3Y-EU high idle

[apope]

My 1991 MasterAce Surf with the 3Y-EU engine has about 110,000 kilometers. After sitting for about three weeks in early February, the battery died. I jump-started it, and since then, it has had a high idle issue, running around 1,700–2,000 RPM. It still runs and drives fine, but the high idle isn’t ideal.


I checked for vacuum leaks around the top of the engine but didn’t find any. I also inspected the throttle body and intake, but they were spotless. My next step was to check and clean the IAC, but I’m unsure of its location on this engine. Aside from the throttle body, I don’t see any component with both a vacuum line AND an electrical connector.


I’ve attached a video of the engine idling for reference. Any help/tips in diagnosing this will be greatly appreciated!

https://imgur.com/a/OKZfLUd

[Jan-Willem]

If the voltage of the battery is low, a car idles higher to charge it. Have you checked the battery voltage now, when the van not running? A properly charged battery should be about 13v when you have just shut the engine off, to about 12.6v after an hour or so. If it is substantially lower than that, maybe the battery got damaged when it was discharged too much.

[apope]

Voltage checked out to be good and I went over the vacuum lines again including the brake booster. I did find that adjusting this white plastic screw on the intake decreased the idle as did disconnecting this sensor circled in red. What exactly are these?


1322713228

[originalkwyjibo]

Perhaps newer cars have the ability to increase idle for low voltage conditions, but that is not the case for our old vans. The vacuum lines and diaphragms you are referencing are part of the a/c idle-up system. I believe it may also be used for the hot soak pressure-up circuit as well. The "sensor" is a Vacuum Switching Valve or VSV and the diaphragm with the large white plastic screw should only affect the high idle speed when the idle-up system is active. It sounds like your idle-up maybe active which would explain the high idle.

[originalkwyjibo]

In watching your video again I see your coolant temp is very low. High idle would be normal at low coolant temps. Does it idle high when warm?
I would also check for codes and check the TPS.