BP4W swap into 96 Chassis - Hot restart idle problem
 

Good morning all!

Yesterday I just finished swapping a 2000 model BP4W engine into my 1996 Miata. The only real issue that I can tell is the idle on hot restart. On a cold start, everything is perfect. The idle starts higher, and lowers to comfortable point once warmed up. However, if I shut the engine off and attempt to restart, it'll start, but it seems like it hunts for the idle. According to the tach it appears anywhere from 200-800rpm-ish, before finally settling on a comfortable idle.

A little bit of information on the car:

the PRC was not installed on the 99 engine. I understand the purpose of this was for hot restarts; could this be a player in the idle problem?

I am using the 2000 fuel injectors. From what I've gathered, they are not optimal with the rest of the fuel system, but all the research I did claimed they would work fine.

I did a quick overview of the engine to check for vacuum leaks, but didn't see any.

I am on a stock 1996 ECU.

Are you using the 99 throttle body?

I am not. All sensors, including throttle body are 1996.

I have a 95 with a 99 engine and I found something similar when the vacuum hoses, on the 95 fuel/emission system, come undone. The hoses connect to the intake manifold and to a solenoid mounted on the passenger side, one with blue lines the other with red.

Disclaimer: I am running MS2, tried to get the car back to stock and could not get it to run correctly with the stock ECU and 99' injectors.

Yeah, the vacuum lines didn't want to fit perfectly (I think the VICS solenoid is a little in the way of one of them) but they're on there. Do you think it's possible my ECU had to "relearn" the hot start idle? Today it acted much more well behaved. Also, speaking of MS. Does anybody know why the DIY MSPNP 3 Pro isn't available for the 96-97? I couldn't find it online.

From my understanding the MS3Pro pnp for 96-97 is produced but their bench testing system for them is not up and running or something along those lines, I've been waiting since October to get my hands on one