Why didn't I do this years ago!!

[full quack]

Hey folks,
I know others have done this, don't have a clue why I didn't do it years ago.

I finally had it with my hunting idle, and I removed the decel valve, and re-routed my dizzy vacuum advance hose directly to the throttle body, by passing the thermo switch.
Sheeezzzz...does this thing run & drive better or what!

I also replaced my rear wheel bearings, now that isn't a job for the impatient or timid. I know I'm slow and methodical, but damn that took a long time! It wasn't a difficult job, just time consuming as all get out.

Mark

[drmatera]

when i first got my car the CIS worked horribly. disconnecting the o2 sensor helped a bunch but ditching the decel valve and bypassing the bypass valve was the biggest improvement next to EFI'ing the car.

[mfiazzo]

do you guys have some instructions or some pics to show the rest of us how to do it?

[tj930]

+1

Is it the Mark-Houghton method? (Involves a hacksaw and 'skills'?)

[drmatera]

mfiazzo, I learned how from this site... do a search on decel valve

[aschen]

Originally Posted by full quack

Hey folks,
I know others have done this, don't have a clue why I didn't do it years ago.

I finally had it with my hunting idle, and I removed the decel valve, and re-routed my dizzy vacuum advance hose directly to the throttle body, by passing the thermo switch.
Sheeezzzz...does this thing run & drive better or what!

I also replaced my rear wheel bearings, now that isn't a job for the impatient or timid. I know I'm slow and methodical, but damn that took a long time! It wasn't a difficult job, just time consuming as all get out.

Mark

Did your decell poping go crazy with the valve revoved?

[gsxrken]

I'll take that decel valve if it's all same to you. Used they seem to go for around 40 or so- I've been looking- can you PM me?

And I hear you on the rear bearings- I had to do them shortly after I bought my car. I removed the rear banana arms and brought them to shop where I could press them out myself. I was sweating over those $1500 cast aluminum arms, let me tell you.

[drmatera]

no

[e170drvr]

Hmmm, I just put my decel valve back in.

[drmatera]

let me clarify the "no". No i didn't notice any more popping on decel.

I sold all my old stuff last year as I never plan to go back to CIS

[full quack]

This an easy-squeezy job. No cutting or anything. Just unbolt, and plug the needed openings with the bungs of your choosing! Re-set the idle, and your done.

I noticed only a slight increase in off throttle popping, it is of no concern to me.

I'm keeping all my stock stuff, as someday when I sell it, the new owner may want all the stock stuff, for better or for worse.

Mark

[mark houghton]

Originally Posted by full quack

This an easy-squeezy job. No cutting or anything. Just unbolt, and plug the needed openings with the bungs of your choosing! Re-set the idle, and your done.

I noticed only a slight increase in off throttle popping, it is of no concern to me.

I'm keeping all my stock stuff, as someday when I sell it, the new owner may want all the stock stuff, for better or for worse.

Mark

+1.

TJ930: The "Mark Houghton" method went way beyond just deleting the decel valve (in fact, I'm still using it to vent additional boost to atmosphere...to supplement the BOV). My goal was to create a system that deleted the decel valve, deleted the stock recirculation valve and manifold, and utilized an aftermarket BOV to recirculate the boost charge...while retaining the shortneck intercooler. Much easier to just buy a longneck IC, rubber elbow and BOV. But I sure enjoyed the "hack and tune"!

[drmatera]

wait till you finally climb out of the CIS stone age and go EFI. You'll be posting this same exact thread title.

[911st]

edited.

Originally Posted by full quack

...I removed the decel valve, and re-routed my dizzy vacuum advance hose directly to the throttle body, by passing the thermo switch...

Glad it is working for you.

However, here is my two cents:

On a 914 the deaccel valve is nothing but a smog device and an irritation.

On a 930 it helps with several things besides emissions.

It helps keep the rpm's (and boost) up a bit between shifts.

