I swapped a rb20det in my 280zx. i have a wiring specialties harness,fmic,rb25 turbo, new rb20 maf, 12pound flywheel,spec 3 clutch, fpr,new plugs, aftermarket intake.....maybe missing a few items. My problem is when the car is at an idle and you give it the gas it drops rpms for a sec or 2 then revs. The rpms drop quick and if its already revd up alittle then it doesnt hesitate. but at an idle it does and wehen your next to the intake it makes a odd sucking noise when it does hesitate. Also when you first start it you have to give it throttle or it will just crank (try to start but wont).iv been having some problems with the idle dropping randomly to 400-500 and acting like its wanting to die and sometimes it does then it will kick its self back up and idle fine for 30 sec and drop down again. I started it yestarday tho and idled fine the whole time so i dont know. I put the fpr on since my plugs were really lean and after it feels like i hit a wall at 4k rpms.My ecu reads 55 so im not sure.......any help would be great thanks

You might have better luck posting in the RB forum as most of us in the classic section have little to no experience with the RB. That being said I do have a lot of experience with OBD0 and OBD1 Nissan injection systems. First off on any fuel injected car you should never have to touch the throttle until it's started unless there is something wrong. I'd have a good long look at all the electrical connections, take them apart clean and replug everything, look especially hard at the TB, CAS, MAF, CTS and PTU. Most of the problems originate from one of these sources and it's quite possible you have more than one issue at hand, next up clean the IACV, it's pretty common on just about all models to get dirty and stick. Next Check the ecu for codes, granted these older systems don't always throw the code they should but it's still a good place to start. I hope some of this helps.

Thank you for the response. I did clean the iacv when i swapped intakes....dont know how clean i got it but i did clean it. i checked the ecu for codes and it came back with 55 which mean all is ok. But something is def wrong to me acts like timing but iv checked it and seems fine. i unplugged my tps and the plug coming out of it and nothing changes while the car is running dont know if that means anything or not

The car starts fine but the idle drops randomly then surges back or occasionally dies? I'd have the iacv off and clean the crap out of it, sounds like it's sticking. also an improperly adjusted TB can cause the iacv to work overtime. It is possible that you have a slight miss like bad valve seat causing unburnt fuel to enter the exhaust O2 gets wonky and duty cycles get cut. But the iacv is the more likely issue.