Just swapped the rooted motor out of sarahs old ZX, still having an idle problem misses and pops, drops down to 800rpm slutters sometimes down to 500 then picks back up to 1000 and idles perfect for 10 seconds, then does it all over again, i had exact same problem with old motor, the new motor is good goes well just idles like shit, i have swapped the AFM PTU ECU TPS Idle air intake valve. there is a unit next to idle air valve a square diaphram unit linked between the idle valve and centre of the balance pipe, nothing seems to change regardless of this being plugged in or not. what is its purpose? Modifications to drivetrain are HKS pod, single exit 4 inch exhaust 2.5 downpipes, no cat, EGR delete AIV delete PRVR delete PCV delete A/C removed, JDM 1991 2+2 n/a auto. opinions? i'm running out of ideas on this one.

what Spark plugs and ECU do u have on there ?

both are 21 number ECU's unsure off top of my head what plugs i put in. this one has the correct n/a iridium equivelants, the last motor had pzfr6b? is a number off the box that pops into my head, some ngk laser platinums

ok stock ECU then ...

plus are right

 

what i would check is the plastic Air intake pipes for cracks

and check all other Vac lines .. carbon caster side, and all others being controlled by little electronics

have a look over this hope it helps IDLE PROBLEMS 1 IDLE PROBLEMS 2

 

dan.:biggrin:

cheers for that mate, good to confirm some things.

 

i have bypassed everything, found a small airleak in a stuffed vac line, alot better now,, still feels down on power from the old motor, i suspect the lack of backprerssure in the new exhaust is giving me grief

idle has got a bit better now i ended up finding a vac leak... now the thing wont rev over 4k up hills and drinks gas, im suspecting cas adjustment, out with the timing light if the weather ever becomes nice again