vanster

Why is it that on the PET diagram shows vacumm lines and the one on my 81 is plugged? 5sp vs Roger box?

Speedtoys

Someone skipped a step in the past..

vanster

What would be the reason?

G8RB8

Why would anyone want to wet their MAF?

Speedtoys

Not familiar with the use case for that part..

granprixweiss928

Thats the decel valve.

allows air to bypass the throttle plate on decel, so the engine doesnt stall.

you dont have a MAF in that car

Majestic Moose

That is the vacuum limiter introduced in 1983 so perhaps your throttle body was switched out for a later unit and this was capped off?

The Forgotten On

Funny that Porsche says the autos don't need it. When mine went bad my 81's engine rpms would rise and fall while coasting in a cyclical fashion. It was odd.

I would have it hooked up personally but many run without it with no problem.

granprixweiss928

it was not introduced in 83. My 81 has it. I think its on any K jet or L-jet engine.

Majestic Moose

You are correct, looking further it goes all the way back to '78

hacker-pschorr

Removing this device allows the engine speed to plummet very rapidly when not under load. This is bad for emissions and can also cause the engine to stall out. I suspect if you free rev your engine and take your foot off the gas, the RPM's fall to below idle and "bounce" back up. That's typical when these are bypassed.
The idle switch is often disconnected with this "mod" too, which allows raw fuel to be dumped into the exhaust giving you that "snap-crackle-pop" sound on deceleration.

I ran my 81 like this for a while and put it back on. Frankly it's annoying since randomly the engine can stall if they fall too fast and the computer doesn't catch it. It also made the car more difficult for my wife to drive since the engine speed would fall so fast between shifts it made for abrupt driving.

Modern cars control this via the ECU.

vanster

The consensous is to plumb it as per the PET . Toss the nipple. This could be one of the reasons I had such a difficult time trying to keep the car running.