Great diagnostic work and write up Mark. If you are POSITIVE that the IAC is clean then I’d suggest a wire by wire check of the harness wires connecting the IAC to the ECU. That and more driving cycles to see if it recurs.?

I did have a vacuum leak on my 1999 Phase 1 2.5 which manifested itself with a wavering idle and failed smog checks (Oregon). Replaced every vacuum hose and a leaking Pressure Sources Switching Solenoid Valve and, Bobs your uncle, passed smog and idle settled down to expected behavior.?

On Apr 5, 2023, at 11:43 PM, Dr Mark <mark@...> wrote:

?Hi . im slowly breaking in my newly restored drive train ( 1994 AT 2.2 LEGACY OBD1? donor in a 86 syncro? westy) and after a 150 mile stretch all i got for codes was the normal AT neutral codes that neve affected me for 100k . startup (without touching the gas pedal0 always goes to 2k and gradually drops to 1.125k . Ill admit i did a ton of low mileage runs and diagnostic reads using evo scan an B10 . anyway that long run was great and motor is strong .. today i did a 20 mile highway run and as i came off the exit i got a rough running engine and a flashing check engine signal , my first thought was i had a plug wire come loose . pulled over let everything cool down (happened to be at costco so .. hotdog) . getting really used to reading the codes so i did. saw a code 24 . used my handy dandy code sheet I have taped on to the ECU. . .?
said?ECU turns off 1 or 2 injectors to reduce idle speed for certain RPMs, speed, and throttle?
OK explains rough running so i decide to wipe codes before opening the engine hatch. and voila no more code or rough running .. for me that's a worst case scenario . i donno what happened or why its "fixed" . got home no issues?

I have mentioned weird throttle position sensor readings here before but that never got much traction & i get good readings from it .
looking at my files i also see code 24? described as?

- Air control valve or circuit (exc. Justy); Idle speed control solenoid valve (Justy)

and?

Code 24

With the IAC code 24 thrown, the ECU will use what is called 'fuel cut' to reduce excessive engine RPM. It turns off 1 or 2 injectors to maintain idle speed, for certain values of RPM, vehicle speed, and throttle position. This can result in a rough idle, and poor idle exhaust emissions values.

Most often with the IAC code, the IAC valve just needs to be cleaned. These are the best resources I have found for IAC cleaning:

• 
  (Note: this last one is for the EJ20K engine, but has some good tips)

On some early EJ22s, there is an idle adjustment/air bypass screw on the intake body, which is used to adjust the idle air only to the point that the IAC duty cycle remains in range.

.now i know i will get the clean the IAC comment ..but i can tell you its clean .. can it be too clean ? i used california "organic" brake cleaner .. i can't see any way to lube anything . possibly just too old .. Probably 220k miles .?

i am suspicious of vacuum hoses ..but its a guess. does anyone have a lived experience to share . thanks .?

?m?

Hello,

I had a very similar issue ("when I came off the hwy into a short exit - heavy downshifting/high rpm's) and it turned out to be the vehicle speed sensor was not aligned properly after I had some mechanical repairs performed.

I performed the electrical test (wiring harness, AICV resistance, etc), cleaned then replaced the AICV, purge value, performed a smoke test, etc, etc.

When I went under the vehicle, there was 2-3" gap between the vehicle speed sensor and the sensing ring on the cv flange.

After proper adjustment 1/16", the issue was resolved.

Best,

Todd N-haus

On Fri, Apr 7, 2023 at 11:03?AM Brent Weide <brent.weide@...> wrote:

Great diagnostic work and write up Mark. If you are POSITIVE that the IAC is clean then I’d suggest a wire by wire check of the harness wires connecting the IAC to the ECU. That and more driving cycles to see if it recurs.?

I did have a vacuum leak on my 1999 Phase 1 2.5 which manifested itself with a wavering idle and failed smog checks (Oregon). Replaced every vacuum hose and a leaking Pressure Sources Switching Solenoid Valve and, Bobs your uncle, passed smog and idle settled down to expected behavior.?

On Apr 5, 2023, at 11:43 PM, Dr Mark <mark@...> wrote:

?Hi . im slowly breaking in my newly restored drive train ( 1994 AT 2.2 LEGACY OBD1? donor in a 86 syncro? westy) and after a 150 mile stretch all i got for codes was the normal AT neutral codes that neve affected me for 100k . startup (without touching the gas pedal0 always goes to 2k and gradually drops to 1.125k . Ill admit i did a ton of low mileage runs and diagnostic reads using evo scan an B10 . anyway that long run was great and motor is strong .. today i did a 20 mile highway run and as i came off the exit i got a rough running engine and a flashing check engine signal , my first thought was i had a plug wire come loose . pulled over let everything cool down (happened to be at costco so .. hotdog) . getting really used to reading the codes so i did. saw a code 24 . used my handy dandy code sheet I have taped on to the ECU. . .?
said?ECU turns off 1 or 2 injectors to reduce idle speed for certain RPMs, speed, and throttle?
OK explains rough running so i decide to wipe codes before opening the engine hatch. and voila no more code or rough running .. for me that's a worst case scenario . i donno what happened or why its "fixed" . got home no issues?

I have mentioned weird throttle position sensor readings here before but that never got much traction & i get good readings from it .
looking at my files i also see code 24? described as?

- Air control valve or circuit (exc. Justy); Idle speed control solenoid valve (Justy)

and?

Code 24

With the IAC code 24 thrown, the ECU will use what is called 'fuel cut' to reduce excessive engine RPM. It turns off 1 or 2 injectors to maintain idle speed, for certain values of RPM, vehicle speed, and throttle position. This can result in a rough idle, and poor idle exhaust emissions values.

Most often with the IAC code, the IAC valve just needs to be cleaned. These are the best resources I have found for IAC cleaning:

• 
  (Note: this last one is for the EJ20K engine, but has some good tips)

On some early EJ22s, there is an idle adjustment/air bypass screw on the intake body, which is used to adjust the idle air only to the point that the IAC duty cycle remains in range.

.now i know i will get the clean the IAC comment ..but i can tell you its clean .. can it be too clean ? i used california "organic" brake cleaner .. i can't see any way to lube anything . possibly just too old .. Probably 220k miles .?

i am suspicious of vacuum hoses ..but its a guess. does anyone have a lived experience to share . thanks .?

?m?

--

Todd Niedringhaus

267.275.5780

todd.niedringhaus@...

?