Diagnosing high idle belived to be vacuum leak.
 

Trying to diagnose a high idle. Currently the engine idles at 1200 rpm. This is after replacing lim gasket and replacing twins to bnr stage 3 twins. I most likey did have some kind of boost leaks before the new twins but not sure about vacuum leaks as it never idled that high before. So now i have some questions after doing a smoke vacuum leak test. My Greddy smic is leaking quite a bit of smoke. Also have a coupler leaking smoke but what has me scratching my head is that I am getting a lot of smoke leaking from the metal plate that holds the tps. Also smoke from the what looks like the throttling body butterfly rod. Would this be normal to see smoke leaking from those areas (see pics with the smoke test) of those areas? Probably a stupid question but the coupler and intercooler leaking, would those be considered vacuum leaks or boost leaks? Thanks let me know what you guys think

Did you check the fast idle cam?

I belive the fast idle can was removed when I removed the thermal wax.

Only air leaks between the throttle body and motor can cause a high idle. Anything in front of the throttle body won't change the idle but can result in a boost leak which can lose power.

Looks like the double throttle was removed, did you get a block off plate for that? The block off needs a nice layer of RTV to seal up as well.

The fast idle cam being removed normally won't change the idle but if it's not done right the throttle will stick or not shut fully.

You can pull the TB off the car and shine a light behind the throttle plates, if you see light getting around the plates then they are cracked open and not sealing.

Dale

thanks Dale. I will remove the throttle body for further inspection and to verify that the block off plate is still sealed.

Anything else I should check out? I will be removing elbow and throttle body today for further inspection. Let me know if I should check anything prone to vacuum leaks or any other parts I should look at. Thanks

Dale just did the flash light test and I definitely get light threw all the plate edges. Does that make the throttle body bad or can that be fixed some how? I also did another smoke test without the throttle body and covered every opening and now I have no smoke leaks well other from the bad coupler I have. Also from the smic top bolt holes. I will just add rtv to those bolts and that should take care of that. Thanks

You should see no smoke around the throttle body/UIM (referring to your first post)

Seeing a little light around the sides can be OK, it's a gap at the top and bottom you're looking for. If there's a gap you can adjust the throttle stop to set the closing point on the throttle. Study the linkage, there's a jam nut and stop that an arm from the throttle hits. There's one for the primary and one for the secondary plates.

You can also, with the car running, pull the elbow and use your thumb to block off the tapered hole at the bottom of the inside of the throttle body. That's the port that goes to the ISC. If the car stalls, it's the ISC doing something it shouldn't be. If it keeps running, you have a leak past the throttle body.

Also make sure you aren't making the throttle cable too tight when you attach it, that can crack the TB open.

Since you just replaced the lower intake manifold gasket, there's a lot of things down there that can cause a leak. If the old gasket wasn't fully scraped off, if one of the vacuum lines to the LIM weren't reattached, and if the rubber seals at the base of the fuel rails weren't re-attached, you can have a leak. You can use starting fluid to find a leak down there, carefully spray the starting fluid down in there and the engine will rev up when it sucks the starting fluid in. If it does, you have a leak down there somewhere.

Dale

if I had a vacuum leak on the fuel rails or the lower intake weren't I be getting smoke leaks from them? Thanks Dale

The smoke may not be making its way that far down. The starting fluid method would work better in that it is obviously sucking air in, it will suck that fluid in and rev up.

At the end of the day a lot of it is just looking and going through everything. It doesn't take much of a leak to make a pretty substantial change in idle.

Dale

Dale i don't see how the smoke wouldn't make it down there. I am putting the moke threw the brake booster hose right where it hooks up to the upper intake manifold. I even get smoke to come out threw the turbos intakes. But will try starting fluid. Thanks

Bump

Dale already said everything that anyone else is going to say.

High idle possibilities in order are vacuum leak past TB, poor adjustment of TB screws, idle control valve, ECU/wiring.

If you have verified there is no vacuum leak then an idle of 1200 largely qualifies as who cares beyond that if everything else is in order.

I might get a little flack for saying this... but this is based on my personal experience and care taken when trouble shooting similar things.
If you carefully spray brake clean, ether, or similar aerosols around suspected vacuum leak areas... (while idling) the engine RPM will rise when sucked in.

So I carefully do this around flanges, bolts, and other areas that are metallic. (I've done this around other materials as well, but I wouldn't recommend it as you don't want to degrade the plastics/rubbers from the solvent.)

This technique helps me pin point trouble areas.

(Edit) Looks like Dale mentioned this too at the end of his post... See, I'm not crazy... :lol: