Hello everyone, several months ago I swapped my 2005 Honda Civic 1.7 VTEC from an automatic transmission to a 5 speed manual and I have been having an idle problem ever since. When I am coasting, the RPM will usually not go down to an actual idle. Instead, the RPM usually hangs around 1000-1500 for no apparent reason although I have seen it go down to an actual idle a few times. There isn't much consistency to the high idle either. Sometimes turning on loads such as the AC will increase the idle, but sometimes the RPM will stay constant. The only consistent behavior is that the idle is always a perfect 700-800 RPM when I am stationary. Also, if I unplug the speed sensor so the ECU doesn't know the car is moving, the idle is always perfect.
I have the proper 5 speed ECU, proper IACV, no vacuum leaks, TPS reads idle. I also tried disconnecting and plugging off brake booster, PCV, and evap solenoid, but no luck yet. I swapped the IACV with an extra one I had just to try it, which as I expected didn't solve the issue. I did initially think I fixed it though since immediately after that the idle was a perfect 700-800 RPM the whole way to college the next day regardless of loads or speed, but it started acting up again on the way home. I have also tried with the alternator unplugged since I read it can cause a high idle if it is incorrectly reporting a high load to the ECU, but it made no difference.
I am starting to wonder if I have a defective ECU since the idle is so inconsistent while coasting. Seems somewhat unlikely since the car drives perfectly otherwise, but at this point I can't think of another explanation since the engine is obviously mechanically capable of idling properly if it wanted to.
If anyone has any other ideas please let me know. Thank you very much in advance!
I have the proper 5 speed ECU, proper IACV, no vacuum leaks, TPS reads idle. I also tried disconnecting and plugging off brake booster, PCV, and evap solenoid, but no luck yet. I swapped the IACV with an extra one I had just to try it, which as I expected didn't solve the issue. I did initially think I fixed it though since immediately after that the idle was a perfect 700-800 RPM the whole way to college the next day regardless of loads or speed, but it started acting up again on the way home. I have also tried with the alternator unplugged since I read it can cause a high idle if it is incorrectly reporting a high load to the ECU, but it made no difference.
I am starting to wonder if I have a defective ECU since the idle is so inconsistent while coasting. Seems somewhat unlikely since the car drives perfectly otherwise, but at this point I can't think of another explanation since the engine is obviously mechanically capable of idling properly if it wanted to.
If anyone has any other ideas please let me know. Thank you very much in advance!