SEATRA

Yesterday I took the air cleaner assembly off to look over the water valve (HVAC system provided no heat inside car). The valve cycled fine with vacuum so I'm beginning to think I have a motor/mixing flap problem. I also noticed that some time ago a critter had made a nice nest in the V section of the motor right under the air cleaner.

While cleaning out the nest I ran into the unconnected vacuum line for the right fuel pressure regulator. Well after connecting the vacuum line and putting the air filtration back in place I fired her up to warm up the water and manually manipulate the mixing flaps in hopes of getting some heat flow into the car. Once warm I did indeed get the heat I was looking for so I'll be shifting my troubleshooting efforts over to the flaps/ motor control.

After all that I needed to go for a little drive. While driving I noticed the engine seemed to have quicker throttle response. I pulled over, engaged the clutch, and blipped the throttle to about 3500 RPMs few times. RPM went up just fine but when falling off it drastically slowed it's deceleration rate at about 1800 RPM all the way to idle. This happens under load too and is most evident when manually shifting at lower speeds. The engine will go all the way down to idle but just takes a significantly longer time to traverse the 1800 to 700 RPM range. I figure the newly connected right fuel pressure regulator has something to do with this. Don't know how long that thing was not connected. I put a shot of techron in the gas tank. Any other ideas ?

hacker-pschorr

So it takes longer to drop down to idle speed than before?

I'm guessing the vacuum line is also connected to the vacuum limiter (big disc thing on the side of the throttle body). This device slows down the rpm drop when the throttle is closed.

I took mine off.

fbarnhill

Hi,
Isn't that thing called the decelleration valve? My mechanic at Eurowerks in Charlotte hates the darn thing. He disconnected mine and plugged it. I had to admit, I liked the way the engine ran without it. It's been around 4-5k miles now with no issues.

Good luck,

hacker-pschorr

Deacceleration valve / vacuum limiter = came things. On other car (non-Porsche) it's called a vacuum limiter since that is what it's actually doing, limiting the amount of vacuum generated in the intake. 100% for emmisions.

SEATRA

Thanks Hacker! Are we are talking about part no. 928.110.173.01 vacuum limiter (according to PET). If so then I'll check it out and disconnect and plug the vac hose to the bugger. Did you take the entire limiter off the TB?

hacker-pschorr

My PET shows 930 110 190 00 --or-- 930 110 173 00, looks like we are talking about the same part.

I removed it completly.
Something I learned from Porken, when you remove the limiter, disconnect the closed throttle switch. Otherwise when you close the throttle in neutral or with the clutch in, the engine will almost die. The closed throttle switch work with the vacuum limiter - cuts fuel totally to the motor while the engine is coming down. Without the vacuum limiter attached, you are starving the engine to the point it almost stalls.

PorKen

5/8" and 3/4" rubber heater hose blockoff caps from any parts store.



The factory deleted the limiter on '83-'84 L-Jet cars with automatics. LH cars don't have them. (Except Switzerland, Australia, and Sweden; PET shows a spaghetti of hoses to fit the limiter to LH.)

999 703 171 40 - 14x15 cap
999 703 172 40 - 18x15 cap

SEATRA

Cool, I'll give it a try. Any downside to this?

SEATRA

Is the closed throttle switch to lower micro switch on the opposite side of the TB? Just disconnect the wires?

hacker-pschorr

Yes, the one on the bottom. I just pulled off one wire - keep them from flopping around too much.

SEATRA

Hacker you were right on with the cause of this one. Just completed the limiter removal and she winds down just fine. Thanks to PorKen for the cap info. Having the right size cap before removal helped me complete the job a lot faster. THANKS!