Idle Too Low During Warm Up - '84 3.2 911 Targa (Euro)

[84porsche9113.2]

I'm new to this board, I used to be a member of one of the other porsche boards a long time ago, that was when I was fixing up my car. Since I did all the work my car runs pretty well except for the one minor problem below. So as a result I haven't frequented the boards as much as I used to. This one problem has recently been bugging me since it is there every single time I start my car and doesn't go away until I've driven 20-30 minuites.. Anyone have any ideas what it could be? I've done all the standard upgrades previously like head temp sensor, dme relay, oil return tubes, bump steer kit, etc, etc. All the major fixes and upgrades everyone who follows these boards or buys the porsche parts catalogs usually does. This particular problem doesn't seem to be that common as I've not found anyone talking about it yet, though I'm hoping maybe someone else has had a similar problem. If so maybe the solution can be put out there to help others who may have the same symptoms...

Here it goes -- my porsche idles very very low at warm up (around 500rpm) and no matter what I do, will not idle normally for about the first 20-30 minuites of driving. After about 20-30 mins of driving (during normal warm summer weather), the temperature usually hits 1/4" past the first white tick (which I think is the normal operating temperature), and then it it is like someone turned a switch on -- the engine starts to idle perfectly at 900rpm and purrs. But until that point (which I am at a loss to predict when exactly it will happen), idle is terrible. All I know is at "some" point of driving after the engine gets hot enough, the idle just gets stable and stays that way. Until of course I let the engine cool down and start it up again, it is right back to that weird and low idle.

That temperature mark seems to be the normal operating temperature, as when I am driving on a cool night it does not go higher than that point, no matter how long I drive, but when it hits that point, all of a sudden idle is perfect. It is just the warm up period right after starting and all the way until hitting that point that the idle is much too low.

I've tried everything to jumping the socket with a wire and adjusting idle, to replacing the idle valve, to cleaning it, etc. I'm hoping this is just a simple fix which I'm over looking. The fact that something about the temperature causes it to run perfectly makes me wonder if it is mechanical or electrical in nature.... Anyone have any suggestions or ideas as to what it could be or what I can try to fix it? Thanks again in advance...

[DonMo]

A couple of other things to eliminate, vacuum leaks (use fuel injector cleaner and spray around intake gaskets, they are known to leak in our year car. Next at idle, when warm, pull your afm connector off your your air box and see if the idle changes. If it does, you are still off. Get your idle/mixture set right. Last and hardes to find is a intermitently failing dme component. There is a great recent "surging post on the subject".

Oh, if you put where you live, a near by Pelican may be able to share their tools and help.

[84porsche9113.2]

Hey DonMo, thanks for your speedy reply. Anyway, just to let everyone know I may have solved the problem already. Your post gave me some inspiration to go poking around the engine again. At first I played with a bunch of different connectors hoping maybe the connections were intermittent and would be restored. Then I sprayed some injector cleaner around and nothing happened. Lastly, I removed the air filter and played a little with the barn door sensor. A while back when I removed my idle filter I noticed there was a gritty/grimy/greasy oily film in the hoses that go in/out of the idle valve. I mean it was really dirty. Like I stuck my finger in the hose and it was covered with a black gritty (like fine sand) & greasy film. I am not sure how all that stuff got in there through the air intake, except that at the time, I had been running a K&N. My only thought was if those hoses were that gritty and oily, there must be a lot of the same stuff in the 90 degree hose before the intake and in the throttle body. So what I did at the time was I used carb cleaner to clean it all out. I think I may have removed the clamp on the 90 degree elbow and sprayed in from there. I also changed back to a regular paper filter.

Anyway, this time when I removed the airbox, I sprayed fuel injection/carb clealer direclty into the air flow sensor (where the barn door is) and that seemed to do the trick! It idles much higher now even when cold. I tested it a few times when it was cold and it idles properly every time. I think the real test will be when I let it sit over night and start it up in the morning. If it still has a good idle then, I'll know the problem was solved. I'm not sure if that was safe for the air sensor (to spray directly into it) or if it needs to be a bit oiled (as it has a moving part in there). If someone knows could they let me know? So anyway, so far so good. I'm hoping it will turn out to be a permanent fix, but again, so far, so good. BTW, I never thought that would fix it. A couple of mechanics did say to remove and spray cleaner or wd40 into the idle valve, but no one mentioned cleaning out the air sensor. I wonder if that is because this is not a very common problem (but stuff in the idle valve is)?

[DonMo]

As to the AFM, cleaning it shouldn't hurt, I have had mine off the car and apart. It is a barn door, a little spray should be fine. It really is dirty in there and can use a good cleaning. I am glad you fixed it. You must have cleaned it enough where the door closed all the way and fixed your air mixture. As to taking the ICV off and cleaning it, I would. it makes a difference. I would use something that doesn't collect dirt. Silicon or something. Oil is okay but it starts a routine of routine cleaning.