1500 rpm idle

[phill]

Ok I searched and didn't find anything about this. Maybe I searched the wrong thing who knows.

I recently had a new engine put in my 1998 RS and now sometimes when I'm coming to a light and I drop it in neutral the rpms drop to 1000 and then climb to 1500 to 1700 until I come to a complete stop. Then drop to about 800 rpms. however It doesn't happen every time

I remember reading something about air in my cooling system so I ran it without the cap on for awhile in hopes of getting all the air out. It worked but then a few lights down the road it started again.

I have OBX rad. hoses, a 180 degree thermostat, and a 16 psi rad. cap.
the cap is a few psi stronger than oem and I thought that might have something to do with it.

Can you guys tell me what you think?

 

[Dsmj89]

Stuck thermostat, dirty fuel filter ? And how do you know for a fact your iac sensors are good ? Did you test them correctly ?

 

[phill]

I just installed a new 180 degree thermostat and it opens and closes fine. wouldn't the fuel filter cause it to stutter? Anyways I installed a Walbro pump w/ a new filter. and I ordered a new one from checker and tested it how the hayes book says to

 

[phill]

well so I turned that screw that adjusts the angle of the butterfly in the throttle body and it started to run fine. Just makes you realize how easy some of the fixes are.

 

[jdd1231]

My 93 nt does the opposite when Ive got the lights on and blower motor,it idles down to 700 or so,and even lower when the cooling fan kicks on.

It idles at about 1000 otherwise.....

Is there something thats supposed to boost the idle up when the system is loaded?

 

[cjridert1]

You checked for boost leaks - the system held 15psi? Let it idle high - step out and as someone said, make sure the TB plate is closed completely (TB cable can be improperly installed. Your idle switch either being bad or not being activated will cause this. The idle switch is that little dowel thing with the push button on the bottom that the TB arm will contact when it is closed. If this is not working, your rpms will be way above what you set. I had the same problem - check this out and let us know.

 

[phill]

ok so a while back I thought I fixed my idle problem but it turns out I really didn't. my car likes to trick me and make my life suck

Now I believe I have it all narrowed down to a vac. leak in the EVAP/emissions system. I was wondering if there was a way to figure out where its leaking from or if I'm going to have to replace every line in the damn thing.
I heard about a smoke test? or possible somebody had the same problem and could tell me where theirs was leaking from?

 

[stevo911]

IAC Motor ISC Motor whatever ya wanna call it.

 

[stevo911]

Sorry that was a reply for previous poster asking what revs the engine during load.

 

[phill]

as soon as any load is placed on the car like AC or lightly letting out the clutch it idles fine

 

[phill]

It also seems to not surge or idle high when its colder out, like under 90 degrees. So I replaced the IAT sensor and it didn't help either