911 Rod

Pete,
Why would it change after being set for so many years?
Would it maybe need to be cleaned?
Thanks
Rod

Peter Zimmermann

If the problem is the AFM it should be considered as a part failure, not a change. Better than a limp home mode, but still a failure. We talked to a couple of electronic guys thinking that we could get them fixed, but that would have cost more than replacement, so we abandoned thoughts of repairing them. After seeing the problem a few times (remember, we knew the overall condition of most of the cars that we maintained) we just replaced the AFM, which almost always brought the CO back in line.
Pete

phiba

It sounds to me like you could benefit from an air fuel ratio (AFR) monitor/ logger such as the Innovate LM-1. I have been studying them lately for my 78 SC, and concluded that they probably are not that useful without electronic control of fuel mixture. But for later cars (1980+), it seems like a very cool tool. You can even replace your car's O2 sensor with LM-1's, and then have the LM-1 provide the analog O2 signal to the car's computer. Innovate has an interesting forum at http://www.innovatemotorsports.com/forums/ BTW, I have no affiliation with them - I don't even own one of their devices (yet).

DonMo

I too had the hunting Carrera problem, I cleaned up my vacuum leaks (Carrera intake gaskets are notorious), had the CO adjusted using a friends Gunson and guess what, no hunting. No cost and I learned something. A wonderful thing.

J. Brinkley

having an LM1, and reading and knowing the bosch motronic book seem like no brainers. If you have these tools you can eliminate all this hunting stuff. You can know and understand the whole motronic proccess. Why it hunts, when, and how. Spending 5 or 6 hundred might hurt, but how much are you spending at wrenches and jiffy lube? time online searching? So maybe it takes two or three years to get your money's worth. When your friends find out you can charge them for setting their AFR, or trade parts for it.There are so many things you can do with a LM1, it would take pages to describe.
The bosche motronic book is almost more valuable than a bentley. Getting your car, SC or carrera or anything motronic, to idle right should be the first goal. And I mean idle and WOT switch, injectors and flow and volume, CHT and flywheel sensors, vacume integrity and AFM functions. Eduacate yourself and save up for a WB O2 controller/logger
if I seem rude it's because I just got home from 30 days of work and I'm into a couple beers.

rnln

DonMo,
Can you extend a little further on how to adjust the CO level yourself?

Thanks guys for all knowledgeable input.

911 Rod

Thanks for continuing the thread.
I didn't have time to check the car and today it's running fine.
It's almost time to keep a log on when it does it.

911 Rod

Hey All,

Here's where I'm at.

Did an O2 test and found the mixture is very rich during de-acceleration.
I replaced the head temp sensor as well.

I'm starting to wonder if my chip is just plain too rich.

Rod

scottb

Did you ever take the car to a mechanic and have the mixture checked? It's a simple fix. Easier than throwing a bunch of money at the car by replacing parts that may not need replacing.

911 Rod

Yes I did.
This is how I know that the car is running very rich when I let of on the throttle.

scottb

Maybe I'm asking the obvious here, but did the mechanic suggest how the problem might be fixed?

KC911

Which chip are you running? My hunting idle was a combination of an ICV going bad, and a vacuum leak, but it took me a while to track them down.

911 Rod

He figured it was the head temp sensor. It wasn't.

911 Rod

The chip is the unknown at this point. It is a performance chip put in by the previous owner. Can they change? I've replace the ICV.
How di you find the vacuum leak?
Thanks
Rod

KC911

If you have an "unknown" chip, then I'd eliminate that by trying a stock chip, Steve Wong's, or other "known" quantity. That wouldn't "change" on you, but you would be working with a "good" baseline to start with. In my case, after cleaning the ICV (which improved the "hunt" somewhat), and eventually replacing it (which improved it even more, but the "hunt" was still there, particularly after approx. 20 seconds of idling), I simply tightened all of the clamps a bit more, and now she idles perfectly. Good luck...I chased mine for a while before success !

Keith
'88 CE coupe