I just went through this myself. My idle was surging badly about 600-800 rpm.

I suggest first buying the Bentley Manual, and doing the sequence of resistance checks to eliminate the sensors and throttle switches as problems.
You can check your throttle bypass valve manually by taking it out once the engine is warm, and looking down the throat to make sure it is holding steady at halfway open.

If all of the electronic sensors and afm checks out, then you have to start looking for vacuum leaks. You can sort of confirm this by listening to the bypass valve working while the car is idling. Anyway, there are a LOT of places where a vacuum leak can occur. I found it very useful to have several good work lights and a good sized inspection mirror. You will need to take hoses off everywhere and inspect the ends, and replace hose clamps. The hose clamps on the ICV can be tightened up a bit with a pair of sidecutters.

Stick with it, and you will be rewarded by a sweet running, very reliable and more powerful motor.

I've cleaned the ICV, the idle micro switch operates properly and still the idle bobs. Now as for the ICV resistance values; they are 16 Ohms and 20 Ohms (from center pin to outer pins). I'm off by 4 Ohms on one side. That's out of tolerance by 20%:eek: Would you consider this the definitive source of my problem?

I've got a spare ICV you can try. Send me an IM and we'll work things out.

T...

Trog, you have mail.

Bingo, we got a winner :eek: after 20+ years, it's time to replace it

I think you can get that much error from one multimeter to another, or dirty contacts, etc.

I think your problem is somewhere else. Keep going, and check the cyl head temp sensor, the air flow meter box, the full throttle and closed throttel switches, and the adjustment of the throttle microswitch.

I'd also do a visual and handcheck of your vacuum hoses. Look for cracks, or signs of oil blowing out through a crack.

+1 on that, check to make cerain the meter is known to be good.

Check the OHM's on all components and elliminate before you replace.

Get some ETHER (started fluid) to check for Vacuum Leaks,

Best wishes Brother,

+ 1 for Steve W recommendations. I did the same things in that specific order. Verify hoses for air leaks, cleaned and lube the ICV, re-adjusted the AFM to 6.5 turns and re-adjusted the idle control. Car now idles at 850 steady. Still have to fine tune it for accuracy but I am more than happy with it now. Own the car for over a year, no P car expert. Did a lot of research here.

I agree, one meter to another: but you won't get that much error from the same meter. One side read 16 Ohms while the other side read 20 Ohms consistently as I checked and re-checked. It's now a known out-of-tolerance part in my eyes. I'll swap with a known good unit and see...I don't want to start chasing something else while I have "one in the hand". ;)

ok,
cleaned the ICV with carb cleaner and then shot it with silicon lube.
that is a definite to do for any body suffering any kind of hesitation for sure.
I think that actually cleaning the ICV should be the first thing
so I've also replaced the dme relay
the cht sensor
plugs and wires
distributor cap and rotor
back in april the alternator was replaced.
tried to rebuild it but it was shot and the guy who did it didn't charge me for the rebuild after it didn't work. good guy. put in the new alternator and it works fine
I still have the O2 sensor plugged in and put a SW chip in a few weeks ago
just took her out for a spin to warm up and see how the idle is
runs really great
better than it ever has
of course this is the only 911 I have ever driven so it is tough to know if it is really spot on
with the O2 sensor plugged in it feels real "cammy" feels like it picks up in steps
and with it unplugged it feels linear but not as fast revving
don't know if any body else gets that reaction from the motor
and the stumble I had at 2500 rpm is gone
hopefully for good

Sounds like the idle mixture needs to be adjusted, along with the base idle speed. See the following threads for more info:

http://forums.pelicanparts.com/porsche-911-technical-forum/376357-rpms-hanging-s-wong-chip-rough-idle-again.html

http://forums.pelicanparts.com/porsche-911-technical-forum/104495-idle-hunting-problem-continues.html

Hi Guys,
I have an 87 with 42k. Runs great. On cold start it idles at 1200rpm for a few minuets then goes to around 850 or 900 rpm. It then hunts very slightly. Maybe 50 rpm up and down at most. This certainly isn't a huge problem but is it the start of a bigger problem? Do you think I could benefit from an ICV cleaning? Do these cars ever idle at around 850 or 900 without any hunting whatsoever?
Thanks,
Jeff

01sport,

I'm certainly a novice at 911 issues.......but I cleaned my ICV last weekend due to a stalling problem and now she idles at a rock solid 850 rpms.

01Sport,

If the ICV has never been changed, it will be going on 26 years, bound to build up gummy oil in it and the electronics in it could be failing.

Your Baby must warm idle at 880 RPMs (+/- 20 RPMs), it must not HUNT! HUNTING IS NOT NORMAL

Try the cleaning, slight lube and test the OHMs just to be certain, replace if necessary. It is quite easy and Pelican Parts sells them.

I'm no fuel injection expert, but I stayed at a Holiday Inn Express last night......an '87 with 42k miles?

I think your main problem is that you don't drive the car enough, and expect it to run perfectly after sitting for years with no use. Seriously, these cars need to be driven. Putting them back into use requires checking hoses, brake componets, flushing fluid, checking or changing belts, oil leaks, and the list goes on and on.

I'd say your 911 is running admirably well under the circumstances.

300 thanks for the reply. Exactly what I was hoping to hear.

Your Welcome SoCali ;)

when I want to adjust the idle
how do I jump the plugs?
I am sure that sounds like a stupid question

I believe you can disconnect the ICV, set to your year's specs the re-plug it in. Other's more tech should hopefuly post.

My Mechanic hooked up a device in the round terminal on the driver side wall of the engine compartment to check my idle. He said it disabled the ICV. I figure disconnecting the ICV would be the same thing, no?

I have no idea
but I have to conect those two plugs some how to adjust the idle