mjensen

I have a few gremlins on my 86 951. A few minutes after a cold start the car will lump/hunt at a slightly lower idle speed. I did the idle speed adjustment via clarks-garage, a while a jump/bypass the idle valve under the test ports the idle is correct, unhook the wire and it lumps around again. My questions is , can you bypass this valve, or must it be replaced?

hosrom_951

You can bypass the valve, but the car would idle very low when cold and when the ac is on.

Better to replace it, Ian at 944online sell rebult units for ~US$80 or so.

Click Here

Porsche-O-Phile

Screw rebuilt since there's no way of testing it off the car - get a new one; only about $120 or so from Paragon.

hosrom_951

Jeff: Paragon goes for $145!

Porsche-O-Phile

Oop, yea just checked. . . I'd still get a new one though. . . Seems like an awful lot of people have been having problems with these lately so perhaps they're reaching the end of their useful lives. I actually have a used one to swap into my 951 but I'm not holding my breath that it will work (already tried one - worked fine for a month then same problem). If it doesn't work or ends up dying as well, I'm goin' with a new one.

Melchior

A lot of times these valves tend to get stuck mechanically, while still being electrically sound. Try using a lubricant on the valve like PB Blaster, WD-40, etc. Make sure that it won't freeze since it is getting colder out.

jerome951

True, and they can get stuck in the open position. Even with mine bypassed electrically, my idle was lumpy and low. I capped off the ports on the intake where the ISV attaches and my idle is now smooth again.

mjensen

Could you guys explain how you are bypassing the ISV?

Epic2112

I say just ditch it. Mine was bad an I capped off the ports for a year before I got around to buying a new one. A week after installing the new one I took it off again, I just like how the car feels much better without it. For what it's worth, I drove the car almost daily though a winter in Pittsburgh without any problems, just take it easy while the car is cold, which you should be doing anyway.

mjensen

Just verifying, are you removing the hose from the stabilzer to the intake and the hose from stabilizer to the interecooler tube? Do you have to jump or modify the ISV wire plug/harness? Anything I am forgetting?

Eyal 951

I bypassed mine, and can barely notice its gone. Not replacing it. Pull the hose of the intercooler pipe, cap that, pull the other hose off the intake manifold, cap that, unplug the plug and let it sit there, so need to jump it as far as i know.
~Eyal

jerome951

Look in Clark's Garage idle adjustment procedure on how to electrically bypass the stabilizer valve.

mahoney944

digging up an old thread here. I was messing with my ISV and tried the electronic bypass method. I was wondering when the electronic bypass jumper is in place for setting the idle, it puts the valve in its center position, but does the center position still let air pass through? I find that if I clamp off the hose completely so air can pass through at all I get a different idle then if I just do the electronic bypass to set the idle. ................I was thinking that if the center position of the isv closes the valve off that clamping off the hose to the idle stabilizer would be ideal for setting the idle since no air would be allowed through, which works fine. but then when I unclamp the hose my idle is too high. Making me think the ISV is letting too much air through or the isv lets a percentage of air through all the time even at its center position. does anyone know?

Rogue_Ant

The ISV at center position is, essentially, half-open.

However, when using the electronic bypass, the ISV isn't set to 50%, it is set to (roughly) 9% open.

Clamping the ISV hose, and then setting the idle is not going to yield good results... The system expects that there is a specific amount of bypass air (thus the 9% open), and uses that for all its ISV control.

mahoney944

Interesting. I am still looking to solve my idle issues with my m-tune. Soon I'll have the logger running so possibly that will help identify the issue or at least help capture it for review by this weekend. The idle issues I see are (1.) cold start, I get a super slow drop (nearly stops falling) in rpm from 3000 to idle. Once it warms up this goes away. (2.) Once warm I get a jerky idle drop where the rpms will bounce their way down coming to idle. (3.) Pretty rich at idle. If the car idles for a minute or two it creeps to maybe 14.2 eventually. It's just very delayed like it has to really adjust to get there....and see mid 10s at WOT. I've tried pulling fuel with the fqs with no luck.

Again logger install coming soon.