350 mag mpi back to running rich on cold start

[cappie]

Changed IAC and coolant temp sensor. Cleaned throttle body, quickleen in fuel. did a complete tune up and it worked for a few start ups. Now it is back to running very rich on start ups. Once it warms up it clears up.

Any ideas would be great

 

[joncrisler]

Re: 350 mag mpi back to running rich on cold start

I thought engines were supposed to run rich when cold
That said, you hit the obvious things I would have checked. Has the engine harness been altered / repaired ? I wonder if a wiring problem is affecting your engine readings. Also, what year? would there be an EFI firmware update that would be appropriate ?

 

[Don S]

Re: 350 mag mpi back to running rich on cold start

Merc has been making 350 Mag MPI engines since 95, and they are not all the same.
Got a SN for your engine