Sterlinbubba

1998 Civic Coupe EX (swapped to manual)
Has the automatic engine harness still. Has ecu 37820-p2p-a84.
Codes that remain after clearing: P1509, P0141, P0700, P1758, P1768. I assume I can ignore the auto trans codes.

Ok, I am brand new to Honda ownership, I recently purchased a 1998 Civic EX with the D16y8 that was swapped to a manual transmission years ago from a coworker. I bought it to learn how to drive stick. After getting a feel for the clutch in my driveway, I took it on the road and discovered that it will rev fine up to just under 2000 rpm and then it will buck very harshly like a limp mode unless you press the throttle more. It does the same thing in neutral, like a weird 2 step. I am a Toyota technician and I have spent all day researching this car, the swap, and verified the throttle position sensor does not have a dead zone, checked for vacuum leaks.

Anyways, eventually I realized that the IACV had been swapped to the 2 terminal connector one. One terminal has 0 voltage with key on, and the other one has continuity to the pin that was swapped on the ecu connector. After taking my alligator clip off of that terminal, it fell out of the connector, it was poorly soldered.

My question is, would this concern of bucking at lower rpms likely be caused by P1509? I plan on fixing the ground wire to the ecu connector, but shouldn't the other terminal at the IACV have constant source voltage with the key on? I couldn't really find a diagram showing power flow to that terminal. I would really appreciate any and all help.

JRCivic1

ALL automatic P2P ECU's have a 3-wire IACV circuit. After your manual transmission swap, it sounds as if the intake manifold has been swapped and it now has the 2-wire IACV mounted on the back of the intake manifold. This will NOT work with the automatic ECU, and this is why you are experiencing the bucking at lower engine RPM's. Swapping out to a manual version ECU will, assuming the IACV is wired properly, fix your issue.