Series 5 13B 6-port with mild porting won't hold an idle after engine install. There are a few thousand miles on the engine, and it was holding 110 psi compression in the donor car. It also idled perfectly on a stock ECU, rev'd under load smoothly to redline, etc.

The recipient car was able to hold an idle before installation of the "newish" engine.

Initially, we were thinking something isn't connected properly, but we checked all electrical connectors, air and vacuum hoses (there aren't many left, since emissions rack is gone), capped all unused vacuum nipples.

Sprayed starting fluid around the engine, intake, throttle body, etc. to detect vacuum leaks. Found a minor leak around the ACV block off plate, which we fixed with a gasket and sealant.

The ECU is seeing all sensor inputs and hasn't thrown/stored any codes.

The car will not hold idle off throttle. I have to give it at least 10 to 20% throttle to keep the engine from stalling, which allows me to hold it at 2000 rpm. With some finesse, I can reduce throttle to get down to 1500, but it's essentially impossible to keep the engine running below that.

Logged some data between some adjustments to the TPS, idle adjustment screw (top of intake plenum), fuel, and retarding the timing.

AFR is in the 18 to 20 range during all the runs, even after adding fuel on the map. It stays in that range while idling at low throttle.

Logs and chart pics are attached.

"Idle" 1: initial state, before touching idle screw / TPS, basically keeping the idle at 1500 to 2000. Added +15% to +20% fuel in the map between 0 and 2000 rpm at MAP of -18 to -10 (basically, the idle area). Also lowered the Zeitronix narrowband switching point to 13.0 AFR.
"Idle" 2: Adjusted idle set screw and TPS. Some surges to 2500 rpm as I tried blipped the throttle to prevent a stall.
"Idle" 3: After some more adjustment and retarding the timing, plus adding more fuel in the map. With some effort, I can keep the idle at 1000 to 1500 rpm now, and it periodically goes into a surging idle mode.

Notes:

I scaled everything to display on one chart with a single axis, so:
a. RPMs are divided by a factor of 100
b. Primary Injector Pulse Width is multiplied by 10
c. Narrowband O2 voltage is multiplied by 100

I did not log AFR (pin 13F output) because I had forgotten the scaling function for the Zeitronix and didn't have time to log it against the gauge and guestimate it.

 

Same data logs. Parameters vs. RPM on x-axis (instead of time).

The more "static" parameters such as temperature are omitted.

 

Questions:

1. Does this look more like a fuel delivery issue, airflow issue, phantom vacuum leak, or timing problem?

2. Are the parameters within the expected ranges? (e.g. airflow, MAP, injector values) Has anyone logged a healthy idle to check the normal values?

3. I'm thinking of checking voltages at the BAC connector terminals. Does anyone know what these are supposed to be at idle?

 

4. What parameters are helpful to log for troubleshooting idle?

BTW, at high throttle or WOT, I can see the AFRs dip down into 11s by ~7500 RPM. I can see the secondary d/c and pulse width rise, and the primary / secondary ratio fall so it's definitely getting sufficient fuel there. I've only tried this in neutral; haven't driven the car yet.

 

really there isn't much to "tune" at idle as the idle map is closed. If it won't idle its because there is a vacuum leak, the wrong injectors are installed, the wrong pre set is selected, or something is broken.

The only time my car wouldn't idle is when I installed the n390 afm (cosmo afm). No matter how much fuel I tried to add, or what I adjusted the variable resistor value to, it refused to idle. You can't do anything to change idle aside from tricking the ecu by selecting a different injector pre set than the actual injector installed.