C.E.L CHALLENGE

Having problems solving P1505 and P0505 on a 2002 Honda CRV i even took it to a shop for assistance and they were also stumped so i will list below everything I've done and hopefully someone can help me out

2002 Honda CR-V (K24A1)

Idle Surge Diagnostic Summary

Primary Complaint

Idle surges between 1200–2000 RPMNo stalling when warmWhen IAC is unplugged (warm), idle drops and remains relatively stable (within ~100 RPM)Stored Codes

P0505 – Idle Control System MalfunctionP1505 – IAC Circuit Malfunction(No other active codes at this time)

Parts Replaced

OEM Idle Air Control Valve (IAC)Aftermarket IAC (tested as well)Throttle Position Sensor (brand new)EVAP purge valveKnock sensor (resolved prior code)Water Pump/ThermostatMAP SensorThrottle body gasketECM Test

ECM swapped with known good unitNo change in symptomMechanical Checks Performed

Throttle body thoroughly cleaned (plate + bore)Cooling system properly bled multiple timesBrake booster hose inspected (no leak)Throttle cable adjusted (no change)Throttle stop screw adjusted (no change in TPS reading or idle)Visual intake inspection completedElectrical Testing Performed

TPS Circuit (Unplugged – Key On)

5V reference: 5.05VSensor ground: 0.025VSignal (unloaded): 0.052VLive Data (Engine Running)

TPS reading: ~9.4% at closed throttleSTFT: ~0%LTFT: ~0%MAP KOEO: 91 kPaMAP at idle: fluctuates 37–50 kPaRPM fluctuates 1200–2000IAC Functional Test

With IAC unplugged warm:

Idle dropsRemains relatively steadyMajor surge disappears Indicates:

Base mechanical airflow appears stableECU is commanding oscillationWhat Has Effectively Been Ruled Out

Vacuum leak (fuel trims near zero)Intake manifold gasket (no lean indication)IAC failure (OEM installed and behavior confirmed)TPS sensor failure (replaced)ECM failure (swapped with no change)Cooling system air pocketEVAP purge stuck openKey Observations

Scanner shows 9.4% TPS at closed throttle.Mechanical airflow stabilizes when IAC is unplugged.MAP reading at idle is higher than expected (37–50 kPa vs expected ~28–35 kPa).Fuel trims do not indicate lean condition.Surge appears ECU-controlled rather than mechanical vacuum leak.Requested Focus for Shop

Rather than replacing additional parts, please verify:

Actual plugged-in TPS signal voltage at closed throttle.Sensor ground integrity under running load (voltage drop test).Base throttle plate seating and airflow.Harness integrity at shared sensor ground splice (TPS/MAP/ECT).Confirm IAC duty cycle behavior during surge event.Important Context

The vehicle has had extensive DIY diagnostic work performed.

The concern appears to be input signal interpretation rather than a basic air leak or failed actuator.