okay guys i have a 1985 vette with a Zf6 swap it was experiencing a world of issues and it seems most are fixed, but the car has a odd issue it will start with no trouble codes but will need the gas held down or it will stumble and die, but if i unplug the EST wire and start the car then plug the EST back in it runs perfectly like a bat out of hell and it throws the EST code from unplugging and starting it up????

Thanks for any and all help guys

 

Go to your FSM and read the section on fuel enrichment/start up.

it explains the pedal position and how the ECM looks at TPS as a clue to a flooded engine. If the pedal is down during cranking it thinks its flooded and cuts off fuel.
The EST is most likely an OL thing.

 

thanks for your reply but it starts up perfectly fine its keeping it on that is the problem after its been started?? but if i unplug the EST it starts perfectly and stays on with little hesitation and after a minute or so it starts to idle perfectly and drives great with lots of power then starts back firing around 4300rpm

 

Was the trans an automatic before you put the ZF in it?

I suggest a minimum idle adjustment:

http://forums.corvetteforum.com/1570563689-post1.html

 

i will try the min idle speed, the car acts like it wants to idle at like 400 or less rpm

 

Is the TPS right? .54v idle?
If the idle screw has not been messed with, then it should be where it need be. The IAC does 99.9% of that job and contrary to popular belief, it does not need us to play around with the min idle screw. Unless the engine has major mods, the IAC knows what to do.
The misfiring at high rpm is a clue to something. has the dist been cleaned well? all the plug-in connections are clean and tight? Often a high speed misfire comes from dirty connections that cause a slow spark or a weak spark. Take a look at the coil and the wires coming from the coil to the plug in connector. That's a great place to have poor contact.

As stated before, the EST connector is making the ECM stay Open Loop where the prom and the many sensor inputs are utilized. Could a faulty sensor cause an ignition problem? Possibly...its a chain of events that would take place and not a direct effect. The temp sensor might cause the ECM to think its warm when its not, or vice versa...I've seen that a bunch of times.
I'd start by going thru all the ign system pieces and clean and test, then move to all the harness connections under the hood. ESPECIALLY the jumper pole or the hot wire connections at or from the battery. THAT can cause every weird symptom known and then some...Been there done that...Jumper pole.
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I went back and re-read your original post and now seem to understand the problem a little better.
Go back and check the coolant temp sensor AND the CS injectors plug and harness. This could be a simple problem of cold start involvement. If the ECM is not seeing the true temp, then it does not know to add CS to the cranking. If that's the case you have to give it throttle to keep it running till it finds a way. About 8 seconds for the ECM to sort thru a fresh start up.
Try the temp sensor. Be sure you look at the right one, not the fan switch or the display sensor.