Carrera "Idle Hunting" Problems

[PcarRacr]

Hi All,

I wanted to see if anyone else has experienced this. I did search the archives but wanted to add one more ptoblem.

First off, I have an 85 Carrera and once it is warm it hunts during idling. I have replace everything except the Idle Air Valve so I guess that is next. However here the BIG problem....The car will not pass Smog and it is Off the Charts when it comes to registering CO2. So basically it is WAY Rich and I mean it is off the charts. The car does have a "Chip" in it but it has been smogged multiple times with this "Chip" and never a problem before.

I just changed the Head sensor so maybe that will help with the richness(I haven't tried to smog it because it still hunts) but I wanted to ask the group is the Hunting Idle is still a sign of being "rich" at idle. Oh yeah it doesn't always "hunt" when it is warm.

Also any other Ideas on why it is so Rich is greatly appreciated!!!

As you can imagine I have been chasing this problem for months and it has cost me lots of $$$ and yet still no luck.


Thank In advance,
Chad Armstrong

[armandodiaz]

I'm interested in this subject. I also have an 85 and it hunts but only in heavy traffic when the car is at it's hottest. I've been doing pretty good at avoiding heavy traffic but if there is a problem when the car is hot then I imagine there has to be a problem all the time. It's just something that has been lingering in the back of my mind. One thing I have noticed if I'm in heavy traffic and it starts hunting as I'm creeping up with just a few high revs it goes away. I've learned to just easy off the clutch to creep instead of hitting any gas. So far I've only replaced the head temp sensor and DME relay. These are 2 things that always go bad so I figured, why not. I also noticed the breather hoses to be cracked. I bought the replacement hose but have been too lazy to change it. My theory is when the car gets super hot the cracks expand and causes vacumn leaks. Sounds good, in theory, but haven't provened it yet.

[Jeff Alton]

Have you had the mixture adjustment checked? It can be done fairly accuratley with a digital volt meter, but should be done with an exhaust gas analyzer. Also, I agree, vacuum leaks could also be your problem, but they will usually lean out an engine not make it run rich. Unmetered excess air enters when you have a vacuum leak. I just checked and tightened everything on my intake manifold including where the manifold seals to the head and I now have a rock steady idle.

Hope this helps

Jeff

[PcarRacr]

My Mechanic did ajust the mixture to try and lean it out. That's about as much as I know.

My plans are to plug a stock chip in it and replace the Idle control Valve(Motor) and hopefully that will cure it.

I just noticed that the last time this was brought up was in 2001 so I wanted to ask the group if anything has changed in the last two years.

Thanks Again
Chad

[ruf-porsche]

See my reply to stumbling and possible source of a vacuum leak.

Stumbling at low rpms-'88 3.2 Carrera

[nut11]

I had the same problem with my 85 carrera coupe. Searching in the rennlist forum, I found that if you gently but firmly tap the idle stabilizer valve with a hammer and then spray wd40 inside it, disconnecting the hose, the problem cleared up. The tap apparently dislodges the valve component and the wd40 cleans things up inside. Do that b/f you buy a new one. Good luck.

[Por_sha911]

I sprayed carb cleaner in the ISV. I can hear it move but not freely. Is it suppose to "rattle" inside when you shake it or have a kind of slow thud?

[kepperly]

I second nut 11's diagnose but hit it with a hammer?. Just take it off, clean it with carb cleaner, blow it out, reinstall. HAMMER !!!
Then get an old black relay remove the top, clean the contacts and make sure it works, then plug it into the blank hole by your coil.
Adjust the idle to 850-870 then depress the contacts and readjust until there is no differance. You are done!!

Keith Epperly- 87 carrera cabriolet tubo look slant nose

[nut11]

Kepperly, using a hammer can be construed as a bit more than is necessary but the intent is to dislodge a stuck valve not beat it to death. Instead, use the handle of a screwdriver. The ISV is a tough cookie. Porccha911, I don't think it should rattle inside. Did you have any success?

[stlrj]

But if you unplugged the IAC (idle air control valve) and it still hunted...it's not your IAC.

