I was driving my 99 Boxster with an 02 S engine replacement. The engine was cold and I was cycling through second gear at about 3K RPM when there was suddenly a rather loud hissing noise from the engine area. There was not an immediately noticeable change in performance. I proceeded to limp back home (about a mile away). I noticed the following things:

A very strong odor of rotten eggs, you know the cat converter kind

Significant loss in power and response, had to really feather the RPM and clutch to get it going.

When the engine was revved, the noise went away, but as soon as I let off the accelerator, it came back

The engine seemed to want to stall, but never did

A significant loss in braking power

Does anyone have any idea what I'm looking at here? The closest dealership is an hour away and a long tow truck ride. I would like to at least know what I'm getting into before I break the news to my wife that I'm going to cancel a future vacation for my "stupid car" (her words).

1. The hiss sounds like some sort of vacuum or exhaust leak. Which could cause all sorts of mixture problems.

2. The sulfur smell goes along with mixture issues

3. The loss of braking goes along with loss of vacuum. Power brakes operate on vacuum servos.

So --- i don't want to speculate much, but I'm thinking some hose went "pop" and resulted in all 3 problems. Overall, that's a good thing since nothing you mention sounds long-term damaging.

I would open up the clam-shell and look for stuff that's torn, popped off or otherwise disturbed.

Grant

In talking to someone else, their thoughts go immediately to a manifold vacuum leak. It is a vacuum at lower RPM rather than a ported vacuum at higher RPM. The brake booster apparently relies on this manifold vacuum to operate. How does that coincide with your thoughts? Thanks for your feedback!!

i dont knwo enough about boxsters to claim that a leak in place A has a difference effect than place B.

But overall, we agree - its a leak. For the record, most are connected, so a leak here and there have the same effect. It really does not matter where you get a nail in your tire - it all goes flat.

Grant

Edited 1 time(s). Last edit at 10/19/2011 10:34PM by Laz. (view changes)

It could be as simple as a loose spark plug.

What were the most recent things you had done to the car? A problem like this almost always happens because some prior mechanical work was not done properly.

Also, it's possible that the engine has stored a fault code, even if the check engine light is not on. If you have a code reader or a nearby auto parts store you can have the code read for free. Post the code here and we will give you a lot more info.