oscillating idle
 

If I have my o2 sensor connected the idle will oscillate by rougly 100 rpm constantly. If I disconnect the o2 sensor the idle appears to be steady, however, seems to idle somewhat rougher. Based on the tach I would place its idle in the neighborhood of 850-900. Not sure if this is relevant to this but when the car is idleing if I gun the engine to 2500 or so and let off the engine falls to 500 or so but quickly recovers, perhaps this is normal. Any suggestions or further troubleshooting suggestions I can do to narrow the problem down?

Also does anyone know what the plug in the below picture is for? I cannot see anything that it would plug into and can only assume that it may be some type of diagnostic plug.

http://forums.pelicanparts.com/uploa...1183062059.jpg

I also was going to check my idle adjustment but in going to jumper the B&C ports I found that on my 89 they are not there. I have a hole in the metal where I think from the pictures that it should be but there is nothing there just the body of the car. Is this normal for an 89 or is something missing. Below is a picture of what I have.

Oops, forgot the pciture. Here it is

http://forums.pelicanparts.com/uploa...1183068017.jpg

Your O2 sensor could be bad, your ICV may be clogged. Do a search on both of these. You will find out how to test them. Do you have Bentley's repair manual?

Good suggestion, I will try cleaning the ICV and check the idle switch as well. I do have the Bentley's manual.

I foudn what happened to the test plug, it must have come loose from the flange and fell behind and got wedged up under the flange upside down. Whew, was worried thinking I had something extremely strange.

Any one have an idea on what that large black connector plug is?

vacuum leak or mixture problem.

I recently had the same problem. My P car mechanic put a CO2 meter on it and adjusted it. Now it's gone.

using a mirror I was eyeballing around and noticed that on the back of the throttle body there is two wire plug connector that I has nothing connected to it. Should there be something connected here? I cannot find anything about it in the Bentley manual. Cannot really get a picture of it either due to its location but it is dead center in the bottom back of the throttle body.

There are no wire connectors on the back of the throttle body, but there are a couple of vacuum connectors. One goes to the air valve that's over by the oil tank, the other loops back. Under that is the vacuum connection that comes out and splits off to the fuel pressure regulator and the fuel damper.

As for the plug, doesn't look like anything I've ever seen in a Carrera engine bay. The diagnostic port for the DME is right by the ICV. Does it go into the factory harness or does it look like it came from the factory?

looks identical to idle siwtch connector. Two blade connector sitting right in the middle on the back bottom of the throttle body. Wish I could get a camera back there to take a photo. Tried using the mirror to look around but I cannot see anything cables laying back there disconnected that would plug into it. Also cannot find a diagram that will show me that.

I will try a little harder to get a picture.

Here are the pics as best I can get (actually better then I thought), hopefully this helps.

http://forums.pelicanparts.com/uploa...1183167138.jpg

and another from the camera by the firewall facing toward the back of throttle body



http://forums.pelicanparts.com/uploa...1183167290.jpg

# on front of Throttle Body is 930.110.530.0R. Doesnt match pelican's throttle body part number for an 89. Cannot seem to find anything on that part number doing general internet searches.

Anyone have any thoughts on the plug a the top or on the throttle body?

I just looked at mine (an '84) and found two small vacuum hoses attached. It's definitely the same port you showed. Maybe on the later cars (yours), the vacuum is converted to an electrical signal right there and sent to wherever it's supposed to go. In my car's case, I can't really tell where the vacuum hoses are going. Maybe they lead to a couple of transducers further down the line.

Sorry I can't be of any real help other than to offer a comparison to an older ('84) Motronic vs. yours.

Thanks for taking the time to check that Scott. It is puzzling as I have looked at all the part numbers and diagrams I can find for 3.2 carreras and across all years they show the same throttle body.

Noticed all this while trying to hunt down a minor erratic idle. Now I am just curious to know exaclty what this throttle body plug is for, and if it actually should be connected to something.

