I have a 1990 9C1 5.7 in my Land Cruiser. It has the 1228746 ECU (came with the engine). I almost feel like starting over with a 7727 ECU just so I can better read and mod everything, but it hasn't been an issue until recently. Note: ever since new Tuner Pro shows error codes 24 (VSS) and 42 (EST), no check engine light and has run perfectly until recently. I don't see any way to clear and reset these codes.

A couple weeks ago about 2 hours into a wheeling trip the engine stalled at idle. It had never done this before. It happened once more that day. No check engine light.

The next day I hooked up my laptop and couldn't see anything odd. Since I had spares I swapped out the IAC and EST. Everything ran fine on short drives. Base timing was right on. Injector spray patterns looked normal.

Yesterday I went on another long trip. About 2 hours in (heat soak?) the stalling began again. No engine light. Restarting the engine takes lots of cranking and a bit of throttle. I noticed that the injectors were noisier than I remembered. The engine stalled about 40 times before I made it home.

My data logs from 2017 show idle RPM is between 600 and 650 (my expected normal). IAC steps around 50 at idle, TPS volts .62

I ran a data log yesterday in my driveway after I got home (hot from 10 hours of driving). Idle RPM was 550 to 625 stumbling down to 500 (where it stalls, stall saver not quick enough?), IAC 11 to 18 (very low compared to 3 years ago), TPS .62v.

The only changes I ever made to the tune was changing the stoich (14.4) for our local fuel and removed the TCC locking values because my TC has it's own controller. I had to be careful since the $61 mask is not well built out.

The bin does show "Idle - Target RPM (a/c off)" is 550
"IAC - Desired C/L Idle Speed"
675.00
675.00
675.00
650.00
625.00
625.00
650.00
700.00
725.00

Suggestions? Buy another IAC?