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Recurring issue with cold idle behavior


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Fords4Us

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Ford Ranger
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Hey everyone. I've got a recurring issue with my Ranger's cold idle, and it has continued despite a lot of attempts to fix it. Basic behavior is this:
1. cold start any given day, let it warm up for 2-5 minutes (the colder it is outside, the longer I let it warm up), drive away.
2. first five minutes of driving is fine. Engine is on standard high idle when I put in the clutch, and idles normally. Engine temp gauge is working up through the "low normal" range.
3. The next five minutes' worth of driving, all bets are off. Sometimes the idle runs super high (higher even than normal driving RPMs), or it's so low it almost stalls out. When it's high, sometimes I can tap the gas pedal to kick it off the high idle setting on the carb. Other times that doesn't work, and it sticks at that really high RPM despite repeated taps on the gas pedal. This period of time corresponds to the engine temp gauge having been at normal for a few minutes.
4. That behavior continues for about 10 minutes at normal temps. Then the idle settles down again such that it runs at a nice low idle without any help from me, no tapping of the gas pedal required.

Here's what we've done so far to address the problem:
1. did the Duraspark conversion in 2015, except for the carb replacement. We kept the Motorcraft 2150.
2. Instead of merely disconnecting the vacuum lines and sensors, we physically removed all the vacuum lines and sensors, and removed the actual computer itself.
3. Looked high and low for vacuum leaks. Found several, blocked them all off.
4. Tested the engine compression (both in-cylinder compression and leak-down tests) and the engine scored surprisingly good for both. The mechanic said it was the best compression test he'd ever seen on an engine this old.
5. Finally replaced the Motorcraft 2150 with the Holley carb recommended in the Duraspark conversion guide, listed in the Tech section of this website. Got the Holley dialed in and adjusted so that it runs like a top once it's nice and warm. Also note that particular model of Holley has a manual choke. That choke is generally set to half-open for startup, then moved to the wide open position before I pull out of the driveway.

We're not sure what to check next. I'm thrilled with the power and fuel efficiency I get once it's warm, particularly with the Holley. I guess I could live with the cold idle issues, but there's gotta be a reason for it. Any ideas?
 


Fords4Us

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Joined
Dec 27, 2012
Messages
51
Reaction score
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Location
Snohomish, WA
Vehicle Year
1983
Make / Model
Ford Ranger
Engine Size
2.8L
Transmission
Manual
After posting this, I realized that the overall forum organization had changed, with a newly expanded and specific Help section. Given that, I'm going to copy this thread to the Help>2.8L forum. Please post replies there.

85_Ranger4x4 EDIT

Link here:

https://therangerstation.com/forums/showthread.php?t=179608
 
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85_Ranger4x4

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In the future just let a mod know and we can move posts around :icon_thumby:
 
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