Hello, considering you have replaced the Air idle control valve, which are a huge problem on Honda's, it sounds like you may have a vacuum leak. Does the surging go away when you have your foot on the gas pedal and are at a higher Rpm? And the coolant fan shouldn't come on right at a cold start. Here's the Fan circuit below.
We usually use a smoke machine for vacuum leaks, but here's a guide for diagnosing a vacuum leak. We have limited wiring diagrams for a vehicle this old. but also try unplugging the purge valve and blocking off its tube to the intake manifold, do the same with the brake booster hose.
You can also check the MAP sensor, back probe the connector with your multimeter on the green/white wire and see if it changes when you press the gas pedal. A faulty Coolant temperature sensor or Intake air temperature sensor can cause surging on Honda's as well.
But if your raise the RPMs and the surging goes away, then you most likely have a vacuum leak and that's what you would want to check for next. Honda's main problem always seems to be surging issue. Let us know what you find.
https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge
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Monday, March 14th, 2022 AT 9:49 AM
