I've searched the forums and tried the various suggestions, but still having the issue. I'm hoping someone can nudge me toward the solution.

The vehicle is a 2002 Accord sedan with 3.0L V6. Has A/C. 206,000 miles on it. My daughter's car.

Work that has been done: The timing belt broke, some valves bent. I tore it down to the block and the heads went to the machine shop. I put it back together, new water pump, timing belt and tensioner, set the timing, adjusted valve lash, used new Felpro head bolts, Felpro gasket kit, so all new gaskets for heads, intake, plenum, valve covers, spark plug tube seals, throttle body, water passages, thermostat, EGR valve, IAT sensor gasket, injector O-rings upper both intake manifold and fuel rail. I also replaced the VTEC/Oil Filter adapter seal, crank position sensor, the power steering pump and high pressure hose. I reused the old PS pressure sensor. I cleaned carbon out of the upper plenum passages, since I had access to it.

• Issue: The car runs fine except for the surging idle. On cold start up it, idles high, and then when it warms up it begins to surge the idle up and down at an interval of about 3/4 to 1 second. Check engine light kicks on and scanner shows a P0505 code which my book points to the IACV. I cleaned the IACV and still had the problem. I replaced it with an after market unit, and still have the same problem.
• Engaging the A/C makes the idle normal. When the clutch kicks off on the compressor the idle surges again. Engage the clutch and idle is steady.
• I have checked for vacuum leaks to the best of my ability and do not believe there is one.
• I believe I have properly bleed the coolant system, but am open to suggestions.
• I have wiggled wires on the IACV, throttle body, EGR, and IAT connectors and so not get a change in behavior.
• Disconnecting the IAT sensor and running the engine causes a P0113 "Intake Air Temperature Sensor 1 Circuit High Bank 1". Reconnecting and clearing the code the circuit appears to be intact.
• Disconnecting the IACV connector makes the idle surge more quickly - close to 2 times per second. It throws code P1519 "IACV Circuit Failure". Reconnecting and the idle goes back to a slower surge - unless the AC is turned on.

From what I've read, the IACV receives inputs from other sensors, so I am wondering what else to check. Can the coolant sensor cause this behavior? The problem only happens when the car reaches normal operating temperatures, something is changing at that point. Also, why does running the A/C cause it to idle normal.

I'm hoping someone smarter than me can help me figure this thing out. The car was down for 4 months due to waiting on the machine shop.( Long story). I just need to get this solved so, I can get this thing back on the road.

Please let me know if you need more information to troubleshoot. I don't want to just through random parts at it without a good effort at diagnosis.

Thanks,
SD

 

Yes the coolant temp sensor can cause surging idle issues, that is usually why people say to ensure your cooling system is properly bled. If there is an air bubble next to the ECT sensor it can cause false readings. Therefore, if your sensor is bad or reading incorrectly it can cause an erratic idle.

Running the A/C changes the load on the engine and the ECU changes the ignition and fuel maps to compensate for that.

Unplug the ECT sensor and see if the erratic idle issue changes, for better or worse. It is the 2 wire temp sensor in the lower intake near the throttle body. IF there is a single wire temp sensor there, that is for the coolant temp gauge on the dash it does not have any effect on the engines operation.


by GhostAccord, on Flickr

 

Thank you for the suggestion. I unplugged the sensor, and the idle didn't really change, but it showed a voltage high on the circuit with the code reader. Reconnecting made the code go away after I cleared it. I will keep searching for vacuum leaks. I also changed the PCV valve, but that had no effect. However, pulling the PCV and plugging the vacuum line did steady the idle. So.... I'm still looking.

Any advice on bleeding the coolant would be appreciated. I followed what my Haynes manual said to do by leaving the cap off the radiator and keeping it topped off while the engine warmed up and ran for a while to get hot. Also, kept the overflow bottle tube submerged.

Thanks.

 

Finally got this resolved and passed emissions inspection. Not completely sure what fixed it. Never found a vacuum leak. Re-bled the cooling system multiple times with the funnel method and front end of car jacked up, and still had the issue. Took apart the old IACV and cleaned it again and swapped it back with the new one I had put on. Idle finally stabilized.

Thank you for all the suggestions.

SD