89 240sx KA24e engine stalls when oil cap is removed

[L.D. 100]

Ive already took the head to the machine shop and had it all looked through, I was told everything was fine. were else should I look? engine idles (crappy) revs fine but when I release the throttle it idles like hell again (not consistent, studdering, wants to stall) and when I take off the oil cap BAM! it dies... its really confusing me any help will be appreciated

[Silvia2NR]

Positive crankcase ventilation. Thats pretty much normal. The engine sucks back in crankcase blowby gasses by way of the PCV valve. If your idle is as bad as you claim, remove the IACV unit and clean it. Replace the PCV valve.

[L.D. 100]

Positive crankcase ventilation. Thats pretty much normal. The engine sucks back in crankcase blowby gasses by way of the PCV valve. If your idle is as bad as you claim, remove the IACV unit and clean it. Replace the PCV valve.

I hope this is it! this stuff is cheap just making sure, the IACV is that black box next to the exhaust manifold, infront of the MC?
Modified by L.D. 100 at 2:08 PM 1/31/2006

[AZhitman]

No. The IACV is under the upper intake plenum...

There's a good writeup on it here: zerothread?id=109345.

[L.D. 100]

ok found it (lol its even labeled "AAC Valve") how do I clean it?

[Silvia2NR]

remove it and clean it with throttle body cleaner. you will need to use a liquid gaket to put it back on. If you can find a vacuum hose that runs into it, try spraying TB cleaner into the hose and let it sit, start the car, you may have to gas it for it to run...keep repeating that and see if there are any changes in the idle..it's a worth a shot before removing the iacv.

[Ni2s4s0aSnX]

No, that black box is connected to the AIV. The AAC and IAA units are on the back of the upper intake manifold.

[Ni2s4s0aSnX]

But its a ***** to get off without removing the entire upper intake manifold. Because the screws are long and the fuel lines are in the way. And its impossible to reseal it without taking it off. Trust me, I've took mine off to clean it and ****, and I still haven't found the time to finish putting it back together so my 240 has just been sitting in the garage. It sucks. Definately not a job for a rookie.

[L.D. 100]

ok so I replaced the pcv valve, and removed the aac valve cleaned it all out and everything... and I still got the same issue. I pressed on the diaphram part of the egr valve to check it out and it seems to work fine, but then I noticed the idle got slightly better and the engine stopped stalling once the oil cap was removed. coincidence? does the egr valve have anything to do with this? could this also be removed and cleaned?

[rsmithdrift]

Sounds like you need to check your codes and check for vacuum leaks around the egr valve.