So, first 10-15 minutes of driving it runs fine. Then once its all warmed up, it falls on its face starting at 5k, then 4k, then 3k. If I turn it off the ignition then start it again, it'll run all the way to redline again, for afEwing minutes,

 

how many miles on the engine?

i had an engine do that many years ago and my conclusion upon disassembly was dead/dying springs on the side seals and corner seals. so maybe try checking the compression?

 

Check the ECU reading for the Water Thermosensor at pin 2I (Green/White wire). W/key to on Should read 2 to 3 volts for a cold engine and .4 volts when fully warmed

 

Diabolical, it has 147k on the clock. If it where something internal, how would shutting it off, then right back on again temporarily love the issue?

Satch

 

Diabolical, it has 147k on the clock. If it where something internal, how would shutting it off, then right back on again temporarily love the issue?

Satch, I like your idea, but I've never tried that before so I want to make sure I get it right. Let me see if theirs sounds about right. Start it, run it for just a few, then shut it down while still running good and check the pin at the harness side to see what the signal is coming into the ECU? Then drive it, when it screws up, kill the engine and check it again? I'm guessing everything off during the disconnect, then ignition on when testing, or have I got this all wrong? Thanks!

 

You test pin 2I at the ECU after the car has been sitting overnight which makes it a cold engine and compare the results to spec. Then you start the car and take a reading as the car fully warms up. And you don't have to disconnect anything. The tests are done w/key to on when cold, engine not running. And either w/key to on and engine running after fully warmed or w/key to on and engine off after fully warmed.

And you can keep the meter connected to pin 2I so you can watch the reading at all times either when it's running right or not.

 

And pin 2I is a Green/White wire found in the 2nd largest ECU plug, top row middle wire (5th from the right or 5th from the left).

 

nevermind. i'm an idiot. i somehow seemed to miss (or ignore) that part of your post.

yes, in addition to 5000 RPM thing when hot, mine also had some serious hot-start problems. sorry, i screwed that up.