Eyal 951

I've got the head on the caar for a month or so now, its got all new vacuum lines and hoses, but it had a leak. My zeitronix showed about -13.0 - -14.0 when cold, and maybe -15.0 to -16.0 when warm at idle. the idle was around 1000 rpm, but after some rpms it would stay at slmost 1100 before settling at 1000 rpm. I bought a 2 inch pipe end cap with a hose clamp, drilled a hole and put a valve stem through it, then i pressurized it with a compressor. you could easily hear the air leaking, and it would equalize itself to atmosphere within 8 seconds, 10 max. With a hose as a stethascope, I pinpointed the Idle stabalizer valve, so I pulled it out and tested it (blowing into it and covering the other hole, hey it works) even with the maybe 1 psi i can generate with my mount, air escaped pretty quick. I sealed it up with jb weld, retested and it didnt leak. I installed it and put it back together. Starting up the car, my vac numbers are the same (-13.0), then the idle stays around 1200. i let it warm up, and the idle was about 1200 to 1250 or so, but held pretty steady I figured maybe I have to re-adjust the TB, since i adjusted the idle down before when the ISV was leaking. I went out and had a few WOT pulls in the first three gears. it seams to pull a bit better then before, but thats not for sure... though I did get some wheel spin in first in a place I never have before. but when i let off, and let it idle, it went down to 1300 idle for a second, then cut the injectors down to maybe 900 and climbs back up to 1300 and repeats. (hunting idle) my vacuum numbers arent any better, but no worse then before. After installing the ISV i pressurized the system, and it heald pretty well. at 12 psi, it lost 1 psi per 15-20 seconds or so.
Sorry for the long winded post, but I'm out of ideas, I need advice. Could the Idle Stabalizer Valve be bad? TPS? TB needs adjustment (I have a TB reseal kit woiting for install)
Thanks everyone!
~Eyal

Luis de Prat

I know you're not exactly "rolling in the dough" right now, but you say you sealed the BOV up with JB weld?!

With the amount of pressure that thing takes, I would spend the $25 and at least get the 993TT part from the dealer.

Eyal 951

Idle stabalizer valve. I have an Evolution diverter valve, the $120 dollar one on paragon.
~Eyal

Luis de Prat

OK, now that sounds like overkill.

Eyal 951

How so? Billet, the thing wont fail, like the stock (or 993TT) do a lot, it flows more, so i dont ever have to mess with BOV again as I mod, and it's, um, pretty!
Any insight on the issue at hand?
~Eyal

Luis de Prat

Well, for that much money you practically have a brand new ISV, which sounds related to your problem. I've had a 993TT BOV on my 951 for years now, and it holds up just fine.

I just put a new ISV in my S2 and the idle response is just plain wonderful.

How about the TPS? I remember you wanting to sell an almost new one. Did you replace it?

J Chen

Eyal,
Did you change the seals at the TB ?
Laust posted a thread sometime back about this.
After reading that post I pressure tested my system
& discovered that the TB seals leak big time.

DDP

Why don't you try running your car without the ISV hooked up? Just plug the manifold and the hard pipe and see how it runs...

Sami951

I don't think a leaking ISV would matter that much, since the leak would still kind of be within the system... on boost, there's going to be pretty much equal pressure on both sides of it. On idle it's supposed to let some air through, to keep the idle stable (hence the name ).

hosrom_951

Eyal: I get 14Hg when cold and 17Hg when warm, no leaks even after using the pressure testing method and carb cleaner sprayed all over the intake (both when engine is cold and warm)

You're fluncuating idle is similar to what i encountered in the past; That is, high idle when warm. I replaced the TPS and the idle problem went away. But do check the TPS both at the switch itself and at the KLR for voltage.

You mentioned pressurizing the system at 12psi and it lost 1psi in ~20 seconds or so, i believe that is normal (but i could be wrong).

F18Rep

Eyal, I don't have a good reference for those leak down numbers, but I can say that even with 1 pound per second of loss, I have seen good performance - no stumbling and able to reach almost 18 to 20 lbs of boost with a semi stock system (ape chips). The TPS is pretty easy to test and there just happens to be new on ebay (no affiliation) as of yesterday. Just a thought. ...Bruce

Eyal 951

So its supposed to let air out of the housing? Did I just make myself sound extremly dumb? If so, thats worth laughing at, but if this is true I Definetly need another ISV now.
I'll check the TPS.
~Eyal

Mike S

Eyal, I had a similar problem where mine was hovering around 12-13 when cold. I changed the throttle body seals and it spiked to 16 when cold. Looking back now, it should have been obvious since I could hear escaping near the throttle body (out of the TPS body actually).

Sami951

Eyal, my bad - it's definately not supposed to let air out of the housing, I thought you meant it was leaking as in letting air pass through.

azmi951

I replaced my ISV and JB'ed the housing on my new one. After I put it in it ran very well. I can not confirm my old one was leaking but I would think it was.

This tip about sealing the ISV up came from a rennlister who has been there before.
Eyal, I got my new ISV off ebay new for $40 it was listed as a 911 part but it was the same PN as the one I removed.