legacycentral bbs

I have a professionally built ej22 frankenmotor (91 heads and ECU) in my vanagon

one of the nagging issues is a persistently low idle (~500rpm) causing an annoying rough idle and vibration, at ~700 rpm the engine is perfectly smooth.

I recently hooked up my AC which would occasionally make the problem worse by stalling the car. To my suprise i discovered that the builder already applied a 12v signal to the AC wire at the ECU in an attempt to raise the idle.. I have played around with the IACV as well as the air bypass screw and it runs perfect, but the ecu eventually re-learns and drops the idle back down. What other things should I try in order to solve this?

Welcome to the BBS.

Are you running the 91 Legacy ECU? Which IAC valve does your engine have? Is it the rotary valve or the reciprocating valve? Are you using the stock Vanagon tachometer to determine the idle? Have you tried to use a more accurate/external tachometer to determine/check idle speed? The reason I ask this is because on the stock Legacy dash the tachometer has a line that is commonly mistaken for 500 rpm when in fact it is 750 rpm.

Belated response...

I am running the corresponding ecu - the IAC is rotary style and I removed and cleaned it (to no avail). I am using the vanagon tach but feel good about the values since they seem to translate 1:1 and this conversion is very well tested and developed in the vanagon world... What would be the next thing to test?

My suggestion would be to try and build this scan tool so you can see what is exactly going on in the ECU, or if you have or know someone with a Subaru Select monitor to read the ECU...that would also work.

https://surrealmirage.com/vrg3/b10scan

Beyond that, you could try another ECU.