rough idle
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rough idle
I have a 1986 ford 4.9 300,new carb,intake and exhaust gaskets,good compression,no obvious vacuum leaks,complete tune-up..it idles very badly.(almost sounds like a miss).runs very smooth on the road.I cant see the timing mark numbers on the timing plate(its kinda worn off)I know its 10 btdc.does anyone have a picture of the timing plate.also the egr is not holding vacuum(hand pump)so guess its bad..but I dont think this would cause rough idle..also new 02 sensor but unsure if its working....any thoughts?thanks
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No the egr is not holding vacuum(hooked up a hand pump )as I said before I cant see the timing marks/numbers on the timing bar(there almost worn off)so im guesstamating the timing.I just removed the egr and blocked it off,no difference...thanks again
MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
Well, just because you don't want to replace it, doesn't mean that ignoring it could solve your problem. I can't say for sure that it is or isn't the cat, but 20+ year old cats are definitely a possibility.
When you said there are no obvious vacuum leaks, what constitutes obvious? Did you actually check for them by spraying suspect areas with carb cleaner and listening for the jump in idle? A vacuum leak doesn't have to hiss or look obvious to cause idle problems. You do need to replace the EGR valve if it won't hold vacuum, but since there is no ported vacuum at idle, it won't contribute to your idle problems. It will, however, give you problems on acceleration and cruise speeds.
Here is a shot of the timing marks on my 300; this was taken with the belts and hoses off. This picture is in front of the water pump and drive pulleys.
When you said there are no obvious vacuum leaks, what constitutes obvious? Did you actually check for them by spraying suspect areas with carb cleaner and listening for the jump in idle? A vacuum leak doesn't have to hiss or look obvious to cause idle problems. You do need to replace the EGR valve if it won't hold vacuum, but since there is no ported vacuum at idle, it won't contribute to your idle problems. It will, however, give you problems on acceleration and cruise speeds.
Here is a shot of the timing marks on my 300; this was taken with the belts and hoses off. This picture is in front of the water pump and drive pulleys.
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yes i tried spraying for leaks but didnt hear a difference(it really runs like there is a leak though)..thanks for the pics....I will replace entire exhaust system in the future but was holding off..ok gonna go get dirty again..thanks
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