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Toyota ECU's depend on an IGF signal from the ignition module. My MR2 had spark, but the ignition module wasnt sending out the proper IGF signal to the ECU, it threw a trouble code, I replaced the module problem solved.
The symptoms were identical to yours, ignition modules can slowly start to go bad. They get worse when they are hot, and eventually they will one day cease working.
The ECU sends an IGT signal to the ignitor module to tell it to spark. When the coil and ignition module creates a spark successfully the ignitor module sends an IGF signal back to the ECU, saying mission complete. The ECU then uses the IGF signal to trigger the injectors.
So, no IGF signal doesnt mean you dont have spark, but the ECU doesnt know there is spark because the ignition module is no longer talking to it, so it will shut down the injectors...
I wrestled with this problem until I decide to actually check my trouble codes... I thought I had a fuel problem because I had spark. As soon as I replaced that module though, the car ran great!
So, moral of the story, try checking your trouble codes. Oh, I apoligize if my IGF/IGT explanation wasnt perfect, someone else could probably say it better. But I got the basic principle correct. I am sure its extremely similiar even though I have an MK1 because most new Lexus ECU's work the same way with IGT and IGF.
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