5.3l low idle
#1
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I have found lots of info regarding high idle RPM, but very little about low idle, so I hope any here in the forum have some tips.
A bit history
The car is still at sellers garage, and I work on the car now and then to make it work so i can drive it back to my place.
what I've done.
Engine did not run on all cyls.
Done a compression check. (Lowest:11.4, highest: 13.2) and cleaning plugs. - No change
Made new injector harness w/new connectors.
- No change
Changed spark plugs.
- Dramatic improvement
It now runs nice and fine on all 12 cyls. (Plug cables are OK, and distributor cap seems to be almost new).
The only thing now is that the idle speed is about 550 rpm and up to 600 rpm, and drops to about 400 or so and sometimes nearly stops when put in drive or reverse.
There is no difference between cold and hot engine. I have tried to adjust the idle screw on the AAV several revs CCW, but no change.
Is there anything else to adjust?
oh, one little ting. When pressing the pedal, the engine RPM drops a bit before picking up rpm.
A bit history
The car is still at sellers garage, and I work on the car now and then to make it work so i can drive it back to my place.
what I've done.
Engine did not run on all cyls.
Done a compression check. (Lowest:11.4, highest: 13.2) and cleaning plugs. - No change
Made new injector harness w/new connectors.
- No change
Changed spark plugs.
- Dramatic improvement
It now runs nice and fine on all 12 cyls. (Plug cables are OK, and distributor cap seems to be almost new).
The only thing now is that the idle speed is about 550 rpm and up to 600 rpm, and drops to about 400 or so and sometimes nearly stops when put in drive or reverse.
There is no difference between cold and hot engine. I have tried to adjust the idle screw on the AAV several revs CCW, but no change.
Is there anything else to adjust?
oh, one little ting. When pressing the pedal, the engine RPM drops a bit before picking up rpm.
#2
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Make sure you have adjusted the throttle butterfly's correctly. Insert a 0.002" feeler gauge in TOP of the butterfly and adjust the stop screw to just touch the arm.
The AAV (Aux Air Valve) is down the back of the LH air filter there is a screw on the lower front - this is the idle adjustment.
Do these simple things first and report back if this does not fix your problem then we will look further.
Last edited by warrjon; 10-03-2012 at 05:57 AM.
#3
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Thanks.
I'll check the butterfly adjustment. did not know about that.
The linkage is firm and fine. I checked the linkage and the throttle pedestall, suspecting that the bellcrank traveled to much back (making the link go over center) in idle so that the link would close the butterfly's a bit before opening them, but that's not the case.
I'll report back when the butterfly's checked/adjusted.
I'm not sure what you mean by: "You can tell CR from a compression pressure test"
but I don't think compression has anything to do with this. The compression seems fine to me.
I'll check the butterfly adjustment. did not know about that.
The linkage is firm and fine. I checked the linkage and the throttle pedestall, suspecting that the bellcrank traveled to much back (making the link go over center) in idle so that the link would close the butterfly's a bit before opening them, but that's not the case.
I'll report back when the butterfly's checked/adjusted.
I'm not sure what you mean by: "You can tell CR from a compression pressure test"
but I don't think compression has anything to do with this. The compression seems fine to me.
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#4
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The most important thing is that the pressure does not vary by more than 5psi from lowest to highest.
Check the bushes where the cross rods connect to the linkages on the manifold that operate the throttle butterfly.
#5
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Sorry what I meant was you can not tell compression ratio (CR) from a compression test. Due to factors like valve overlap - if you decrease valve overlap the cranking pressure will increase, but CR will still be the same.
The most important thing is that the pressure does not vary by more than 5psi from lowest to highest.
Check the bushes where the cross rods connect to the linkages on the manifold that operate the throttle butterfly.
The most important thing is that the pressure does not vary by more than 5psi from lowest to highest.
Check the bushes where the cross rods connect to the linkages on the manifold that operate the throttle butterfly.
You nailed it. Thanks very much.
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I adjusted the butterfly and set the opening for 0.05mm. They where practically closed.
After adjusting, I have 790 rpm. Further adjustment I can do witht the idle adjustment at the AAV.
Also, the butterfly axel has a worn down bushing at the back end. In fact, the worn is so bad that the bushing is totally gone. Se photo.
thanks again for very good help.
Case closed!
#6
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Glad you got it sorted so quickly
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