d15z1 to b18c1 jdm gsr idle issues


Junior Member
Ok well Im not even sure im in the right section but this is definatley a technical issue so lets get started.first off let me tell you what we used and modified.
He had the vx harness and the jdm gsr harness. We decided to use the vx because the orientation for the US specification were correct in difference to the jdm one which the shock tower plugs were backward.

First off mechanically what was replaced was the clutch kit. and valve cover gasket. We had some overzealous friends helping that decided it was alright not to change the water pump and timing chain but it seemed as though the timing belt was practically brand new no irregular wear on the belt just a few rust surface areas which were small to say the least. So after trying to get the nut off the crank 10 tools later. We mostly opted to avoid it at this time. We put a new gasket on the throttle body. Although it was not the vtech gasket we shaved it to fit the enlarged throttle size. I might be regretting this later on but it didnt completely fit the mating surface although we shaved it to fit the openings. We put new wires and NGK plugs. Most everything that is new was sourced off a 94-95 usdm gsr so maybe the gaps are different on the plugs? I doubt it but its always a possiblity. We put in a usdm gsr rotor for the distributor and a new distributor cap.

I did alot of the wiring but I might have missed some stuff basically we follow relic1 through our setup and he reccomended on how to accomplish stuff. Im assuming that the d15 had no knock sensor so we ended up having to wire for it. We took that wire pink/blue I believe and had to place it on the D3 (c3) location for the ECU. Relic told us that the d3 location was unused now on the conversion so to directly wire it to the location of the white wire on the c129 plug at the shock tower which turns blue/green to the ECU. No problem we pulled the white wire and put in the knock sensor wire in its place which directly routes to d3 on the ECU wow that was easy. Relic also related to us to use a mini fuse bocx and wire it to the power side on the battery post with a 7.5 fuse in it to protect it from a fire. Now we accidently broke the Evap purge selanoid wire at a20 which wasnt used anymore so we couldnt use that wire to put it in at a17 for the IAB or secondary intake setup. So on Relic's redout the D8 wire at the ECU wasnt being used anymore no problem we plucked the D8 out and put it in at a17 for the IAB on the JDM GSR which was a blue/white wire. We then traced it to the shock tower which was at plug c129 and from the vx harness pulled the blue/white wire and placed the IAB red/blue (not sure of color) wire in at its place to complete the connection. We also cut the plugs for the o2 sensors off and put the 94 USDM o2 sensor and mated it with the VX harness o2 sensor plug. We asked Relic what wires would mate with what so we could wire that correctly. So far so good we put the bad boy in and ready to start it the starter had been sitting for awhile so I had to tap it pretty good with a hammer while her tried to crank it to turn the engine over. It starts! YESSSA! We do have engine codes of course.

Well we look at the engine and its ideling at 2000 rpm wow. Pretty damn high. Our main problem right now is getting it back down to 700-800. I read a couple of posts about how a bad throttle gasket or not the right one could cause it to idel high. Also our idle on the throttle wire was set to its lowest setting. Our timing was way off. We moved it down but its still off. I believe the USDM one is 16B from TDC. We rotated the distributor towards the front of the car bay and the lines almost match up. Which leads me to believe that the distributor is off gear. But its only a 1/4 inch off. So for the engine to go from 1500 to 800 in a 1/4 inch difference would be phenominal. Which also leads me to believe that the timing isnt the only issue. My dad told me it could be a Vaccum issue I havent checked them yet but I will. Also he said it might be the fact that the car is bumped up in idle for A/C and that there might be another location to drop the idle. I read something about a screw near the throttle body. But I need more info on that one.

Also we broke the Knock sensor the the JDM GSR we soldered it back together on the inside and super glued the plug back on but im not sure if that thing even works now. Would that affect idle?

So basically right now our main issues are that of ( Idle needs to be dropped from 1500 to 700-800, Was curious if there was any other wiring that needs to be done that I overlooked utilizing the vx harness and the GSR ECU.) Wiring is a big issue for me cause I handled most of it. I just need to know if there are any other plugs for stuff in the ECU that dont line up from the VX harness to the GSR. Any help would be greatly appreciated.

Also Im a big nissan guy just helping a bud drop his Honda b in.


Senior Member
Well sounds like a vacume leak here is a easy wayt to find out. Get a can a break cleaner and with the engine running spray the break cleaner over all possiable places there could be a leak. You will hear a difference in the idle as soon as some of the break cleaner is sucked into the manifold. Do this with the engine cool and bee carful not to use to much break cleaner as it is flamable which makes this work. This is just a quick way to find a leak