Unsolvable Idle problems

Hey Ya’ll, I have a 95’ 4cyl 2.7L 4WD Tacoma that has been having some engine issues for a year now and can’t figure it out. The Truck cant hold an Idle and I can get it moving but its sluggish and wants to die. Some days it idled and drove fine. Now it wont hold an idle at all. It will start up and immediately die. The check engine light is on with no codes. The engine has been backfiring

I’ve replace the Throttle body, fuel injectors, fuel filter and tested the fuel pump and it’s good. Theres positive fuel pressure. So I don't think it’s a fuel issue. Compression test is good, all cylinders reading 150. Checked the timing belt and its good. New spark plugs with good spark. MAF is good. New IAC valve. New Catalytic converter and exhaust manifold. Checked for vacuum leaks, none.

I also did an Egr delete. Replaced the entire coolant system. A few new sensors and much more repairs.

At this point the only thing I think it could be is the ECU or igniter control unit. I am lost, if anyone could point me in the right direction.

 

3RZ has a timing chain, not timing belt. How’s the timing?

Not sure if you checked yet, but a common leak issue is with the brake booster diaphragm.

 

If the CEL is on there should be freeze frame data... but is is sounding like the PCM is flaky. Unplug each connector a few times to swipe the contacts and see if that "fixes" it.

 

I mispoke, yes the timing chain. Timing is good, I checked the brake booster line and looks fine.

So I just fired it up and its running fine now. When I was trying to start it 2 days ago it was raining. Do you think it could just be a faulty ECM? I’ll test out the connections later.

 

Intermittants like this are bear to figure out and with no codes you have no true diagnostic direction to go. What was your fuel pressure when you tested the pump? All of your inital observations sure make it sound like a bad fuel pump, sluggish, backfiring etc.

This is a shot in the dark ... take the PCM out and take the cover off and look for obvious signs of capacitor leakage, burn spots, etc. There are a few posts on this forum showing what a bad board looks like. At some point after you have tested things multiple times and found nothing you have to suspect things like the PCM, it is a tough tough call to make to spend yest more $$$ on a part to "test".

 

This will sound weird but have you checked the Air Temp Sensor and Coolant Temp Sensor readings on OBDII scanner with the key on and engine off. Either one of those failed open or shorted will tell the ECU a temp is at the extremes which can cause overfueling or underfueling to an extreme amount. See if the values they're reporting on a cold engine are within 10* of ambient.