3.4 DOHC vacuum leak

[Series8217]

So it turns out I've got a vacuum leak.
With the IAC closed completely I'm getting an 900 - 1000 RPM idle. It has idled properly since the rebuild, so something has changed since, even though I haven't removed the intake or anything..

The motor is a 1993 3.4 DOHC.

All gaskets are new (motor was rebuilt last summer). What are the common or tricky places to have vacuum leaks on this motor? I have already tried capping all of the PVC system ports as I have a somewhat complicated setup.

[Shaun41178(2)]

I usually spray carb cleaner at things till it sputters and thats where the leak is.

I dont know the usual locations where they can leak. I say give everythign a once over with the ole eyeball and see if anythign is obvious.

[Aaron]

Steven, the first place I'd check is the brake booster and the Map sensor.

The map sensor and its vacuum acummilator are not very well designed, and the accum thingy doesn't seal well all the time. Furthermore they are VERY prone to cracking do to the multiple wires/hoses running to it, and on it.

The brake booster should be fine, but I've had one leak before..

[Shaun41178(2)]

try not to turn this one into a flame war guys. keep it in your own threads not someone elses.

I will bring the mod hammer down if I have to.

[Fast88Fiero]

So it turns out I've got a vacuum leak.
With the IAC closed completely I'm getting an 900 - 1000 RPM idle. It has idled properly since the rebuild, so something has changed since, even though I haven't removed the intake or anything..

The motor is a 1993 3.4 DOHC.

All gaskets are new (motor was rebuilt last summer). What are the common or tricky places to have vacuum leaks on this motor? I have already tried capping all of the PVC system ports as I have a somewhat complicated setup.

I've seen the lower intake manifold gaskets leak on the DOHC quite a few times. I know yours are new but it could still be there.

[Aaron]

I've seen the lower intake manifold gaskets leak on the DOHC quite a few times. I know yours are new but it could still be there.

That is one thing I think the DOHC does well, is the intake manifold gaskets. I've never had, or seen one, that leaked. Even when old (100k+), they seem to do well. IMHO, it isn't any sort of gasket.

[Fast88Fiero]

I've seen the lower intake manifold gaskets leak on the DOHC quite a few times. I know yours are new but it could still be there.

That is one thing I think the DOHC does well, is the intake manifold gaskets. I've never had, or seen one, that leaked. Even when old (100k+), they seem to do well. IMHO, it isn't any sort of gasket.

Replaced a set last week on a 80K mile DOHC at work. I've seen a couple others with leaky gaskets. They are rubber 0-ring style and shrink/get brittle over time causing them to leak. It's no different than a Ford 3.8, 4.0, 4.2 V6 with o-ring style gaskets which leak all the time.

[Series8217]

Well, I did find some cracked hoses and a crumbling vacuum cap. Replaced all that and the thing idles and runs a whole lot better. Redid my exhaust too so it doesn't rattle the heck out of my car.
However, the BLMs are still maxed out even at idle. Apparently after all this hoo-hah my injector driver is pretty much dead. The ECM doesn't seem to be able to drive the injectors at low pulse width, it drops pretty much every pulse. At higher pulsewidth it works better but still not good enough to run at the right A/F. Who knows what else is going on in the ECM contributing to my driveability problems and etc.. so I'm going to replace it tomorrow or the next day and knock that factor out.