TPS voltage is observed to drift up out of idle window and engine surges, resets and starts over.
- this isn't a fast cycle maybe once every 30 seconds.

[steveo]

probe reference voltage wire at TPS (the voltage coming from the ECM to the TPS). if it varies then it's an ecm or wiring issue or something. if it does not vary but the tps voltage log at the ecm varies the tps is hooped.

[MO LS Noobie]

It is possible your base idle speed is set incorrectly. When it is idling correctly what is your TPS voltage and your IAC (Idle Air Control) percentage. Another issue that comes to mind is a loose connection on your negative side of battery, to engine block and to the body of the car, and also the PCM.

[dfarr67]

Sorry for the late reply- got into the interior/carpet/sound system- about to dive back into the ecu wiring.
Another question- this has the 90's Ford pwm iac- is the airflow directional?

[MO LS Noobie]

Yes, directional. If you unplug the IAC, does it still surge? Unplug he oxygen sensors, do hard reset (disconnect battery and short cables together with 20 amp fused wire for 10 minutes), then restart engine with O2's and IAC still disconnected. Still surge?

[dfarr67]

Just started digging into the harness- have a couple other issues before looking back at the TPS. IAC- turns out the switched 12V+ and the ecu (-) control were wired backwards (my reading shows pos is to the connector lock side). I was asked to replace the IAC- which I did with zero change in behavior. This IAC is for a mid 90's application FOTE-9F715-CA, I assume they have internal diodes and can I assume that both of these are bricked or (hoping here) that once the wiring is corrected they will work as intended- I'll find out soon enough.

[MO LS Noobie]

The reason for the prior post was to rule out a vacuum leak. Has this unit ever ran correctly, or is this a fresh start?

[dfarr67]

A fellow wired it, another guy tuned it- so it does run but hasn't been put into service. I'm finding wiring issues I need to address, fuel pressure sensor is not working, engine light not working, IAC not working, small things that nothing was mentioned. I could solve the IAC completely by reinstalling the 22RE mechanical IAC but it shouldn't be that difficult. So although it runs- it's a fresh start for me.

[MO LS Noobie]

I always recommend that people fix what they know is wrong first. Then tackle the other stuff. The reason I'm so focused on the idle speed and mixture is that if the computer sees idle on the TPS, and it has too high of rpm, it goes into fuel cut. It can be difficult to diagnose something without actually having hands on it.

[In-Tech]

Hiya,
Yes, fix it like it is stock, keep everything in stock ranges, especially TPS voltage(with bigger cams drill a largerr hole in the TB if needed and/or slot the TPS .5-.6v), do the tuning as if it's stock. Then after tuning, ANY competent person can diagnose it as stock. IF the tune is right, diagnostics are the same.

[dfarr67]

I hear you- this is one of the last non stock projects I'll undertake and the second mistake is that although the ecu is a decent unit- it is unheard of in north america so support is an issue if like me the expertise is lacking. I haven't touched the throttle blade adjustment as of yet but the idle isn't fast at all, all problems so far are sub 900rpm.
https://controls.is/shop/ecu/lpc8gen2