Just picked up a boosted 99 Civic with a d16y8. For some reason when the vehicle is warmed up when I am driving and put the car in neutral or press the clutch pedal in instead of the RPMs returning to idle (about 600 rpm) they go way down to almost 0 then bounce up to 600. When the car is stopped the same issue can be caused by reving the motor and letting the rpms drop while in neutral or clutch in and in gear. The car has a new fuel pump and injectors so I know its most likely not those causing the issues. There is one sensor that comes before the throttle body and intake manifold that usually connects to the connection between that and the intake housing that is not connected (there isnt anywhere on the tubing to connect it) and that sets of a CEL when I boost the car between 5k and 7k rpms but otherwise remains off. Not sure what that one is or what if it could cause the problem.

When I cold start the vehicle it has a higher idle like normal (around 1500) which eventually as the vehicle warms up lowers down to 600 where it will steadily sit.

Sofar only thing that has triggered the rpms dropping below idle(but always back up to it) is when the rpms are dropping from reasons stated.


Thanks in advance! Other than that issue and the fact that the car came on those ghetto coilover sleeve inserts I'm pretty happy with the car. Ordered a new suspension because those sleeve inserts ride like complete ******* ****. its a 99 Ex sedan with an si front end conversion Hopefully can fix this and be completely happy with it. Thanks

 

TPS sensor maybe? Possibly vacuum leak but I can't think of what would trigger it selectively based on what you said.

The car is turbo? What's the blow off valve setup on it?

A pic of the engine bay may not be a bad idea to provide.

 

from what i can tell its a full ebay kit. ill provide one when I can

 

And im going to fix the camber when my new springs and struts come in tuesday 😂😂😂
I know i need a wastegate dump pipe still. Working on that
Here's what she looks like right now. Going to clean it up once I get it running cherry.

 

need to get a dump tube
not sure if the sohc has a iacv. if so it could be dirty and just need some cleaning or it could be failing in which i think mine is doing in my gsr.

 

It may help if you bring your base idle up a bit. Im pretty sure factory specs call for it to idle around 750 ish so 600 may be a bit too low of an idle to begin with

 

Could it be the tune for my vehicle as well? My manager says that because when the car was tuned in winter when the air is colder or denser, and now it being summer with hot air that I might need a retune for the difference in air temperature? He says his NA car does the same thing about dropping below idle but his never stalls mine has a few times, but he has a winter and summer tune.

Also what sensor is it that I dont have plugged in? On a stock airbox it should be plugged in between the filter housing and the intake manifold.

 

No. that shouldn't be the case. Not if it's tuned well. The rest of the car's ECU functions should be able to adjust for humidity, barometric pressure, and temperature. More than likely, its an overly rich condition, or you just need to have the idle rpm above 800. It's not going to kill the car.
But, you need a dumptube before you can go driving anyway. I'm surprised you're tuned that way to begin with.