RPMs dropping quick when clutch in on decel

[akana1723]

Problem is as the title says..

Just recently this has started to happen. When I am driving (particularly at higher rpm) and want to put the car into neutral to coast or downshift.. The rpms drop very quickly down to around 400rpm to where the car wants to stall, then catches itself and the rpms will float around a bit then go back to normal at idle. It has; however, stalled a few times because of this. It seemed that this just started last week right after I removed the hose from the discharge on the stock blow off valve and capped the nipple for the hose on the intake. I am not sure why or how this would cause my problem? I know the stock bov is a pos and it is being replaced by a greddy type-s... But still confuses me as to why I am having this problem after removing that hose.

Before this problem arose though.. I had another very intermittent issue that occurs only when I start the car... Start it up, and the rpms will hit about 1200 and then drop and almost stall or stall the car. Happens a few times and then goes away. Not sure if these problems are connected since this was happening way before the first problem.

I have not had a chance to look into it much yet but I am leaning towards a possibly dirty or faulty iac motor or a fuel filter. Any other suggestions?

Really appreciate the help!

 

[LiquidX]

If you recirculate your BOV as you are supposed to then you won't have this issue.

As for the second issue, have you taken the time to test the iac coils?

 

[AlaskanDsm]

Unless you have a MAF-T or some other meter AFTER the BOV, you can't run the BOV open to atmospehere as our cars are designed to RECIRCULATE the BOV back to the intake. That is the reason why you would be stalling and having the idle issues.

As far as other idle issues, I would start with a BLT
(http://www.vfaq.com/mods/ICtester.html) and verify that you have no leaks and your ISC is operating properly.
http://www.youtube.com/watch?v=l7R3gf7SiAo

All else fails, give this a look over.
http://www.dsm.org/how-tos/tttt/tttt3.html

 

[akana1723]

Hmm.. definitely did not know that. I have dealt with many turbo cars but this one is the first I have had with an MAF and a need to recirculate the BOV back to the intake. I am quite new to DSMs and cars using an MAF.

I guess I kind of shot myself in the foot on that one

As for the other issue... I will test the IAC out and see what happens..

Thanks guys

 

[tenn-gsx]

Also if you bov is weak it could be opening under vacuume conditions found during idle. This will suck air into your intake through the bov bypassing your maf causing your car to idle irratically since your engine is recieving unmetered air.