cold idle
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Freshman User
Joined: Nov 2000
Posts: 30
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cold idle
I am sure that this has been covered a hundred times already but I need to read it a hundred and one before it sinks in. I have a 85 Bronco with a 351W and Holly 4180 carb. She starts fine and runs at a steady 1500 rpm on cold mornings for about 45 seconds and then the idle drops as the choke opens up. It then idles very rough until I coax it out of the driveway. Even after the engine temp is up to normal, the motor will stall at a stoplight unless give it a little gas to keep it going. After about another 3 miles down the road, she runs like a dream.
It sounds like (from what I have already read about) I need to adjust the fast idle screw a bit. I guess another possibility is that the hot air deflector in the breather housing is not working (do these things make a big difference on cold mornings?). I know that it is getting vacuum but I have never seen it close. I can however, move it with my finger so maybe the vacuum motor on the breather is shot. Could this cause the above idle symptoms on cold mornings?
Any advice that you might have would be helpful.
thanks.
JM
It sounds like (from what I have already read about) I need to adjust the fast idle screw a bit. I guess another possibility is that the hot air deflector in the breather housing is not working (do these things make a big difference on cold mornings?). I know that it is getting vacuum but I have never seen it close. I can however, move it with my finger so maybe the vacuum motor on the breather is shot. Could this cause the above idle symptoms on cold mornings?
Any advice that you might have would be helpful.
thanks.
JM
Senior User
Joined: Nov 2000
Posts: 285
Likes: 1
From: sunny san diego
cold idle
JM, to check the proper operation of the heated air intake, start the engine when cold and check the position of the flap in the air cleaner, it should be closed and stay that way for a few minutes.If it remains open, problem could be no vacuum supply to servo or even a bad servo. Also, your automatic choke could be rolling off too soon. Like mine, it probably has rivits to prevent adjustment, but these can be drilled out and replaced with screws making adjustment possible.Another thing I did was by-pass the temp. sensor for the distributor vacuum advance, simply run a hose directly from manifold vacuum to distributor cannistor; made a big improvement in cold engine drivability... hope this helps.
Thread Starter
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Freshman User
Joined: Nov 2000
Posts: 30
Likes: 0
cold idle
The vacuum servo is most likely bad. the hose has vacuum, but the flap never seems to close. In the morning, I will block the flap closed and see if this will make a difference in the way that the truck warms up. If not I will check into bypassing the temp sensor.
thanks for the suggestions
thanks for the suggestions
