someone please help

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iam sure everyone has helped on this subject and ive done just about everything i know. heres the problem, i have a rb20det and the idle is at 3k no matter the temp. the mint. i disconnect the iac the idle drops to the normal rpm which means the iac works. i fixxed a vacuum leak and now the vacuum on the boost gauge reads 20 in. so thats a plus but the idle is still the same? any ideas? i thought maybe the temp sensor sense it does affect idle? this has been eating at me for 2 months now and i dont know where else to take it. anyone please any suggestions?

[d356bud]

Did this high idle happen after you did something to the car? (ex: install a Q45 throttle body)

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no, everything is stock, the mintue i got the car runing it has been at a high idle.. i had a vacuum leak at one point the vacuum on the boost gauge was at 12.. its not easy to describe where it was at but ill try anyways. where the iac gets the vacuum or pressure, where it Ts off well you have the main line coming off the intake going to the T one side goes to the iac and the other runs in the valley beside the injectors that vacuum line goes to what looks like a box and after that goes under the throttle body to the intake plenum. it was leaking at the connection going to that box. the hard vacuum line was dry rotted and cracked. replaced that and the issue is still there.. maybe redo all the vacuum lines? and hope thats the cause?

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oh one more thing, i can touch the wires, connection going to the tps and it changes the way the car runs ( with the tps connected ) it spits when i jiggle the connection although that didnt change the idle

[MyFlySkylineGTR R32]

Check All Your Seals (ex. exhaust manifold,intake manifold) Last Time i worked on a 20 and the idle was high the intake manifold bolts were not tightened correctly. Try that.

[ItzGenX]

If there's enough air to "idle" at 3k... wow that sounds like a huge vac leak if there is one. I would make sure to completely rule out the IACV by blocking it's air supply while the engine is running. If the engine stays running (after warmed) then it would be a huge vac leak. If it dies, well maybe you can blame your IACV. Just because you unplug the IACV to drop the idle, doesn't mean it's working properly. Also you might want to look at your throttle body fully closed stopper. It may need to be adjusted. There is also an adjustment screw on the IACV itself that may be set too wide. It could even be the TPS needs adjusting.

[Gabes13]

Put a multi meter to the tps and acc unit. What are the readings? Make sure all your intercooler pipes are tightened down good.

[RustspecS13]

I helped a friend with an SR20 like that.

Check and make sure the throttle body isn't being held open by the stop screw. A tab next to where the throttle cable goes will stop on a screw that's molded into the throttle body housing. If that is cracking open the throttle AND the IACV is trying to still add air for an idle, its easy to get it up to 2200-3000rpm.

There is also a vac line that needs to be blocked off on the underside of the t/b. East to miss.

~Alex

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ive herd multiple times about the line under the throttle body that needs to be blocked off.. how big of a line is this? i am going to make this easy i hope, i am doing a smoke test tomorrow on it and see if i can get some type of leak. i havent tryed the throttle body screw yet. i never thought about that. ill take a look at it tomorrow. oh i can hold boost all day thats the other werid thing.. i did try blocking the air off to the iac and it killed the car instintly.

[Gabes13]

The line that's under the throttle body is a pre throttle body vacuum source that originally goes to the charcoal canister. If you're not running one, block it off. I dont know the exact diameter but it's about the same as the other 2 vacuum sources on the manifold.

Directly under the throttle body, tucked under the plenum (POST throttle plate) is a large vacuum source for the cold start valve. The hose is small in length, but is prone to cracks or tears.

[Powered Bya Skyline]

does that cold start box tap into the iacv vacuum source?

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well decent news, i did a smoke test to the manny and i found about 3 leaks, one from the nipple for the brake booster and the stock boost gauge nipple, along wth a small nipple under the throttle body that goes to the charcoal cansister that i dont have, and the pcv hose. i also blocked off the what i am guessing to be the cold start box? i could block off the iacv before and the car would stay running, once i blocked the other line off not so much. heres the werid thing after fixxing those problems i still had an above normal idle say around 23 to 2500 rpms on my doch tach. i know its higher than what it actually is but once i disconnect the iacv the idle drops to around 1k on the tach and it idles amazing, any ideas? maybe anther vacuum leak i missed?

[Cjmartz2k]

How far out is your IAC valve adjusted?

[StricNyne]

is your tach calibrated ? lol or are you using electronic monitoring

[Gabes13]

does that cold start box tap into the iacv vacuum source?