You're welcome. By the way, I just searched my Porsche P.E.T and found no match for the number you provided. I am stumped.

Interestingly enough however, is that the parts diagram shows that piece that screws into the back of the throttle body (not with an electrical plug, however) and calls it a thermo valve, part number 930-207-231-00. It has a small tube protuding from it which connects to a small hose. That hose leads to an Air Valve (930-207-227-02). Find that Air Valve and see if it has a small diameter vacuum line attached to it (the Air Valve will also have a large diameter hose attached to it. Discount that one). If it does, trace it back and see where yours is attached. If it doesn't, maybe the thermo valve simply sends an electrical signal to the Air Valve instead of an air or vacuum signal.

Just something I would do.

Check these threads out for good info on the throttle body, AAV, etc:

http://forums.pelicanparts.com/porsche-911-technical-forum/244965-911-3-2-carrera-vacuum-hose-disconnected.html
http://forums.pelicanparts.com/porsche-911-technical-forum/322393-engine-bay-buzzing-noise.html

jbrand54,
Sorry I can't offer you any opinion but I jump in because I do have similar problem once in a while., most of the time when the car get hot, stucking in traffic. Rarely it happens right on start. I also have the black rounded plug (unluged) as shown on your first pic. It's laying under the rear aluminum relay panel. And my car is also a cab.
If you can find any info, fix on this problem, please update.
Thank you.

Thanks again for the input. I had been looking in the diagrams on that thermo valve. Shame its so difficult to really dig around back there. I have made up my mind that soon I think I will at least partially pull the throttle body so that I can better inspect the back. See what exactly is hooked up as and anything that is not that looks like it should be.

I have come up with an idea for what the plug is in my first photo. Could it be part of the cruise control? 88-89 had a different cruise control and looking at the diagram below that looks a lot like the plug-

http://forums.pelicanparts.com/uploa...1183301090.jpg

It's in the right location for Cruise Control. That was my first thought, but the 8 pin connector didn't jive with what I know as a Carrera CC, so I didn't say anything. I didn't know they changed the unit in 88.

I also have that plug unplug and my cruise control also doesn't work, but where does that plug whould plug into? There was time I dig around that whole area but couldn't find anything look even similar.

rnln, your problem sounds just like mine a couple of years ago. My problem ended up being that the idle mixture and base idle speed were out of adjustment. I took it to Hergesheimer and they hooked up a Gas Analyser to check mixture. They found both adjustments were incorrect and adjusted them to spec. Problem solved.

Many times the idle mixture and idle speed have been tampered with at some point and thrown off. These two adjustments both need to be perfect or the DME will have a hard time dealing with them and you'll have the problems you've noticed, especially, it seems, when the engine is hot.

The money I spent to have it done right by someone who knew what the he11 they were doing was well worth it, imo; peace of mind that it was done right. I've had no similar issues since.

Something to think about before you go off on a wild goose chase like I did and like so many of us do.

Scott,
Good info. Do you happen to remember their contact info, and maybe the person's name who did the adjustments?
Thanks Scott.

Sure do. Hergesheimer in Lake Forest. Jim is their ace mechanic. He is one of the best in the business. Mark and Laura Hergesheimer own the place and Laura is normally the one you'll get on the phone. She is absolutely a wonderful person to talk to and will set you right up. Please, tell her Scott Romanos told you to call. 949.458.7223

I plan to have the mixture adjusted properly soon when I have the time to take it in.

Mostly on the other items I just like to know what they are so I can know why they are disconnected.

I am gonna assuem the one plug is for cruise control but I will have to try the cruise control and see if it works, never have. Never been a big user of cruise control.

As for the throttle body perhaps I will just ask when I take it in for the mixture adjustment as I will probably take it to John Walker, so maybe they will have some idea or have the part number in their system somewhere.

Thanks a lot for all of your help. i will follow up if I find out what these items are for sure.

Thanks Scott, Thanks jbrand540.

Is there any "get together" this July-4? If not, maybe I'll get together with my baby and give her some new plugs and oil.