The IAC will not have any effect on mixture either.

[DonMo]

My 84 hunted too but when cold. My P-car was chipped too (Vertex replacement DME with chip). I figured out their was a series of variables you had to deal with.

I got sucess by first putting in the jumper and adjusting the idle to just below 800 rpm when fully warmed up. I also adjusted the air mixture to where the 02 sensor was cycling between .2 and .8 consistently. Now no hunt. My guess is that the chip had idle mixure rich and the DME was fighting to find the right level.I know fuel mixture is the variable that makes the difference because I could change the DME settings to go rich by 3% after I made the hunt disappear and it hunted again.

I also learned that with a warm car, you can take the Idle control valve and disconnect it and you will hunt. You can also disconnect your 02 sensor and you will go real rich. Hope this helps. I don't know why lowering the rpm worked, everything says the idle should be around 880 rpm.

[stlrj]

everything says the idle should be around 880 rpm.

880rpm is if you have the later 87 control unit, otherwise 800rpm for 84 to 86 per spec book.

[stlrj]

You can also disconnect your 02 sensor and you will go real rich

Don,

How can it go rich if it is adjusted correctly to spec: CO... 0.6-1.0*
*Measured ahead of cat. conv. and with oxygen sensor plug disconnected. Technical Specifications 911 Carrera, 911 Turbo 84-87 Models

Cheers,

Joe

[dickster]

what DonMo said.

is your 02 sensor hooked up and working? when it fails it goes into "rich" mode doesnt it?

[rburn]

got sucess by first putting in the jumper and adjusting the idle to just below 800 rpm when fully


I didn't think one could "adjust" the idle? I thought the DME controls this via it's sensors, flywheel speed sensor etc?? My 84 seems to idle low like at 600, but the smog check i just had a few months ago showed it at

rpm %CO2 %O2 HC(PPM) CO%

802 14.6 0.2 32 0.16

2322 14.5 0.2 21 0.48

passing fine, but it seems to idle a bit low. I guess i need to get a rpm sensor gauge to see what's really going on... maybe the tach is that much off?


Thanks

[slakjaw]

if you UN-hook the IAC with the car running or even with the key on, the computer looses track of how many steps it is in or out. Which causes the motor to hunt for idle.

Try this

First cleen the IAC

Then clear the computer memory

Then start the car let it idle for 15 minutes with all accorys turned off, do not touch the throttle in this time. After the 15 minutes shut it off. Restart and let idle for 15 more minutes.

That should fix it unless you have other problems like vac leaks or other things wrong.

Kyle

[Lorenfb]

High CO2 numbers should not be a problem, as the higher the better,
i.e. CO2 is an indicator of complete combustion. CO is usually the problem.

First, remove the chip and install the stock one, which should always be done
when emissions problems occur. Then check following;

1. temp sensor
2. fuel pressure
3. idle switch
4. disconnect idle valve & adjust idle screw to bypass valve & electronics,
i.e. will help isolate the problem between mechanical (e.g. air leaks)
and valve/DME control
5. disconnect the O2 sensor

Check out his web site, www.systemsc.com on the Diagnostics page
and the Problems page.

[PcarRacr]

I just wanted to say thanks to everyone that respoinded. Yesterday I took out the IAC and cleaned it...I put it back in the car and it hunted for the idle even when the car was cold...however I tapped the IAC with a screwdriver and instantly the hunting stopped...it would idle for a few minutes then hunt again...to which I would tap and again the hunting instantly stops. I did this about 6 more times. So my guess is the IAC coupld probably be replaced and the hunting should stop.

I have replaced everything else and the mechanic says the cat is working properly so this time it shoudl pass Smog. I will keep the group posted and thanks again for the help!

Chad

[armandodiaz]

I cleaned out the IAC and the idle seemed to be smoother. Now I was only having problems when the car was at its hottest, in rush hour traffic. I problably will replace it because of it's age and its not a real high $ item. I did notice when I moved the IAC it seemed like there was something loose. Is this normal?

[Por_sha911]

Unhooking the IAC messes up the computer.

Quick Question: How do you clear the computer memory?