idle drop when i use a/c Options

[99gt3sge]

ever since i swapped my 3sge in my sixth gen, the idle seems to drop below 900, there's times where the idle rises how its suppose to but then it drops again. i was wondering if any of you guys runing swaps have encounter this problem? could b my idle valve or is it controlled by the ecu?

[bsamps4]

Do you have you a/c vacuum switching valve connected to your intake and plenum?

[99gt3sge]

yes it conected, the hoses go to the plenum.

[Special_Edy]

yes it conected, the hoses go to the plenum.

Im not sure about the 3sgte but both the 7afe and the 5sfe have an 'AC Idle Up Control Valve'. It is located on the end of the intake manifold on the passenger side. I suppose the principle is exactly the same with boost as with n/a, you are just letting a small amount of air into the intake to compensate for the power used by the compressor. Mine went out and would sometimes stay open so that my idle would be way to high with the compressor off and then sometimes it wouldnt open at all and the idle would drop and get real rough with the compressor on. Replaced the valve and it fixed the problem. Though I had to get the valve at a salvage yard because there is not even a search term for idle up control valve at the autoparts stores. The dealership should be able to locate one though.

[trdproven]

thats what i was wondering too. for some reason, i see it on some online pics, but personally i have not found it on my 5s. i believe there is no screw, and it is computer controlled together with the IAC. if i'm right the screw is no longer there post 91.

This post has been edited by trdproven: Apr 19, 2012 - 12:15 AM

[Rusty]

idle at 900rpm seems a bit high?

[99gt3sge]

really to high at 900? what does yours idle at? ill try and figure it out this weekend.

[Syaoran]

I've been having my 5th gen idle at ~1000 RPM for a long while now. Nothing I can do to make it any lower. Haven't really checked for any vacuum leaks. I have the IACV unplugged and closed all the way because the coil seems to be bad (always trying to open the IACV) It really doesn't bother me. Mileage is affected but not by a whole lot, and since I've got mount inserts, the higher idle makes the car not rattle my teeth out...

By the BGB for our cars, our idle is 700 RPM +/- 50RPM if I'm not mistaken. Anything above 800 RPM is a "high idle".

[Special_Edy]

650 to 750 rpm is factory spec.

[trdproven]

just make sure your IAC is cleaned and operational before you start adjusting your idle.

[mkernz22]

My car idles around 1k to 1.1k lol probably because I added some more tension to the throttle cable since there was too much slack (at least in my mind). I like it though cause when it did idle around 750 - 800 (was always like that) the car would rattle and crap, and that annoyed me a lot

[Special_Edy]

well, you cant check the ignition timing with the idle like that
your shifting may be slower, because the throttle cant close as much
Significantly increased engine wear at startup
Reduced gas milage


and to mkernz22-
sounds like you have a misfire. The 95 wont show a misfire code like an OBDII. Pull the spark plug or injector wires one at a time with the engine running and listen to which cylinder drops the rpm the least when disconnected

[99gt3sge]

Well I found one of the VAc lines had a leak so I fixed that, and it worked for a bit but it started to idle low again and When I put the a/c it idles lower and dies at times. Any other idea's?

[ricochet1490]

the a/c bogs down on the motor. Think in terms of engery. to idle the car needs "X" amount of gasoline which equate to say... for instance 1200J of energy. That 1000 J is say, 150J for power steering, 400 J for the alternator and the minimum fuel needs for the motor are say 450J.... which of course equals 1000 of your 1200 available joules. At this point the motor is spinning freely and at whatever your stock idle is. Mine tends to be about 850 for normal operation. When the A/C turns on, it zaps the remaining 200 J of energy available at that fuel trim, which means the flywheel energy isn't as much because the A/C is using the other 200J.

Basically what I'm telling you is this. the A/C WILL and does on my 6g and likely everyone elses 6g, slow the motor rpms even though you are using the same if not more fuel to power the a/c. 900rpm while the car is on with the a/c is from my experience higher that usual, but maybe is necessary for a 3sge because of the lighter flywheel or smaller displacement or whatever. my A/C being on sets my idle to 700 or below and a little rough.

So I think you're fine.