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Question Decel Valve - Possible Re-install...

This is a picture of a stock Decel Valve on the Special Wishes 330BHP engine. Does anyone know where the hose with the Yellow Arrow is going?

I like my RPM's dropping quickly, however, I'm having a bit of an issue with the engine almost stalling when I have to take my foot off the gas and push in the clutch... I'm thinking about re-installing mine, and might just put it on the right now that I have a lot of room over there...

Also, I think I could address the "potency" of it by partially restricting the amount of air going through the main hoses.

Thanks!

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LIVN80S - - Red '79 Porsche 930 Steel Slant Nose Conversion [in 1987] w. 46k miles 3.3L; 964 Cams; K27HF @ 1.0 BAR, with Garrettson Intercooler; Rarly Zork; CIS Flowtech Fuel Head & BL-WUR.
Old 11-04-2014, 12:37 PM
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That should be running to the slidevalve. Search under my name and you will find pics of when I removed mine.
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Old 11-04-2014, 03:42 PM
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I put my decl valve back on too. Much happier now. Stays on boost easier when up shifting too...

Bo
Old 11-04-2014, 03:49 PM
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mooney, the hose you highlighted with the yellow arrow goes to a spout on the primary intake manifold (it's the top portion of the double spout that I think 16V is referring to - the bottom portion of the double spout is connected to the secondary intake manifold - aka: recirculation/blowoff valve) . . . that way, air is routed "after" the throttle plate when the throttle is closed and the decel valve opens via vacuum.

PS - I don't use the deceleration valve (Porsche calls it "vacuum limiter") and I don't have stalling problems. I bet you either have a minor air leak that is causing a momentary too-rich idle condition or your idle afr is too lean and that is causing the stalling (sort of a wild ass guess since I don't know the specifics of your system). Oh, and Brandon must be stoned regarding his AAR comment - ha ha ha!

Last edited by Ronnie's.930; 11-04-2014 at 04:22 PM..
Old 11-04-2014, 03:58 PM
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No ridiculous decel valve here either and it runs perfect all the time.
Recurving your distributor for way more low speed timing without going too far up top helps the pathetic smogged out way these cars run when stock more than anything but if you don't know what you're doing leave it stock.
Old 11-04-2014, 08:30 PM
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I'm going to initially take Ronnie and Jim's advice and look at other areas (air leak and/or timing) to see if I can get the "almost stalling out on DeCell" fixed.

Maybe post a video for added info. Thanks guys!

Will report back.
Old 11-05-2014, 02:03 AM
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Quote:
Originally Posted by mooney265 View Post
I'm going to initially take Ronnie and Jim's advice and look at other areas (air leak and/or timing) to see if I can get the "almost stalling out on DeCell" fixed.

Maybe post a video for added info. Thanks guys!

Will report back.
i took it off. made shifts worse. RPM's were hanging too hi too long, and i DONT speed shift my car. its also ugly.
i liked the thought of boost staying in when letting off the gas but i am not sure if that would help since my DV is controlled by manifold vacuum, plus the sound is pretty cool when it opens.

now my car is stalling when i let off the gas but only after fixing my air leaks. but now i am running very rich, like 12-13's at cruise.
i am thinking(hoping) its just a matter of timing/system pressure/control pressure and mxture setting.
i have leaned the idle mixture a little and it has helped.

i have the euro setup on my car.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 11-05-2014, 06:31 AM
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I took mine off years ago, only needed a slight idle speed adjustment after removing it. Car runs sooooo much better, shifts better, sounds better, looks better.

Albeit mine had a pin hole leak in it so that is why I first removed it, but if I ever get another 930, I'll rip that sucker out first thing, working or not.

Mark
Old 11-05-2014, 08:13 AM
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As has been stated earlier: my car always had a bit of a stumble after pushing in the clutch with high [>2500] rpm's.

However, this past weekend, with he onset of very high pressure and cold temps, I adjusted my idle mixture a bit more rich. The car ran much better, however, I noticed that once the weather warmed back up, the stumbling effect increased.

I guess I can "lean it back up." But, wanted to get more at the root of the problem - since it's staring me in the face.

Some history: Like Jim mentioned, I had my throttle body butterfly's hole welded up some years back because I couldn't get my rpm's below 1k with the idle screw all the way in. Once I welded it up, I was able to see 900 when fully warm.

Obviously, this is still too high and points to some other area of concern:
1. Air leak before the TB? I've searched Hi and Lo - - not too sure where it could be?
2. Timing off at idle - - I did have the vacuum pot changed out some years back and am not too sure it's doing what it's supposed to at idle?
3. Idle too rich? I can say my car is much happier now at 12.5-idle than at 13.5. Of course, happier means higher idle, too! I've got the screw all the way in and it's 950 when warmed up...
4. I'm asking this to be sure: could an air leak after the TB cause this problem? My guess is that kind of a leak would only affect 1 cylinder and not all 6...

So, I guess I'm to believe that when others have removed their decel valve, they didn't have to fight the stumbling on decel with clutch in?

I'll try to post a video of the stumbling by tomorrow... Thanks!
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LIVN80S - - Red '79 Porsche 930 Steel Slant Nose Conversion [in 1987] w. 46k miles 3.3L; 964 Cams; K27HF @ 1.0 BAR, with Garrettson Intercooler; Rarly Zork; CIS Flowtech Fuel Head & BL-WUR.
Old 11-05-2014, 08:17 AM
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I have no stumbling with mine removed. No other modifications to the TB.
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Old 11-05-2014, 08:47 AM
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the AAV and the AAR do not effect performance unless they are bad. IE leaking unmetered air.

you have an air leak if you cant lower your RPM. the air leak can be before the TB, but it is after the AFM. are you sure the TB is in good working order?
i have been fighting air leaks for a year and just found my big one.
i had a bad hose connecting the IC up pipe from the turbo, my WG was leaking. my intake manifold was leaking. (i may have created that). my DV was leaking vacuum. every now and then i break an Oring on the throttle body putting the IC back on and dont know it til i take it back off. also check the long studs that screw into the manifold.
one other thing. check the vacuum line from the manifold to the brake booster. you should be able to pull a vacuum on it and it hold.

with a leak my cruise AFR was in the 15's, sometimes 16's. i could set the idle to very rich and it liked it. i also had my idle set to 850 rpm and it liked it.

with leak fixed my idle dropped even more, to around 600. but then my cruise AFR is in the 11's and 12's but the car LOVES it. GREAT throttle response at low RPM and off boost. but my idle mixture was now in the 17's.
long story short (too late), i have/had the same issue when letting off the gas after trying to get good idle AFR's and cruise AFR. RPM's drop to 0 and bounce back up. leaned out the idle some and it is better so far. when the idle would drop to 0 the AFR was around 10, then both would come back up with AFR settling at 13. now it is 14.
i have also done some things i dont suggest. i lowered the fuel volume out of the fuel distributor. DO NOT do this. if you suspect the FD is bad, send it off.
cruise AFR is 13.4 to 14. it really does not like it this lean.
i am not sure about my system pressure. i ahve 2 gauges that read 2 different values. if the one gauge that reads low is correct, that would cause me to be rich.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 11-05-2014, 10:03 AM
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Your picture is not from a stock car, see what a stock 78 930 (except the air filter) looks like and BTW it runs great!

Old 11-05-2014, 11:52 AM
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