Real bad idle
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Fleet Mechanic
Joined: Jul 2004
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From: va
Real bad idle
I have an 1987 ford f150 4.9 140,000 miles. When i remove the vacuum hose to the "tomato juice can" 
it runs better, faster idle runs better. I replaced the fuel filter, added fuel injection cleaner and water remover. Spark plugs,wires,dist. cap, rotor and air filter where changed a few years ago. Throdle body and injectors where cleaned two years ago only put a 1000 miles since.The only basic tune up part I haven't ever changed is the ox sensor. Cant get the volt meter to move when checking codes, started to move then nothing. No engine check light on 87's. Can a bad Map sensor or Ox sensor can cause this? What other sensors do i have? Will get codes next. Any ideas first?? Thanks
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it runs better, faster idle runs better. I replaced the fuel filter, added fuel injection cleaner and water remover. Spark plugs,wires,dist. cap, rotor and air filter where changed a few years ago. Throdle body and injectors where cleaned two years ago only put a 1000 miles since.The only basic tune up part I haven't ever changed is the ox sensor. Cant get the volt meter to move when checking codes, started to move then nothing. No engine check light on 87's. Can a bad Map sensor or Ox sensor can cause this? What other sensors do i have? Will get codes next. Any ideas first?? Thanks<!-- / message -->
Junior User
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Mike I have an 88 150 with a 300. I did all of those things you just listed. I even had a dealership clean the fuel injectors. The thing that you need to replace is the O2 sensor. I had the exact problem with my truck.
Freshman User
Joined: Oct 2003
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From: minnesota
there is also the fuel pressure regulator. I have the 88 model, 300 6 banger... the engien would idle or try to idle between 800 and maybe 1300 rpm.
50 bucks new... little can with a vacuum hose under the intake manifold... as your looking at the engine its on the leftside of the valve cover
50 bucks new... little can with a vacuum hose under the intake manifold... as your looking at the engine its on the leftside of the valve cover
Freshman User
Joined: Oct 2003
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From: minnesota
The truck would just idle funny. never thot of looking at the tailpipe! this truck has 227,000+ miles... hehe.
I was going to check the codes and when pulling the vacuum line off the regulator I noticed gasoline! So that was the end of finding any codes. Knowing that the fuel was in the vacuum lines only meant the pressure regulator had a hole in the diaphram.
so go ahead and check the lines for hole or damage and who knows maybe the truck will give you a hint to?
I was going to check the codes and when pulling the vacuum line off the regulator I noticed gasoline! So that was the end of finding any codes. Knowing that the fuel was in the vacuum lines only meant the pressure regulator had a hole in the diaphram.
so go ahead and check the lines for hole or damage and who knows maybe the truck will give you a hint to?
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Fleet Mechanic
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From: va
Originally Posted by hambeemer
there is also the fuel pressure regulator. I have the 88 model, 300 6 banger... the engine would idle or try to idle between 800 and maybe 1300 rpm.
50 bucks new... little can with a vacuum hose under the intake manifold... as your looking at the engine its on the leftside of the valve cover
50 bucks new... little can with a vacuum hose under the intake manifold... as your looking at the engine its on the leftside of the valve cover
Is there a way to check the fuel pressure without special tools? If i let the pressure out if its bad will it build back up? Did it runs ok once you put your foot on the gas pedal about 4000 rpm, i don't dare to go for a drive .
Freshman User
Joined: Oct 2003
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From: minnesota
the fuel pressure regulator is hooked to the end of the fuel rail. there is a vacuum line running from the top of the intake mainifold down and under to the regulator.
Pull that hose off either at the multi-port or where all those vacuum lines are coming out from and see if any fuel or even if you can smell it. If there is fuel in that line then its coming from the fuel rail.
No need to release the fuel pressure off the engine. Just wait over night for the pressure to drop off the engine. that is why the fuel pump runs when you start the engine to gain that pressure.
Now if there isn't any fuel in the vacuum line then great! you have one step done when looking for the problem.
IT may be some other item on the engine. however just a sugestion on what I had to do. happy hunting...
Pull that hose off either at the multi-port or where all those vacuum lines are coming out from and see if any fuel or even if you can smell it. If there is fuel in that line then its coming from the fuel rail.
No need to release the fuel pressure off the engine. Just wait over night for the pressure to drop off the engine. that is why the fuel pump runs when you start the engine to gain that pressure.
Now if there isn't any fuel in the vacuum line then great! you have one step done when looking for the problem.
IT may be some other item on the engine. however just a sugestion on what I had to do. happy hunting...
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Fleet Mechanic
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From: va
I let the fuel pressure out of the regular, and it started right up. Still runs bad. I'll check the vacuum lines for fuel. Just checked the tail pipe not much smoke but i think it smells worse then normal.
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Freshman User
Joined: Oct 2003
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From: minnesota
yep thats normal. The pcv does that. sucks the vaporized oil into the intake for the truck engine to burn.
Head scratchin and thinkng here... I usually go into the archives on this website and look around at the other problems. I know, there is the oxygen sensor and then that idle circuit in the intake for the air...
and there are those codes to pull too. that is on here somewhere or who else is out here ... we neeed some help!
take care
Head scratchin and thinkng here... I usually go into the archives on this website and look around at the other problems. I know, there is the oxygen sensor and then that idle circuit in the intake for the air...
and there are those codes to pull too. that is on here somewhere or who else is out here ... we neeed some help!
take care
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Fleet Mechanic
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From: va
Originally Posted by Mcyktor98
Mike I have an 88 150 with a 300. I did all of those things you just listed. I even had a dealership clean the fuel injectors. The thing that you need to replace is the O2 sensor. I had the exact problem with my truck.
