Hey everyone I recently swaped a d15b8 engine out of a CX into my DX civic that had a d15b7 motor in it. Everything worked just fine except for one issue, my idle bounces up and down when the car is at operating temperatures. it gos down to 800rpm back up to 1700rpm then back down then back up. Im not sure what the issue is. I think it may have to do with the diferent maf sensor locations and wires. The DX had the maf sensor on the firewall and the new motor has it on the throttle body. The car only runs if I attach the dx maf connector to the cx maf sensor. If its unplugged the car will not start at all. If you guys could give me any ideas that would be great. thanks in advace for any help you may have.

 

bleed your cooling system.
and there is no maf. its a map sensor.

 

oh sorry map sensor. I have tried to bleed the coolant system I didnt fix it. well actually i tried to bleed it twice any othe suggestions.

 

check your wiring. or which ever was different. between engines.... make sure you have your grounds......are they from the same year?

 

im not sure what year the new motor was from other than it was a 92-95 cx. The new wires go that came with the motor go to the egine wiring harness and then go no were past that. The old map sensor wires go directly to the ECU. I will check my grounds again though does the ECU have a ground wire in these cars?

 

As you said plug the map sensor connector coming directly from the ECU into the D15B8s throttle body map sensor. '92 - '93 DXs actually any '92 - '93 civic that came with a D15B7 uses a firewall mounted map sensor, '94 and '95 DXs use a throttle body map sensor like the D15B8 in the CX. both types use the same wiring and work more or less the same, throttle body is prefered though, should a little more accurate and theres no vaccum line to rot, get cut fall off, etc. For your issue i'd proabably guess the IACV was dirty.

 

fitv?

 

vacuum leak? too lazy to read the posts but i'll bet it's the problem

 

Also check to make sure you have the right ecu for the engine, because that could cause the idle to bounce

 

I got the ECU as part of the swap so I believe it is the right one. I have looked for air leaks and found nothis I will take of the IACV clean it and let you guys now.