2.3L ('83-'97) Bad idle, accelerating on own

[Camerondebusk]

1996 2.3, 5 speed single cab, 160k miles

Iac has been bugging me forever, holding a high idle, revving when clutch is pushed in. I’ve warrantied it with oriellys multiple times and the issue always comes back. Eventually wired in an inline switch routed to my dashboard where when flicked it interrupts power to iac and drops idle to 750(using anti diesel screw on warm engine). Iac is mostly used for warming up.

Recently however I’ve noticed the iac appears to be accelerating on its own at times(I can idle in second all day and don’t really start slowing down unless I turn iac off to kick engine braking in, it’s a noticeable deceleration immediately after pushing switch, or pushing brake pedal). Also am still having issues of when iac is on engine revs to 1.5k when clutch pressed and holds until at a dead stop, rpm’s also slow to drop making shifting a pain.

Possibly unrelated obd2 now intermittently reads 35-40% at idle, usually at 24-29, regardless of iac on or off. No clear cause.

Also also intermittent surging vibrations at idle, with no real rpm fluctuations or other signs of vac leak, almost like something is putting a load on engine then toggling off.

So far my main culprits are battery(2020 battery, good voltage, probably on its way out might be causing alternator load), egr(solenoid is new, running on 89, pings on 87, need to do the cavuum line test on valve), or tps sensor(oriellys part, reads 14% at no throttle)

Any input would be greatly appreciated

Maintenance is fairly up to date, ignition parts are new, new fuel filter, fuel cleaner ran, injectors are oem, maf cleaned, filter 6mths ago, seafoam intake spray. No ac, no power steering

 

[franklin2]

What happens if you turn the switch off that you installed on a warm engine, and instead of setting the idle rpm at 750, set it at 500 with the idle stop screw? The IAC may want to add a little bit, even after warm-up.

 

[SenorNoob]

I agree. IAC likely has a minimum power above zero.

 

[Camerondebusk]

I’ll try that when I take er’ out today.

 

[Camerondebusk]

What happens if you turn the switch off that you installed on a warm engine, and instead of setting the idle rpm at 750, set it at 500 with the idle stop screw? The IAC may want to add a little bit, even after warm-up.

rpms now surge at idle and fluctuate between 600 and 900

 

[franklin2]

rpms now surge at idle and fluctuate between 600 and 900

You may be getting somewhere. Two ways to go. You can leave it alone for a few days, each time you make a change with this system it takes a few start and stops for it learn the new settings. If you still have the surging, I would lower the rpm with the IAC unplugged to 400 or lower. So the engine till runs when warmed up with the IAC off, but barely without stalling.