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Old 12-10-2017, 02:24 AM   #1
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Default Idle Problem Trouble Shooting

Went a couple pages deep looking for anything on this and didn't turn up much. If you know a thread, links are always appreciated.

1986.5 D21 V6/5SPD with ~200K miles.

God I love this truck, that being said, vacuum operated technology is annoying.

Truck starts just fine, starts and when fully warmed up hangs around 1250-1500 RPM. After a good drive when I let it sit and idle I can hear the RPM's try to drop, but it does a little bit then returns to 1250-1500 Engine sometimes stutters for a milisecond in that range when accelerating/decelerating. Engine feels under-powered, but will go through entire RPM range.

Looking for where to begin and progress with my idle issue. I figure throwing parts at it won't do much besides waste time and money. I have read that many many things could be throwing a bad idle.

Air and fuel filters replaced recently. Threw code 13 and the cylinder head temp sensor was replaced. Truck is due for cap/rotor/wire/plugs and a timing check, doing that soon. Timing belt looks good.

I am going to start with the timing/wire/plugs/rotor/cap. Beyond that, how should I approach diagnosing the issue?
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Old 12-10-2017, 02:31 AM   #2
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If its due to timing check, and cap, rotor and more I'd do those first then check back. Make sure your throttle cable isn't causing a problem either. Ive done that to myself before. Too tight and causing high idle.

If its time for a timing check just do the belt and tensioner while you are there. No need to fiddle with it more than you have to. Remember, that's a 60k mile belt on there
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Old 12-10-2017, 04:07 AM   #3
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If you're gonna do that stuff anyway then yeah do it, but have next time you pop the hood grab hold to the MAF sensor and give it a little wiggle, note if the rpm changes, do the same thing with the wires going to the MAF. that plug is known the be a bit problematic, as is the MAF sensor itself. but yeah do that other crap first.
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Old 12-13-2017, 09:51 PM   #4
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I wouldn't be afraid to throw an oxygen sensor at it.

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Old 12-13-2017, 10:37 PM   #5
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i had to do the water pump and belt on mine last month. when i was setting the timing by ear, it started that funky up and down idle when i got too far. you might was to throw a timing light on it and see where its set.
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