I just installed a new 355 into my 91 rs. I start it up and it idles like dog crap when it's cold. it idles like dog crap when it's hot. However when under load it will perform very nicely. When it comes up to operating temp the service engine light comes on. I scanned the system and found a code 42.
EST low voltage or
ESC faulty operation
I didn't get this code when I had the old engine in the car. I disconnected my EST to set timing and since then have disconnected my battery and cleared the codes. this one still comes up and only comes up when the engine reaches 220 on my temp gauge. I never played with the ESC. I did replace an eye-connector on a ground wire for the ECM that bolts to the back of the head on the left (drivers) side. it was a light tan wire with a black stripe. I suspect this is the ground for the EST connector but, I don't know for sure and I don't know if this could be causing the problem.
Could this be a false code due to a bad O2 sensor?
Keep in mind it runs the same in both open and closed loops.
Where do I connect my meter to find out if my EST connector really has low voltage? How much voltage is it supposed to have?
How can I check my ESC module to make sure it is ok?
Lastly, what does the ESC look like? Is it that flat, rectangular sensor located right in front of the relays with about 5 or 6 wires coming out of it?

Help.

 

get car to operation temp and then disconnect the est and see what happens to the rpm's. should go up I think not sure but the rpm should change. you can also tap just above the knock sensor and the est should adjsut the idle in some way by changing the timing through the est mod.