shaking idle
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Junior User
Joined: Sep 2007
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shaking idle
i have a 92 f150 5.0 and i dont know what to do with it it doesnt idle right it has a shaking idle and somewhat of a miss.and driveing down the road it has a little jerk like a sudden miss.i have replaced the plugs ,wires, air charge sesor , and coolant temp sesor ,and checked vacuum lines and bloked off egr.what i dont understand above idle it run very good.
Senior User
Joined: Jun 2003
Posts: 238
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From: Virginia
check the codes. That's always the first step. there might be something stored in the computer that could point you in the right direction.
It could be the IAC. that makes the idle go wierd. My ride had a bad battery ground that would cause crazy bucking at 35mph or higher.
But, check the codes and see if you get anything from that first.
It could be the IAC. that makes the idle go wierd. My ride had a bad battery ground that would cause crazy bucking at 35mph or higher.
But, check the codes and see if you get anything from that first.
Elder User
Joined: Jun 2006
Posts: 805
Likes: 3
You said you checked all the vacuum lines, but have you verified you have good vacuum at the intake? Put a gauge on the plenum, and make sure you have at least 18 inches vacuum. Your symptoms sound familiar, and my EEC never threw a code. It just compensated for the leak, and I got poopy fuel mileage and rough idle, and random sputter under load. (sound familiar?)
Two different dealers gave up on it because they couldn't find it with a mouse and keyboard. I found it with a bottle of propane and a torch (unlit). Check out my gallery to see what I found. This may not be your problem, but certainly exhibited the same symptoms. Disconnect all vacuum lines except the MAP and FPR, and cap off all the nipples. Don't forget the Vapor Cannister tube right between the venturis on the throttle body. That one is a great place to put the vacuum gauge while your testing because it's the simplest vacuum circuit, and the last one you "need" for emissions. Loosen the EGR valve, and use the gasket as a template to make a blocking plate from a steel soup or coffee can to block off the EGR. Just cut the holes for the studs, but not for the exhaust gas ports. Put the EGR back on with the plate in place. Pull the PCV out of the valve cover at the back, and plug that hose. Start the engine, and check the vacuum. If it's less than 18 inches, you probably have a leak at the plenum or lower intake. If it's more, count your blessings, but get ready for a drawn out search. Hook the hoses back up one at a time, starting with the brake booster. Keep checking the vacuum as you reconnect each hose. When it drops, you just found your leak. I'm not saying it the plenum gasket every time, but this is a common failure on the 5.0. You'll probably find that no single cylinder is the culprit with your idling miss, but more likely will find that at least two cylinders will be contributing. A compression check is anything but quick, and requires pulling all spark plugs if you don't want your battery to cave in. As for checking the injectors, if anyone can tell me how to do the right bank without removing the plenum, I'd be interested to see it in pictures. So, if you do find a plenum leak, go ahead and get new o-rings for the injectors and put those on while you have the plenum off for a new gasket. This is also a good time to clean up the throttle plates and the IAC. If it gives you a warm fuzzy, throw in a TPS while you have the throttle body off too.
More often than not, the injectors foul open, or leaking, but this is not to say they can't get plugged up with crud. Leaking is an easy problem to diagnose. Hold the throttle on the floor, and try to start your engine. It should not start. If it does, you have one of two problems. A fouled (leaking) injector, or a leaking fuel pressure regulator. The latter is most often accompanied by black smoke and rich smelling exhaust. Pull the vacuum line between it and the plenum at either end, and see if you find fuel in it. If so, the FPR is leaking.
On occasion, enough crud makes it past the filter to stop up the screens in the injectors. Normally, it would foul all 8, not just 1. The filter has a much finer filtering capacity than do the screens, and does not collapse when dirty. It simply stops letting fuel through, and the engine will starve for fuel under heavy throttle. This is noticed with a drop in fuel pressure at the rail when the throttle is opened, rather than an expected increase in pressure.
