Dippy Idle - '83 944 N/A
10-08-2004, 08:56 AM
#1
Three Wheelin'
Thread Starter
Join Date: Mar 2004
Location: Macungie, PA
Posts: 1,604
Likes: 0
Received 0 Likes
on
0 Posts
Dippy Idle - '83 944 N/A
About a week after I put my 944 back together (head/belt job), the idle starting getting a little "dippy". It idles at 1200 rpm most of the time, but sometimes it will idle at 1000 rpm. When the idle is at 1000, everything is okay. When at 1200, it will begin to dip to 700-800, then back up to 1200, hold for 5-10 seconds, then dip back to 700-800, back to 1200, etc, etc. If the cooling fans come on, the idle stabilizes at 1000 and does not dip. I have checked the intake boot and looked for obvious vacuum leaks, and did not find any. The cap/rotor are good, as are the wires. The plugs are older platinums. The car has 56,800 miles on it and was very well kept. It drives very well otherwise. I get about 250-260 miles on a tank of 89-91 fuel with "spirited" driving at times. There is some soot in the exhaust tip, but this could be from normal driving. I drive the car a minimum of 15 miles at a shot, usually more.
Any ideas? Thanks!
Any ideas? Thanks!
Last edited by Uranium-235; 10-08-2004 at 02:44 PM.
10-08-2004, 02:55 PM
#4
Pro
Join Date: Feb 2004
Location: KC
Posts: 579
Likes: 0
Received 0 Likes
on
0 Posts
Does it do this "dipping" action on a cold start? On a warm start? You said that when the fans come on it returns to 1000. Does it do this instantly when the fans come on? Or does is it slowly work its way back down.
10-08-2004, 04:32 PM
#5
Three Wheelin'
Thread Starter
Join Date: Mar 2004
Location: Macungie, PA
Posts: 1,604
Likes: 0
Received 0 Likes
on
0 Posts
It does not do this on a cold start, but it will do it after it has warmed up. When the fans start, the engine loads up a little (due to the electrical load?) and the idle stays constant. I know the idle should be 900, unfortunately I did not get a chance to drive the car much before losing the roller/head. I agree that it sounds like a vacuum leak, but this behavior is not constant. It has been doing it more and more, indicating a worsening situation (to me, anyway). I have checked easily accesable areas for vacuum leaks, including the intake boot, are there any areas known to leak that may be harder to get at?
10-08-2004, 07:41 PM
#7
Race Director
early cars do not have an idle stablizer valve. There is valve under the intake however that controls cold idle. It serves a similar function as the idle stableizer valve, but is much simpler and uses heat to contol is operation.
Trending Topics
10-10-2004, 09:30 PM
#8
Three Wheelin'
Thread Starter
Join Date: Mar 2004
Location: Macungie, PA
Posts: 1,604
Likes: 0
Received 0 Likes
on
0 Posts
The idle seems to be rather constant regardless of cold or hot. I checked everything again, removed and retightened the intake boot, now it idles around 1100 and hasn't done the "dippy" thing again, but it was kind of intermittant anyway. I still have not found any vacuum leaks.
How would I troubleshoot the idle control on my '83?
How would I troubleshoot the idle control on my '83?
10-11-2004, 12:49 AM
#9
Rennlist Member
If there is some soot from the exhaust pipe underneath the rear bumper, the car may be running rich. Check for an operative oxygen sensor. Very low miles for the fuel pressure regulator to have gone bad, but then again, these cars are getting old and it could be the cause of the sooty exhaust and erratic idle.
10-12-2004, 09:07 AM
#10
Three Wheelin'
Thread Starter
Join Date: Mar 2004
Location: Macungie, PA
Posts: 1,604
Likes: 0
Received 0 Likes
on
0 Posts
Okay, an update...Looked again for vacuum leaks, found none. Checked operation of auxiliary air valve, has proper voltage and resistance and appears to be closed when fully warmed. Coolant sensor is operating properly. O2 sensor...Bingo! Disconnected it, the cycling idle stopped, but still high. This morning, checked the O2 output, its low by an order of magnitude. So I guess its time for a new O2 sensor.
10-12-2004, 01:27 PM
#11
Burning Brakes
Join Date: Feb 2004
Location: Toledo and Cleveland, Ohio
Posts: 1,152
Likes: 0
Received 1 Like
on
1 Post
Originally Posted by M758
early cars do not have an idle stablizer valve. There is valve under the intake however that controls cold idle. It serves a similar function as the idle stableizer valve, but is much simpler and uses heat to contol is operation.