It also acts is a mini BOV in that it passes air around the throttle plate and thus less stress is on the turbo between shifts (especially if the BOV fails).

It also helps reduce over-swing of the metering plate with shifts. Even with the bypass this over-swing creates a brief lean condition when getting back in the gas.

There is a Porschee WUR damper that can help with this and on the later C2 Turbos they actually added a special bypass valve to the Fuel Distributor to lessen this issue. RUF used the dampener on the BTR and Porsche used it on the 930 SE.

These are probably not big deals as many seem to have been happy with removing the De-accel valve. It dose improve preserved throttle response as the motor will de-accel faster.

On the dist bypass. Do you have the two connection pot? Did you bypass the solenoid to?

[full quack]

Drmatera...I can't afford EFI!

911st...mine is a EURO '84, I have no solenoid in link with the dizzy/vacuum lines, either electrical or vacuum.

My dizzy has 2 vacuum lines, 1 for advance, 1 for boost retard. Thats it!

I have simply by-passed the timed/heat switch on the engine block. All vacuum lines start & terminate in the original locations, just no more detours.

The car now idles perfect, shifts way smoother, and I have crisper, quicker pick up out of corners. I'm guessing that my stock decel diaphram has been compromised for some time now, and I just didn't know any better.

Mark

[JFairman]

"and I have crisper, quicker pick up out of corners"

Then there is a possibility that (emission control) thermovalve in the vac advance line was worn out and never opening, and if thats the case you never had any vacuum advance until you recently bypassed it.

[911st]

Excellent.

I truly think there is a lot of opportunity to wake up the CIS 930 by working the ignition side.

I do not think you have Vac-Advance. Only Vac-Retard and Boost-Retard.

Typically the way the 930 two pot system works is timing starts at about 0 deg. Jumps to about 8-10 deg with first accel as the vac-retard falls off. Then mechanical advance at rpm takes timing up to around 25 (to 29 euro) deg's. Then on boost timing is pulled back to about 16-18 deg.

This seems for the most part seems very conservative settings probably to live with having little ability to adapt to different environmental conditions, CIS's poor low speed atomization, and or poor fuels.

I wish they had Vac-Advance. If we could get into the mid 30's on cruse it would probably help with throttle response, lower temps, and better MPG's.

There is probably also much crisper throttle response off idle and even more power on boost with more advance. (The 91-94's CIS turbo's run more advance but can pull timing with higher temps).

The best.

[full quack]

Yep all together possible, I'm guessing a little of both. Thermovalve & decel diaphragm issues.

You know ignorance is bliss....right up until somebody (or even yourself) enlightens you......then you just feel like a moron, sheezzz.

Anyway, car is happy, I'm happy, it's sunny in Seattle...all is good!

Mark

[gsxrken]

When a decel valve no longer holds vacuum, what is the impact? Certainly, it won't open when it should to do whatever it does when it's open, but does a leaking one constitute a vacuum leak, so that removing a bad one would be better than than leaving it connected?
Is that why Mark may have picked up some response?

[mark houghton]

Originally Posted by gsxrken

When a decel valve no longer holds vacuum, what is the impact? Certainly, it won't open when it should to do whatever it does when it's open, but does a leaking one constitute a vacuum leak, so that removing a bad one would be better than than leaving it connected?
Is that why Mark may have picked up some response?

Most likely. If the diaphram inside were to spring a leak, both scenarios as you've described might be likely. You would be sucking in un-metered air anytime vacuum was present, and leaking out pressurized air when on boost. Bad scenarios, both.

All these redundant and basically unnecessary things that can fail - including the temperature sensitive ignition advance valve, can cause real gremlins that are hard to trace down. My motto: Do away with them unless absolutely necessary. I'm about as stripped down of that useless junk as I can be and tuned almost as good as it gets with CIS. The next step would be to save serious pennies for EFI....but, now that I've got the CIS all figured out (well, almost, with the help of everyone here), I wonder just exactly what the payoff would be if I took the EFI leap?