I cant get this engine to idle smoothly, ever since I changed from 305 to 350 with the same TPI setup.
The sensors required have been changed and cannot seem to get a smooth idle no matter what I try, with no codes.
I noticed my fuel pressure isnt bang on every time I start the car, today for example it was idling at 30-35 psi, where most it would be 35-38 psi at idle.
The fuel pump is new all my sensors are a year old.
Any ideas?

 

Which injectors did you use? did you follow this outline? The 305 19lbs are too small plus the prom in the ecu needs to be replaced with a 350 prom

http://tpiparts.net/305_tpi_to_350_tpi_conversion

 

ECM + prom for 350, injectors are new 21s, knock sensor, spark advance changed, everything needed is changed.
Fuel filter and pump are changed, IAC TPS is new, Distributor is new, even bought another harness and ecm+prom to make sure thats not the problem.
It drives fine, no issues but just the idle is never smooth and the engine shakes.

 

Have you taken a vacuum reading? It may not be the computer control system. It could be a bad wire, plug, stuck injector or even a valve too tight. What is the condition of the 350? is it a new build?

 

I can be tricky sometimes getting the TPS set just right. It took a good couple of weeks making small adjustments on my TPI 383 to get it just right.

 

Its a rebuild from last year, checked for leaks, everything is solid.Vacuum leaks were the first thing I checked for.
Could the fuel relay cause anything like this?

 

If the fuel supply system was intermittant you would notice it in the fuel pressure.

If you can try to get a good scan tool and look at what the sensors are saying to the ecm.

Look for TPS or CTS irregularities.

Have you set the minimum airflow on the engine since you put the TPI on the 350? It is going to be different on a 350 than a 305.

 

I need to borrow my mechsnics scan tool again, but Im using the rubber elbow from an 88 GTA and from the MAF to filter my own custom cold air.
My next diagnosis is using parts from a stock working 89 GTA and trying the TB and computer with my prom.

 

Maybe you need to adjust the IAC valve. Theirs a how to in the tech articles.

 

Follow this link. Tells you exactly what needs to be changed. https://www.thirdgen.org/forums/tpi/...-swap-ecm.html

I had the same problem too. I fixed the problem when I noticed some white chalk looking marks on the exaust manifold. Upon further inspection, I realized that the spark plug wire was arching onto the header. So I hung the spark plug wire on top of the smog tubes and my idle went smooth agian. Make sure that your wires arent crossed. May be arching. Good luck bro.

 

Ouch, thats brutal.
I have been though a few wires from burning on the headers so I got looms and boots, thats not the problem but still thank you.
The basics are really vacuum leaks and if you wires are burnt and I wish it was something obvious to detect.
A buddy of mine is a mechanic says the car is cursed and I shouldve stuck with a 305, I dont like that comment.

 

Try unplugging the timing connector, to put the ECM in base mode, of course check the timing, use spray choke cleaner to quick check vacumn leaks and pinch off vacumn lines. Also you can disconnect 1 plug wire at a time and see if you lose the same rpm from each, or unplug 1 injector at a time. You need to qualify the basic engine. Also the EGR could be leaking internially hard to get to but possibly take a extension or long rod and tap on it. Hope this helps GG

 

Another issue could be with either the Ignition COntrol Module or the pick up coil inside the distributer.