Intake Leak (can't find it, can't compensate with fuel) Options

[[Freemantle]]

I recently lost the rear main seal on my ST on the freeway, 700 miles from home. I siezed up #3 and beat the hell out of the sleeve.

So I replaced the engine. The mechanic royally screwed up my ECU harness and disconnected MAP signal on accident (I have a V-AFC wired, yes, I am using a V-AFC on purpose). I took the car home in limp mode to re-pin the harness myself.

Did it and the car ran great, stronger than when I bought it and smooth as all let out. I drove the car to work the next day without incedent. I came home for lunch and noticed that I was Idling very high (about 1200 RPMs) and the engine was making some unplesant noise, namely some raspyness in the intake note.

I tapped the trottle to make sure it wasn't stuck. No dice. The VAFC read an idle vacuum of -7.6psi. Prior to the engine swap, I was used to seeing -9.1psi (so the engine was under higher load now at idle than it ever was prior.

And the Idle climbed to 1250

and then 1300

and then I shut off the car.

When I fired the car back up 20 minutes later to go back to work, it was still idling that high and quite noisy in the front.

When I got off of work I bought a can of carb cleaner and some high-quality 22GA butt splices and male/female connectors. I redid my entire harness, and the Idle RPM still stays steady at 1300 RPM. Driveability is still supurb. I added fuel with the V-AFC. I added more fuel with the VAFC. I could get the RPMs to momentarily dip and manifold pressure to drop to -8.6PSI for a little bit, but it would regulate to the same idle speed and pressure a moment later.

I bathed the engine bay in carb cleaner. No dice. Can't find a leak althought I can **hear** the leak when driving (sounds like a supercharger spooling, if you've ever had an intake manifold leak you know what it sounds like).

Causes for concern:

A) Fuel economy is **** when at idle now.

B) The VAFC MAP sensor isn't to scale because I don't know the correct sensor type. I use 6in 6out because it gets throttle and everything else right. I was accustomed to the old motor Idling at about -9.1 PSI and pegging up exactly to 7.6psi when at WOT (I know it's wrong, just keep following me). Now I Idle at about -7.6psi and I WOT at 3.2psi. That means that I am getting worse performance @ wot than previously. I can't say that I feel difference, the ST isn't exactly a stunner, but just knowing that sucks.

So the Queston:
It has the symptoms of a leak, it sounds like a leak, it looks like a leak, but why can't I find it? And why am I pulling less vac at WOT?

Any help is mucho appreciated.

[[Freemantle]]

' date='Dec 18, 2005 - 10:27 PM' post='368745']
I bathed the engine bay in carb cleaner. No dice. Can't find a leak althought I can **hear** the leak when driving (sounds like a supercharger spooling, if you've ever had an intake manifold leak you know what it sounds like).

The only place where I may have not gotten carb cleaner was underneath the intake manifold. As soon as it stops raining, I'll pull the car into the garage and check the idle adjustment screw and put my interior back together.

[[Freemantle]]

Idle Air control was fine. Took it to the mechanic today. The noise I've been hearing that sounds like a whine is my water pump (which is going bad). He's replacing it, but he can't do it until next week Wednesday . The high rev is due to the bearings failing and the lack of proper load on the crank pulley. Thanks for all the suggestions.