One more thing to check before going too crazy with the intake/vacuum issues. Notice in my sig, I also have the 92 5.0. The firing order on our 5.0's is 15426378. When you changed spark plugs, did you verify that the wires for #5 and #6 stay between #7 and #8 as long as possible? Keep 7 and 8 separated as much as possible when routing them from the dizzy to the plugs. This firing order is notorious for 7/8 cross-fire. Even with brand new Motorcraft 8mm wires, it WILL cross fire. Been there, done that. This was my biggest performance issue. When the truck was new, it didn't have a problem with cross fire. There is a service advisory about this problem, though. It's a good idea to keep #4 and #2 separated as well. Before you go yanking on plug wires, though, go ahead and check the wires for leakage. Put the truck in a dark place and crank it up. The darker the better, so use a flashlight to get your eyes pointed where you want to look, and then turn off the flashlight. Disconnect the under hood courtesy light, and watch closely for any stray sparking. You'll see it, but you may have to look close at places where the wires are laying against metal. If you see ANY spark at all, you'll want a good set of wires. I encourage using only Motorcraft wires. The SOOPER DOOPER MSD's and all the other gimmicky wires will do NOTHING for performance that a good set of Motorcraft wires won't do. Use something plastic to lift the wires and move them around a little, and lift them off anything they might be touching. If you use anything metal, you may find a leaky wire the hard way. That's roughly 45,000 volts coming from that coil. It may not hurt you, but will certainly make you hurt yourself. Check the coil closely too. My coil started arcing out the side to the brake booster hose which was touching the coil. Whodathunkit that the ignition would arc to a rubber hose? Trust me, it will, and will normally kill the coil if left too long. This I learned on the shoulder of I-65.
These are simple tests that cost you nothing in parts unless you find a problem. If you don't have the vacuum, fuel pressure, or compression gauges, they're good investments for keeping the truck tuned and for diagnostics on a lot of problems that the EEC simply won't flag. The EEC will tell you if there's a bad sensor. But, it won't tell you anything if it's just doing it's job of minimizing emissions and trying to keep a stoic mix in all cylinders. As for fancy code readers, save your money and buy one of the gauges listed above. Got any paper clips? Jumper STI to SIG GND on the DCL (see www.fordfuelinjection.com). Take a seat behind the wheel with your favorite beverage, and watch the CEL when you turn on the ignition. Your eyes and the CEL will do anything a fancy code reader can do for the EEC-IV OBD-I, assuming you can count from 1 to 9, and write down what you counted to. Your 92, if it has a manual tranny, will have a slightly different test procedure than it will with an AOD or E4OD. That info is available at the link above. The powertrain package will also determine if it has two digit or three digit codes. Mine has 2 digit.
Do some testing, then come back with the results if you have any trouble interpreting what you're seeing. Lots of good minds in here. Work from the simplest to the hardest.
Two different dealers gave up on it because they couldn't find it with a mouse and keyboard. I found it with a bottle of propane and a torch (unlit). Check out my gallery to see what I found. This may not be your problem, but certainly exhibited the same symptoms. Disconnect all vacuum lines except the MAP and FPR, and cap off all the nipples. Don't forget the Vapor Cannister tube right between the venturis on the throttle body. That one is a great place to put the vacuum gauge while your testing because it's the simplest vacuum circuit, and the last one you "need" for emissions. Loosen the EGR valve, and use the gasket as a template to make a blocking plate from a steel soup or coffee can to block off the EGR. Just cut the holes for the studs, but not for the exhaust gas ports. Put the EGR back on with the plate in place. Pull the PCV out of the valve cover at the back, and plug that hose. Start the engine, and check the vacuum. If it's less than 18 inches, you probably have a leak at the plenum or lower intake. If it's more, count your blessings, but get ready for a drawn out search. Hook the hoses back up one at a time, starting with the brake booster. Keep checking the vacuum as you reconnect each hose. When it drops, you just found your leak. I'm not saying it the plenum gasket every time, but this is a common failure on the 5.0. You'll probably find that no single cylinder is the culprit with your idling miss, but more likely will find that at least two cylinders will be contributing. A compression check is anything but quick, and requires pulling all spark plugs if you don't want your battery to cave in. As for checking the injectors, if anyone can tell me how to do the right bank without removing the plenum, I'd be interested to see it in pictures. So, if you do find a plenum leak, go ahead and get new o-rings for the injectors and put those on while you have the plenum off for a new gasket. This is also a good time to clean up the throttle plates and the IAC. If it gives you a warm fuzzy, throw in a TPS while you have the throttle body off too.
More often than not, the injectors foul open, or leaking, but this is not to say they can't get plugged up with crud. Leaking is an easy problem to diagnose. Hold the throttle on the floor, and try to start your engine. It should not start. If it does, you have one of two problems. A fouled (leaking) injector, or a leaking fuel pressure regulator. The latter is most often accompanied by black smoke and rich smelling exhaust. Pull the vacuum line between it and the plenum at either end, and see if you find fuel in it. If so, the FPR is leaking.
