Oscillating Idle then all is ok?
05-08-2009, 08:33 PM
#1
Drifting
Thread Starter
Oscillating Idle then all is ok?
Weird thing happened today.
80 degrees out. motor fully warmed up and I am sitting at a red light when the idle starts to ocillate between 600 and 950 RPM.
After about 10 minutes the idle goes back to normal and has been fine the rest of the day.
82 Targa, o2 disconnected with CO set to 3.5
Any ideas?
John
80 degrees out. motor fully warmed up and I am sitting at a red light when the idle starts to ocillate between 600 and 950 RPM.
After about 10 minutes the idle goes back to normal and has been fine the rest of the day.
82 Targa, o2 disconnected with CO set to 3.5
Any ideas?
John
05-09-2009, 08:12 PM
#2
Drifting
Thread Starter
Put another 120 miles on the Targa with a mix of highway and slow traffic in 90 degree heat and the idle is now still staying at 950 as before
John
John
07-17-2009, 02:28 PM
#5
Drifting
Thread Starter
After a 100 mile spirited drive I pulled into the driveway and I left it running for a few minutes and the idle started to hunt up and down again. Took it for a drive an hour later and it was fine.
Yesterday when I got home started acting up again
I think I might have a vacuum leak somewhere and/or the mixture might be on the rich side.
My brother thinks it's a vacuum leak since it appears to be running rich at idle due to the plate moving up and down and actually be in a lean condition.
John
Yesterday when I got home started acting up again
I think I might have a vacuum leak somewhere and/or the mixture might be on the rich side.
My brother thinks it's a vacuum leak since it appears to be running rich at idle due to the plate moving up and down and actually be in a lean condition.
John
07-17-2009, 02:35 PM
#6
Burning Brakes
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Mine would do that until I got the CO set closer to 2.0, I have a '74 CIS car but without the O2 sensor they are similar I guess. I have a gas tester so I was able to watch the level drop until the idle did not hunt. Vacuum leaks are also an obvious check.
- I looked up the correct CO values from my factory service manual, the 74 cars say 1.5-2.5, the 80/81 cars (last year I have) say 0.4 - 0.8 for a range. Check before a cat and with O2 sensor unplugged. FYI
- I looked up the correct CO values from my factory service manual, the 74 cars say 1.5-2.5, the 80/81 cars (last year I have) say 0.4 - 0.8 for a range. Check before a cat and with O2 sensor unplugged. FYI
Last edited by JonH; 07-17-2009 at 10:19 PM.
07-17-2009, 10:10 PM
#7
Team Owner
I am not really sure what your brother is trying to say But I would think it is a rich condition. a vacuum leak would cause a lean condition and would cause back firing an popping if it were bad enough.
I would put he LM1 on there and lean her out. I can post my LM1 data if it would help.
Also keep in mind the FPR.
you should check your airbox closely but it just sounds like she is running a tad rich
I would put he LM1 on there and lean her out. I can post my LM1 data if it would help.
Also keep in mind the FPR.
you should check your airbox closely but it just sounds like she is running a tad rich
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07-17-2009, 10:52 PM
#8
Drifting
Thread Starter
Iceman,
We're going to check for vacuum leaks first and airbox, FP then move onto the mixture setting.
Also read somewhere that a leaking cold start valve can cause a rich idle.
I'll find out tomorrow morning.
John
We're going to check for vacuum leaks first and airbox, FP then move onto the mixture setting.
Also read somewhere that a leaking cold start valve can cause a rich idle.
I'll find out tomorrow morning.
John
07-18-2009, 02:13 PM
#9
Instructor
My mechanic told me there are a number of variables that can cause oscillating idle. Several sensors as well as fuel pressure. It turned out my problem was a motor mount bolts. They were backing out and changing the angle of the motor. This put a bind on the engine transmission connection and the sensors were reading this as a load on the motor. I was lucky. It was an easy fix that saved big problems. It also put the exhaust exit pipe in proper alignment.
07-18-2009, 03:18 PM
#10
Drifting
Thread Starter
Well we checked for leaks, none
CO has not changed since it was last set 4 years ago
FP is fine
of course after I drove 20 miles to his house idle was rock solid at 950
Then...........almost home I got stuck in traffic and it started up again this time only fluctuating about 100 RPM for about 30 seconds then smoothed out.
Batman, I'll check the motor mounts and sensor connections.
Wondering mabye if something in the WUR is sticking or a spark plug is fouling.
John
CO has not changed since it was last set 4 years ago
FP is fine
of course after I drove 20 miles to his house idle was rock solid at 950
Then...........almost home I got stuck in traffic and it started up again this time only fluctuating about 100 RPM for about 30 seconds then smoothed out.
Batman, I'll check the motor mounts and sensor connections.
Wondering mabye if something in the WUR is sticking or a spark plug is fouling.
John
07-18-2009, 05:48 PM
#12
Drifting
Thread Starter
07-19-2009, 11:25 AM
#13
Burning Brakes
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Isn't there an air valve or something on passenger side that can impact idle? I recal reading something about if you get a hunt for idle at start up, it's likely a clogged cold air valve or something like that.(sorry my terminoligy is off). My 80 sc hunts for idle for almost 60 seconts to 3 minutes when i start it up cold but then it never does it again.
Tom
Tom
07-19-2009, 05:38 PM
#14
Drifting
Thread Starter
Tom,
The idle only hunts randomly at full operating temperature during some stop & go traffic.
Today it is idling fine except for a few times slowing down fo traffic it would rev up and down only 50-100 RPM for a few seconds and then stabilizes.
I am going to lean it out a tad and see what happens.
John
The idle only hunts randomly at full operating temperature during some stop & go traffic.
Today it is idling fine except for a few times slowing down fo traffic it would rev up and down only 50-100 RPM for a few seconds and then stabilizes.
I am going to lean it out a tad and see what happens.
John