Yes. That chubby hose that's on the "cross over" pipe goes to the cold start and the acc unit. Then from the cold start unit, a short stubby line feeds to a hole in the plenum, just after the throttle body.

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the iacv adjustment is almost fully closed ( screwed in ). on the cold start box, i blocked it off at the T not at that manifold. i might have a leak somewhere in the line or box. ill have to completly take the box out of the car. ill have to try adjusting the iacv and see where it sets from there.

[Powered Bya Skyline]

ihaven calibrated the tach but when i bought the car the tach was pulled out of the dash, the guy screwed up everything so i know its not right and plain on getting a aftermarket tach. the car seems like its idleing a little high if i had to take a guess i would say 1500, when i pull that connector on the iacv the idle drops to what sounds like 750 900 rpms.

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i havent calibrated the tach but when i bought the car the tach was pulled out of the dash, the guy screwed up everything so i know its not right and plain on getting a aftermarket tach. the car seems like its idleing a little high if i had to take a guess i would say 1500, when i pull that connector on the iacv the idle drops to what sounds like 750 900 rpms.

[driftkid83]

You need to get a six cylinder tach your tach is reading to high because its meant for a 4 cylinder. Its going to read incorrectly until you do.

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the tach is the least of my worries.. if the idle is suppose to be at 750 or even 900 rpms then and the tach reads 1200 it wont matter but the mintue i connect the iacv back up the idle jumps to 2500 according to the doch tach.. it sounds like its around 1500 rpms. if it idles with the iacv disconnected to what sounds 900 rpms max, thats the problem. the tach i will get fixxed once the car runs right. the whole cluster to be honest is junk. the temp gauge doesnt work properly and ill be driving the car and randomly everything will stop working.. all the lights in the cluster and such. what all do you have to wire in the dash when you do the rb swaps? unfornetlly i didnt do the swap all i did was the lower harness so the upper engine harness i have no clue what to do or what was done. any help would be greatly appreciated

[StricNyne]

how do u know the idle rpm ? it sounds like you have a leak from the intake i had one and i idle at 2500, or u have a bad iac, even unplug the AC part on the IAC and see if that helps you out too

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its just a guess.. i dont know for sure what the idle is. iam in the process of getting gaugs and so forth. what do you mean by the ac part of the iacv? the only part i know of is the connecter and the vacuum source.

[StricNyne]

there is 2 conenctors, one for normal operation, and th epurple ( i think) is when u use ac and it gives more air to compensate, did u also try unplug the maf ?

[Carl H]

you really need to get a functioning tach so we can help you diagnose the problem accurately...some things ARE rpm dependent.

aside from fixing leaks you need to make sure the idle switch is engaging on the tps.
it could be not engaging due to a number of things such as:

throttle cable too tight - keeping tb blade open
improperly set tps
bad wiring
improperly set throttle stop

I would first check the throttle cable for binding then check the tps was set correctly...even simply unplugging the harness seems to be enough to nudge it out of calibration.

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tomorrow i will hopefully get a obd scanner which will give me the rpms and so forth and ill be able to give you guys all the information tomorrow for you

[ItzGenX]

I think it's a bit silly that you are trying to diagnose an idle issue without so much as a working tach. Basing the RPM on sound is not even going to be very accurate. Engines in general do not even sound the same as another. An I-6 vs I-4 vs V6 will all have a different sound due to the amount of combustions per cycle and how offset each said combustion takes place in the cycle. You NEED a working tach, inductive timing light with rpm readout, or an EMS readout. I understand if the idle may sound high, but it would probably be best to get a tach working first in order to see how off the idle really is and go from there.

[Yellow4g63]

the scanner isn't going to work unless you wired up a consult plug when u did the swap. Some timing guns will show rpm so u can prob use that.

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well today is what i got.. i checked everything over again just to make sure i didnt miss anything. the tps voltage was extremly high. 13v i adjusted it to .5 at closed throttle and the pitch of the engine dropped to what sounded right.. i know i need a tach and iam working on that. money is tight and getting a tach is just a matter of time. i believe i still have a small vacuum leak but its not horrable.. the gauge is reading 17 18 in. of mercury now. where is was at around 15. i still have some small things wrong with the vechile like the gauges and lights will work perfectly fine and everything untill i hit a bump or turn right, or if i get on the car and do a quick shift they will like turn on and off.. kinda like theres a loose ground, ill have to go over everything and double check it.