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Mechanical Problems/Vehicle Issues and Fix-it ForumIf you've got a problem you just can't figure out, a noise you can't diagnose, or a Check Engine Light that won't go away, ask about it here!
Hello,
I have a 1997 Honda Civic Dx with a d16y7 engine. It is throwing a p0401 code, which I have looked up, it is referring to an EGR valve. To my knowledge, this engine does not have an EGR valve. I have cleaned up the IACV pretty good, put it all together and still have idle surging after the car warms up. It jumps back and forth from 1k Rpm - 1.9k Rpm. Any thoughts?
is the engine original?
Is the ECM wrong? Check part number on the ECM (wiki says it would be P2E)
Is the code reader lying to you? (incorrectly displaying fault codes seems to be rather common)
On the surging at idle......When it's acting up, use your fingers to block the open port down inside the throttle body---the passage that leads to the IAC valve. If the idle comes down to something normal or tries to stall, that's a sign that the IAC is stuck open or being held open for some reason.
If it continues to surge with the ports blocked, look for external vacuum leaks.
is the engine original?
Is the ECM wrong? Check part number on the ECM (wiki says it would be P2E)
Is the code reader lying to you? (incorrectly displaying fault codes seems to be rather common)
On the surging at idle......When it's acting up, use your fingers to block the open port down inside the throttle body---the passage that leads to the IAC valve. If the idle comes down to something normal or tries to stall, that's a sign that the IAC is stuck open or being held open for some reason.
If it continues to surge with the ports blocked, look for external vacuum leaks.
The engine is original, everything on this vehicle is bone stock. Confirmed ECM is P2E. I don't know if my code reader is lying to me, I will ask it again but this time holding it over a cup of water . I will confirm by pulling the codes by jumping the computer and see how many times the CEL blinks.
To test the IACV with plugging the passage with my finger, do I have to open the throttle plate a little to get to the passage, or can this be done without moving the throttle plate?
Just checked the location of the ports, it does sit over the top of the throttle plate. I will do more testing tomorrow and inspect the vacuum lines once again if the problem persists. Thank you ezone!
Ok, I figured it out! I took apart the IACV once again, this time gave it real good cleaning. The idle surging is no longer there. I jumped the ECM and it threw a code 65 - secondary O2 heater sensor. I just replaced the secondary O2 sensor last week, so it was odd this was giving me issues. I took a multi meter and checked the voltage of the o2 sensor plugs from the wire harness - both the upstream and downstream plugs were identical voltages for the 4 wires it had. I then plugged the upstream o2 sensor into the downstream plug on the wire harness and vice versa for the downstream o2 sensor into the upstream plug on the wire harness. Plugged my code reader in and it was now throwing a P0135 - Upstream O2 sensor. Now i knew something was wrong with the wiring and I inspected a little more. I remembered when I was rebuilding the transmission, some wires came out of a plug and rewired it into the plug off a diagram online. I guess I wired it wrong. So I swapped out the upstream O2 sensor with my OLD downstream sensor and all codes have been cleared! I circled the little box where the wires have came off and my failed attempt to rewire them.
11-22-2017
. I will confirm by pulling the codes by jumping the computer and see how many times the CEL blinks. 
