Another sr20 problem i know....

[burgessn]

Ok boys I need some major help from the sr20 gods. It's kinda hard to explain so bare with me. So when I start the car (cold engine) it idles very rough and lumpy but it is a stable idle at around 1100 rpm. And my afr is Suuuper lean at 22.5 if I give it a little gas it will clear up and start idling normal at 14.5 and the lumpyness goes away. Also worth mentioning to get it to idle at 14.5 and down around 1000rpm I have to turn the screw on the iacv all the way down clockwise. Also it doesn't always fix it's self in the first rev sometimes it takes 3 or 4 times to get it to act right. Please someone help me figure this out.
Specs:
Fully built sr20
Hx35 with z32 maf
850cc injectors
Fpr set at 43 at idle
Rs Enthalpy tunned ecu for 113 race gas

Let me know if you guys need anymore info.

[cotbu]

You have a vacuum leak, and you'll probably need to redo timing and base idle.

Here's a test, make sure the throttle plate is fully closed,,start the engine and clamp off the iacv hose completely if you don't stall, the leak is considered big. If you clamp off the pvc line the engine should idle lower also confirming a leak somewhere. Boost leak test or smoke test to find the leaks, no brake cleaner when you're idling over 1krpm.

Before you do any of those things pull codes at least, could also have a faulty mafs etc.

Sent from a Highly Tuned Note 4.5!!!

[burgessn]

Ok I'll give that a try and see what I can find. I'm just a bit confused how a vacuum leak would cause this? If it was a vacume leak why it clear up just by giving it a little gas. Wouldn't a vacume leak be present at all times

[cotbu]

It really depends where the leak is, and it could be multiple issues you have, like a stuck dirty iacv, or no coolant to the iacv or a bad mafs. The ecu tries to compensate for most issues so you probably were driving it like that for a while and the timing changed so you don't bang it to death, then the ecu gave you visual clues like bouncing tach, and rhythmic idle. These are just guesses based on what you describe. I could tell you every scenario with every possible cause, but that's ridiculous. You have to get in there and narrow the field so it becomes more clear for I and or other techs.
As we start to rule out things, others may reply about what they think it is based on what it's not or what you find. My goal is to make every 240sx in the world work like it's supposed too, but the owners... that's the challenge. ;) XD!

Sent from a Highly Tuned Note 4.5!!!

[Kingtal0n]

you say fully built sr? And you have 113 in the tank? I think you should not be worried about the quality if your idle. Do a boost leak test is about the only really important thing you should do.

if you had a stock engine i would say it sounds like your iacv is getting stuck. So change it I guess. But with 113 in the tank and who knows what sort of cam and compression ratio...