engine stumbling @ low idle
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Junior User
Joined: Nov 2003
Posts: 69
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From: Odessa Texas
engine stumbling @ low idle
My 1997 f150 with a 4.2 liter is missing. when barely started it does fine until a couple minutes later it idles down and it misses a lot. Upon acceleration it does fine until it idles down again and it starts all over again. I dont notice missing throughout the driving speeds. Ive changed the spark plugs and wires and it still does it. what should i look for next. also when i look at the old spark plugs i dont notice anything out of the ordinary. I did replace with Motorcraft Plats. I was advised to check the IAC valve, so I replaced it and reset the comp and it still does it. Ive also replaced the fuel filter but to no avail. There is no check engine light to see what the prob is. Its so weird it only does it sitting on idle. It goes up and down and sometimes wants to stop. I need advice on what to check next any advice would be helpful thanks.
Freshman User
Joined: Sep 2006
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Does anyone hear a sucking sound?
Pop open your hood, and take a listen when it's at idle stumbling, then rev her up and see if you can hear a sucking sound. It sounds to me like you've got a vacuum leak. Check the connections around the plenum, the two PCV connections are most suspect, and the brake booster line isn't much better.
The PCV lines go from the valve in the wayy back corner (looking at the engine, left side, rear of the valve cover) under the heater hoses, and is a little hard plastic tube that goes all the way up to a little rubber nipple right behind and under the throttle body. There's another breather that goes from the pcv located right by the oil filler cap over to the rubber intake hose.
The brake booster line is on the right side, and is pretty much out in the open.
There's another connection on the left side, a port right off the side of the plenum (I think it's for the MAF, but don't quote me)...
Good luck,
~Cerberus.
The PCV lines go from the valve in the wayy back corner (looking at the engine, left side, rear of the valve cover) under the heater hoses, and is a little hard plastic tube that goes all the way up to a little rubber nipple right behind and under the throttle body. There's another breather that goes from the pcv located right by the oil filler cap over to the rubber intake hose.
The brake booster line is on the right side, and is pretty much out in the open.
There's another connection on the left side, a port right off the side of the plenum (I think it's for the MAF, but don't quote me)...
Good luck,
~Cerberus.
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Junior User
Joined: Nov 2003
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From: Odessa Texas
Great advice!!! i checked for a vaccum leak and i heard a strange hissing noise and finally i found it. Its right under the plenum ( i guess thats what its called) and rns to the passenger side valve cover towards the rear. Boy thats gonna be a chore to get there. One stupid question what is that hose called?
Postmaster
Joined: Aug 2001
Posts: 4,532
Likes: 5
From: Trussville, Alabama
Sounds like the PCV line:
Positive Crankcase Ventilation
THE PCV line takes waste gas from inside the engine and dumps it back into the intake stream to burn the waste gases along with the fresh air charge.
Glad you found it.
Positive Crankcase Ventilation
THE PCV line takes waste gas from inside the engine and dumps it back into the intake stream to burn the waste gases along with the fresh air charge.
Glad you found it.
New User
Joined: Jun 2006
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now the 97 has a habbit of the intake manifold gasket failing and letting coolant enter the intake runner and causing big problems if not fixed. let the truck sit over night and check for a coolant smell when its first stared.
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Joined: Mar 2006
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I had the same problem as chiango, same experience at idle only mine starting shaking going through all gears at all speeds. After reading this post I went out and checked and sure enough the pcv line under the phlenum had a leak in the elbow connection. I thought I had major problems but it was a 5 dollar fix. Thanks!
Mines a 97 w/ the manual 2wd 131500 miles
Mines a 97 w/ the manual 2wd 131500 miles
New User
Joined: Dec 2006
Posts: 4
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I also had the same problem.... except it wasn't a vaccum leak. done the usual (plugs, wires, fuel filter, egr valve etc) after replacing the battery.... suddenly, it stopped missing!!! until after about a month. ???alternator going bad.... no, it was a loose ground. The thin copper band that ford uses was streched to the point that it wouldn't keep a good enough ground. After replacing the cable ends w/ regular ends, i haven't had problem 1 with it missing. (I hope that I didn't just jynx myself)