On occasion, enough crud makes it past the filter to stop up the screens in the injectors. Normally, it would foul all 8, not just 1. The filter has a much finer filtering capacity than do the screens, and does not collapse when dirty. It simply stops letting fuel through, and the engine will starve for fuel under heavy throttle. This is noticed with a drop in fuel pressure at the rail when the throttle is opened, rather than an expected increase in pressure.
One more thing to check before going too crazy with the intake/vacuum issues. Notice in my sig, I also have the 92 5.0. The firing order on our 5.0's is 15426378. When you changed spark plugs, did you verify that the wires for #5 and #6 stay between #7 and #8 as long as possible? Keep 7 and 8 separated as much as possible when routing them from the dizzy to the plugs. This firing order is notorious for 7/8 cross-fire. Even with brand new Motorcraft 8mm wires, it WILL cross fire. Been there, done that. This was my biggest performance issue. When the truck was new, it didn't have a problem with cross fire. There is a service advisory about this problem, though. It's a good idea to keep #4 and #2 separated as well. Before you go yanking on plug wires, though, go ahead and check the wires for leakage. Put the truck in a dark place and crank it up. The darker the better, so use a flashlight to get your eyes pointed where you want to look, and then turn off the flashlight. Disconnect the under hood courtesy light, and watch closely for any stray sparking. You'll see it, but you may have to look close at places where the wires are laying against metal. If you see ANY spark at all, you'll want a good set of wires. I encourage using only Motorcraft wires. The SOOPER DOOPER MSD's and all the other gimmicky wires will do NOTHING for performance that a good set of Motorcraft wires won't do. Use something plastic to lift the wires and move them around a little, and lift them off anything they might be touching. If you use anything metal, you may find a leaky wire the hard way. That's roughly 45,000 volts coming from that coil. It may not hurt you, but will certainly make you hurt yourself. Check the coil closely too. My coil started arcing out the side to the brake booster hose which was touching the coil. Whodathunkit that the ignition would arc to a rubber hose? Trust me, it will, and will normally kill the coil if left too long. This I learned on the shoulder of I-65.
These are simple tests that cost you nothing in parts unless you find a problem. If you don't have the vacuum, fuel pressure, or compression gauges, they're good investments for keeping the truck tuned and for diagnostics on a lot of problems that the EEC simply won't flag. The EEC will tell you if there's a bad sensor. But, it won't tell you anything if it's just doing it's job of minimizing emissions and trying to keep a stoic mix in all cylinders. As for fancy code readers, save your money and buy one of the gauges listed above. Got any paper clips? Jumper STI to SIG GND on the DCL (see www.fordfuelinjection.com). Take a seat behind the wheel with your favorite beverage, and watch the CEL when you turn on the ignition. Your eyes and the CEL will do anything a fancy code reader can do for the EEC-IV OBD-I, assuming you can count from 1 to 9, and write down what you counted to. Your 92, if it has a manual tranny, will have a slightly different test procedure than it will with an AOD or E4OD. That info is available at the link above. The powertrain package will also determine if it has two digit or three digit codes. Mine has 2 digit.
Do some testing, then come back with the results if you have any trouble interpreting what you're seeing. Lots of good minds in here. Work from the simplest to the hardest.
Postmaster
Joined: Oct 2006
Posts: 4,816
Likes: 1
From: Davis & Newcastle, CA
Old Paint, I'm not going to read your post because it is HUGE!! But because you took so much time to help this guy I think you deserve some rep points! I've seen that you consistently write long detailed posts for everyone in need and that's an awesome thing my friend 
EDIT: Site is still messed up and I still can't give you rep points... I'll give them to you when they fix it
EDIT: Site is still messed up and I still can't give you rep points... I'll give them to you when they fix it
Lead Driver
Joined: Aug 2006
Posts: 5,670
Likes: 12
From: Sand Lake, MI
<i>it doesnt idle right it has a shaking idle and somewhat of a miss.and driveing down the road it has a little jerk like a sudden miss.</i>
<l>
Had the same problem, only real differance was mine idled alright, almost felt like the tranny "skipped" or something at speed, more then it felt like a "miss". Well I broke down and put on a new cap, rotor, wires and plugs fixed it right up. No at the time I didn't think the stuff on it had been on it long enough to be worn out again already but it was.
Forgot to close my tag...
</l>
<l>
Had the same problem, only real differance was mine idled alright, almost felt like the tranny "skipped" or something at speed, more then it felt like a "miss". Well I broke down and put on a new cap, rotor, wires and plugs fixed it right up. No at the time I didn't think the stuff on it had been on it long enough to be worn out again already but it was.
Forgot to close my tag...
</l>
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