Runs Great, But Rough Idle????

[nissan240sx95]

hey fellas! new problem for u guys to save me with.... just bought a 93 nissan 240sx convertible...the car had a 96 240sx se engine swapped into it. when i bought it the car ran pretty bad....so i gave it new wires, ngk plugs, dis cap, ignition rotor, oil and bosch filter, air filter, fuel filter, transmission filter and flush, new coolant, tempeture switch and sensor. The car now shifts great and drives fine, but at idle or dropping in rpms to idle, the car runs real rough. it jumps between 400 and 700 rpms, and turning on the ac doenst change it at all. when i drop it into neutral it jumps up to 800 rpms, but then after about 30 seconds, starts idling rough again.

ive checked each wire for spark and they are all sparking, i disconnected the wires to each injector and the cars idle worsened equally on each cylinder. I cleaned my MAf and the idling issue dissapeared for about 20 min, then started up again. I had a friend recommend i disconnect the MAf and look for a change but i see little to no change in the idle. yesterday i did a compression test. results from 1-4 are 150,150,120, and 150. < is that bad, could that be my issue? any ideas? ive heard everything from advanced vacuum leak, to coil pack, to knock sensor, to distrbutor, to ecm, pcv valve, iacv, and even ignition control module.... does anyone know how to test these or rule them out? all are pretty expensive parts except for the pcv valve which apparently is a b**** to change.... any help would be greatly appreciatted.

[steve s14]

My guess is that you have a vacuum leak.

[Azrial]

dunno if this works for 240s but it does for gm's try retraining the computer for idle. disconnect the battery for awhile. Then make sure everything is of radio heat a/c etc. Then reconnect the battery and let the car idle until the fans kick on. Then turn the car off after it heats up enough for the fans to kick on. Then check and see if the car starts running right. On gm cars you have to reteach them idle anytime you disconnect the battery. Which I assume you did when you tuned it up. I would try it at worse it costs you nothing but time and the bit of gas you burn up while it idles.