Help!!! Erratic Behavior
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Drifting
Joined: Sep 2002
Posts: 2,560
Likes: 3
From: Twinsburg, Ohio
Help!!! Erratic Behavior
Hi all.
Noticed something very strange today on my 1981 928 A/T. The car starts immediately upon turning the key. Has a very nice even idle while cold.Smooth as silk. Voltmeter at 13.5.R.P.M about 1-K. When car reaches operating temperature, idle stays at about 750 for 30 seconds or so, then drops down to 500 for about the same amount of time.Then it goes back to 750 and repeating the cycle. Will do this all the time while at operating temp. When the idle drops to 500 the voltmeter drops to 12. Then it gets weirder.If the car is idling a stop sign at 750 R.P.M. A hard goose on the throttle will break the rear tires loose burning rubber. Tons of power. If the idle happens to be at 500 in the above scenario, no burning rubber, much less power. I have also noted on highway off ramps decelerating, that i can feel the same thing. Higher R.P.M.'S of course, but decelerating for 30 seconds, then not decelerating for 30 seconds. I welcome any thoughts or Ideas. Vacuum leak? Intake leak? It's got me puzzled. Thank You in advance for all help.
Noticed something very strange today on my 1981 928 A/T. The car starts immediately upon turning the key. Has a very nice even idle while cold.Smooth as silk. Voltmeter at 13.5.R.P.M about 1-K. When car reaches operating temperature, idle stays at about 750 for 30 seconds or so, then drops down to 500 for about the same amount of time.Then it goes back to 750 and repeating the cycle. Will do this all the time while at operating temp. When the idle drops to 500 the voltmeter drops to 12. Then it gets weirder.If the car is idling a stop sign at 750 R.P.M. A hard goose on the throttle will break the rear tires loose burning rubber. Tons of power. If the idle happens to be at 500 in the above scenario, no burning rubber, much less power. I have also noted on highway off ramps decelerating, that i can feel the same thing. Higher R.P.M.'S of course, but decelerating for 30 seconds, then not decelerating for 30 seconds. I welcome any thoughts or Ideas. Vacuum leak? Intake leak? It's got me puzzled. Thank You in advance for all help.
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Joined: Jun 2000
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From: Insane Diego, California
My guess would be bad ground points leading to low volage getting to the coil and/or a bad coil.
Do a search of the archives here for 'ground point' (no quotes) to learn more about locating, cleaning and inspecting them.
Anyone else have other thoughts?
Do a search of the archives here for 'ground point' (no quotes) to learn more about locating, cleaning and inspecting them.
Anyone else have other thoughts?
Thread Starter
Drifting
Joined: Sep 2002
Posts: 2,560
Likes: 3
From: Twinsburg, Ohio
Thanks Randy
I'll check the ground points. It could Be. And Gretch, even when the cars RPM'S fluctuate from 750 to 500 and vice versa, the idle is still smooth at either of those. No noticable miss. Coming hard from a start even at the lower RPM's, the engine is smooth, just noticably less power.
I'll check the ground points. It could Be. And Gretch, even when the cars RPM'S fluctuate from 750 to 500 and vice versa, the idle is still smooth at either of those. No noticable miss. Coming hard from a start even at the lower RPM's, the engine is smooth, just noticably less power.