3.2 idles badly... hunting

[Tspringer]

The '73 911T with a stock 3.2L that I just got idles like crap.

The car starts right up, does not smoke and generates plenty of power. When cold, it does seem to idle a bit low but the idle is relatively smooth. Once warmed up the idle is bad.... it "hunts" up and down over a range of perhaps 250 rpm in a cyclical manner.

Any ideas?

I know little to nothing about the Carrera injection system or troubleshooting it. The older engines I feel much more comfortable with, these newer ones, im a bit lost.

[CCM911]

I just had the same issue. My tech unplugged my O2 sensor, and no more idle hunt. While not the final solution, this has bought me time with which to investigate other causes.

[IROC]

I need to try this (unplugging the O2 sensor) as mine idles horribly also.

[Joe Bob]

The Motronic needs an 02 sensor to work correctly. It's prolly worn out and needs replacement.....

[gregwils]

What about the idle control valve? A dirty, clogged, or otherwise bad icv could cause similar symptoms. You can clean it with carb or brake cleaner and see if it has an impact. If so, it may be fine for a long time, or it may start behaving badly again. If it repeats, I would replace it.

[andyt11]

Also check the micro switch on the back of the throttle body. If it doesn't get clicked down when the throttle is off it causes issues with idle.

[PatrickB]

Originally Posted by Joe Bob

The Motronic needs an 02 sensor to work correctly. It's prolly worn out and needs replacement.....

+1! Temp fix only, as your gas mileage will be cut in half!

Also, if you haven't already, get a Steve Wong Chip - 911CHIPS - Performance Chip Tuning for the Porsche 911 This will improve EVERYTHING! Power, driveability, idle, and MPG's!

[andyt11]

I'm sure a SW chip will be awesome, but I'd still recommend getting the car running right stock before you introduce something new into the mix.

[Drisump]

I have an 85 Euro...don't know if that matters but after four years of driving, found the O2 lead had been cut....runs great, 25 mpg (US) on the highway!? I haven't dealt with it, seems that there is no need. Cheers

[crashr]

Drisump, I didn't think Euro engines had 02 sensors?

[Tspringer]

I forgot to mention, the engine in my car is a Euro spec engine.

I hope to get a chance to play with it this weekend and I will try some of the suggestions here and post back the results.

[crashr]

I had the same problem with my euro spec engine. I am still struggling but for me there were multiple issues. I would take a look at the metal/rubber connector that comes off the intake elbow. It goes to the brake booster which for a 73 you should have blocked off. Mine was cracked and was a major source of air leaks which is one of the main symptoms of a hunting idle. Once you start to rule out all possible air leaks then you can start to take a look at the mixture. If you are running too rich you will also be suceptible to a hunting idle.

I fixed all the issues and no longer have the hunting issue, although I still get a bit of sub dipping at times. I am wondering if it has anything to do with the fuel pressure.

If you search by my name you will see a number of threads as I worked through the issues.

[Drisump]

Originally Posted by crashr

Drisump, I didn't think Euro engines had 02 sensors?

I definitely have one, but since I have only the NA Bentley manual, I don't have anyway of confirming your theory. Perhaps when the car was brought in, when new, they had to install one to conform to regs. Maybe that's the reason that it seems to have no effect on my cars performance (the DME doesn't need the info).... LOL. To the OP: Vacuum leaks are often the problem with erratic idling. What does the car do when the oil tank top is removed? If no leaks are found, you may want to try a new idle speed control valve. BTW do you have an O2 sensor? Cheers

[Tspringer]

I am going to have to dig out my manual and do some more research as I know nothing about the 3.2 injection system. IE - where is the O2 sensor?

Anyone have any links or diagrams that show all the key working parts of the 3.2 injection system?


Terry

[Drisump]

Mine is on the drivers side exhaust. You can't miss it, it's an electrical probe inserted in a boss on the drivers side.

[hcoles]

subscribed - I have hunting after start up when car has been sitting for awhile, gradually been getting a bit worse with time. After running for a minute or blipping the throttle a few times usually clears it up. 89 3.2 U.S. engine

[andyt11]

yeah, you can check for vacuum leaks at the intake manifold to head gaskets too.

O2 sensor is in the top of the CAT. Comes through the engine sheet metal at the front left of the engine and connects to a plug on the car. Not so sure that is your problem though.

[Nine9six]

Any of you guyx do a search on "hunting idle"? There are no less than a billion posts on the subject...Well maybe not a billion; but close to it

[CCM911]

Originally Posted by Drisump

I have an 85 Euro...don't know if that matters but after four years of driving, found the O2 lead had been cut....runs great, 25 mpg (US) on the highway!? I haven't dealt with it, seems that there is no need. Cheers

Spot on! My mileage has not changed a bit. And my tech also has a 3.2. He unplugged his O2 sensor seven years ago. Not a big deal. My car has never run better.

[AVDCAV]

Went thru same issue, read a thread
That a guy said he re torqued his intake
Manifold. So I did it and the result was instant
And amazing. I could actually turn the intake
Bolts by hand with an extension.

Try it it's free It's 18 pounds