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Old 12-04-2000, 02:21 PM
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On my '79 300 SD my idle is too fast. My linkage and fast idle knob on the dashboard are all adjusted ok. I tried to lower the speed by unscrewing the idle screw on the side of the IP and it had no effect on slowing the idle. Turning it in increases the idle normally. I can remove the screw, and the idle remains the same. I have looked at the tips of both the idle adjustment screw(it's tip was flat), and the rack dampener screw(it's tip was slightly concave), I checked the idle adjustment screw while unscrewing the rack dampener screw. I noticed no ability to lower the idle, I noticed no change in idle upon unscrewing the rack dampener either. What other things control idle speed?

[Edited by patsy on 12-04-2000 at 02:40 PM]

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Old 12-04-2000, 03:43 PM
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Join Date: Apr 2000
Location: So. Cal
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Just a thought Patsy, but did you attempt to adjust the idle with the throttle linkage disconnected? I was thinking about this, and you recently replaced the leaky hand pump, perhaps the PO, attempted to overcome fuel starvation by tightening the linkage to increase idle speed.

Just a guess.
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Old 12-04-2000, 03:59 PM
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Mike that seems very likely, because the idle increased the moment I changed that. I suppose if the car was in fact not at idle but actually getting a little pedal pressure, then the rack dampener would not have any effect on the idle. I will remeasure all of my linkage. I did pop off some linkage that I thought might be tight to see if I could change the idle. I will check more thoroughly..
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Old 12-04-2000, 05:24 PM
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Patsy, I don't have an answer, rather a question. My 80 SD does not have this idle knob. What changed between 79 and 80. What controls my idle, a computer?
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Old 12-04-2000, 05:34 PM
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Rick, I noticed the other day that there is a difference between the '79 and the '80. I think you have a bunch of emissions stuff that was introduced in 1980. I don't know right now about your question, but I will look it up.

Mike, my vacuum shut off linkage may be the culprit. I think it is way out of adjustment now. Good call. I am going to adjust it and I'm sure my idle will be solved.

Can someone tell me if my two adjustment screw tips are supposed to be convex? It seems as though I keep reading this in other posts regarding the rack dampener bolt? Mine look like they are supposed to be flat.
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Old 12-04-2000, 07:02 PM
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You should have the idle adjustment screw with the locknut, on the side of your Injection pump. It is between the engine block. You should also have the rack dampener bolt with locknut on the back of the injection pump(firewall side). The idle knob that you do not have is the black knob on the dash board that has a bowden wire going out to the linkage. It increases the idle speed from inside the car. It is used for cold starts. I have know idea why they eliminated it. The wire ran next to the cruise control bowden wire. It hooked in to the STOP lever. You probably still have the hole. I am curious why they discontinued using it also.

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