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I have been chasing this problem for months now.
History: Developed an intermittent stumble/ misfire. Was throwing a random misfire code. Then overt time it started to just die while driving occasionally. Things got worse (and I had too many other projects to deal with) until finally it wouldn't start unless I mashed the throttle. To be clear, it will start, then die immediately. To stay started, I have to mash the throttle.
Here's what I've done:
- Tested temp sender
- Cleaned and tested MAF
- Tested TPS
- Tested fuel pressure: steady 43psi, even after sitting for long periods.
- Replaced plugs (old ones looked fine, none fouled)
- Replaced O2 sensors (Bosch)
- Replaced fuel injectors (new, not rebuilt 275 cc/min)
- Replaced ICM and coil

The wires and Opti (AC Delco) are fairly new (mebbe 30K miles). Fuel pump has mebbe 5K miles and fuel pressure is a steady 43psi, even after sitting for long periods. (I tested the old injectors and 1 or 2 seemed to be leaking).
There's no codes.
I noticed no change after plugs or injectors. After coil/ICM it still hard starts, but runs MUCH better - much zippier.
Once it's started, it runs great. But it ALWAYS starts hard (hot or cold) and needs WOT to get going.

I've read thru about 100 threads on here about similar issues and nada. Any other ideas would be much appreciated.
 

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I would put car on an obd2 scanner that does real time sensor data. See what the sensors are reading as you try to start engine, & when it runs.

If no clue to what sensor readings should be, PM me with your email address. I'll send you the pdf file called "scanner readings and what they mean.

My best guess is that the pcm is commanding injector on time much to long. By using wot, you are cutting fuel injector operation which clears the flood problem. Engine starts & runs.
 
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