The Dreaded Idle Mystery, Idle Me This |
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The Dreaded Idle Mystery, Idle Me This |
Apexster |
Jan 2 2020, 03:05 PM
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#1
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Newbie Group: Members Posts: 8 Joined: 1-June 18 From: Concord, CA Member No.: 22,180 Region Association: Northern California |
Looking for a little insight on the dreaded idle mysteries of a 1974 2.0 914. I've searched the archives for a couple months and tried just about everything.
Valves freshly adjusted. Compression is above 135psi and within 2% on all cylinders. Original D-jet intact with new hoses and all components tested and working. Fuel pressure tested (30-31psi from original 3 hose fuel pump). New plug wires, newly rebuilt distributor, recent fuel filter. I'm about to replace the 20 year old CHT sensor as well. The car revs smoothly and pulls very strong. Engine runs great anywhere above 1200 rpm. Problem is 3 or so minutes after a cold start it drops off the high idle and transitions to a rough idle, like it's running on three cylinders. When I spray carb cleaner in the air cleaner the idle smooths out immediately. Has anyone else come across this issue and perhaps suggest a plan of action to resolve it? (IMG:style_emoticons/default/confused24.gif) Thanks and Happy New Year to All. |
GregAmy |
Jan 2 2020, 03:48 PM
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#2
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Advanced Member Group: Members Posts: 2,311 Joined: 22-February 13 From: Middletown CT Member No.: 15,565 Region Association: North East States |
Does it ever smooth out after warm-up? If so, could be the dreaded "donut hole" of running too lean until full warm-up. The CHT richens the mixture when dead cold, but ramps down too quickly, so the D-Jet runs lean until the car is fully warmed up. It's a common discussion here and elsewhere, and short of running resistors on a switch to trick the D-Jet ECU I've not seen a solution.
Cold start valve works only during cranking (and only below ~40 degrees), so that's not it. Three minutes does sound like the AAR, but the closing of the AAR - the computer is unaware of the AAR's position - that would richen the mixture, not lean it out. So...back to the first sentence: does it ever smooth out after warm-up? Or does it continue running like that forever? |
Apexster |
Jan 2 2020, 07:53 PM
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#3
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Newbie Group: Members Posts: 8 Joined: 1-June 18 From: Concord, CA Member No.: 22,180 Region Association: Northern California |
Does it ever smooth out after warm-up? If so, could be the dreaded "donut hole" of running too lean until full warm-up. The CHT richens the mixture when dead cold, but ramps down too quickly, so the D-Jet runs lean until the car is fully warmed up. It's a common discussion here and elsewhere, and short of running resistors on a switch to trick the D-Jet ECU I've not seen a solution. Cold start valve works only during cranking (and only below ~40 degrees), so that's not it. Three minutes does sound like the AAR, but the closing of the AAR - the computer is unaware of the AAR's position - that would richen the mixture, not lean it out. So...back to the first sentence: does it ever smooth out after warm-up? Or does it continue running like that forever? I haven't warmed it up for more than maybe 8-10 minutes since discovering this issue and therefore can't answer that question, yet. I'll give that a try before installing the new CHT. I also ordered Brad's spacer and plan to test the new CHT sensor with and without the spacer. Hopefully this weekend. |
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