rough and jerking idle
Elder User
Joined: Oct 2002
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From: Marysville Wa
lol theres alot of questions on this one thread, have you all started by running the KOEO and KOER tests yet? im still trying to dignose mine, it hasnt run right ever sense that last river crossing (FI doesnt like the water)
Freshman User
Joined: Jun 2004
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I had the same problem on an 89 Chevy Cheyenne 1500. I changed the plugs, cleaned the throttle, and replaced the cylinders. The problem kept going on. It ended up needing a new head gasket which solved the problem. I don't know if that will solve the problem on your Ford or not.
Posting Guru
Joined: Nov 2003
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From: Sussex County, DE
From my field experience as a tech, I can tell you that Fords are notorious for having bad MAP sensors and yet not triggering a code. A bad MAP sensor will be worst at idle to light throttle... whenever manifold vaccum is high. The problem is, without an ociliscope, it can be very dificult to test them because they vary frequency, not voltage. You'd be looking for a square wave 5 volt pattern with a high frequency at low vaccum and lower frequency at high vaccum. A service manual can provide you with the frequencies, as I don't remember them off the top of my head. Also, make sure you are getting adequate vaccum to the MAP sensor in the first place, and if you have any doubts, run a dedicated line to the sensor and take a test drive to see if it makes a difference.
Fleet Mechanic
Joined: Jul 2004
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From: va
Checking MAP
Originally Posted by Argo
From my field experience as a tech, I can tell you that Fords are notorious for having bad MAP sensors and yet not triggering a code. A bad MAP sensor will be worst at idle to light throttle... whenever manifold vaccum is high. The problem is, without an ociliscope, it can be very dificult to test them because they vary frequency, not voltage. You'd be looking for a square wave 5 volt pattern with a high frequency at low vaccum and lower frequency at high vaccum. A service manual can provide you with the frequencies, as I don't remember them off the top of my head. Also, make sure you are getting adequate vaccum to the MAP sensor in the first place, and if you have any doubts, run a dedicated line to the sensor and take a test drive to see if it makes a difference.
Posting Guru
Joined: Nov 2003
Posts: 1,006
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From: Sussex County, DE
Unfortunately, you'll most likely need a scope. If you use a multimeter, you will only get a voltage average. The MAP Sensor switches a 5 Volt reference signal supplied by the computer hundereds of times per second, high (5v) and low (0v). The slower it switches (I.E. lower frequency) the more vaccum you have. The faster it switches (I.E. higher frequency) the less vaccum you have. The problem is, your meter can't respond that fast, so it'll read anywhere between 0v and 5v, which is pretty much useless. If you can get a scope on it, you want to set the it to 1v/Div. and 2mS/Div. and look for a clean square wave pattern that smoothly and proportionatly expands when vaccum is applied.
Fleet Mechanic
Joined: Jul 2004
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From: va
Originally Posted by Argo
Unfortunately, you'll most likely need a scope. If you use a multimeter, you will only get a voltage average. The MAP Sensor switches a 5 Volt reference signal supplied by the computer hundereds of times per second, high (5v) and low (0v). The slower it switches (I.E. lower frequency) the more vaccum you have. The faster it switches (I.E. higher frequency) the less vaccum you have. The problem is, your meter can't respond that fast, so it'll read anywhere between 0v and 5v, which is pretty much useless. If you can get a scope on it, you want to set the it to 1v/Div. and 2mS/Div. and look for a clean square wave pattern that smoothly and proportionatly expands when vaccum is applied.
Last edited by mike L; Sep 18, 2004 at 10:54 AM.
Lead Driver
Joined: Nov 2002
Posts: 9,557
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From: Concord, NC
You can test the MAP with a 6 cylinder tachometer. Voltage should be 2.5 on the blue signal wire, and 5V on the orange reference wire.
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New User
Joined: Nov 2003
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argo, i have found out that there are two different kinds voltage varrying and frequency varrying map sensors, and your can check the freq with a tach, the test goes as follows : volt cont .... with a good ground on your volt meter, and pos conected to your sig wire ( middle ) with no of vacume it sould be around 5 volt then increase steady up to 5v +-1v, then aply 20hg vacume and your voltage should drop to 1v. a similar test with a frequency varying map use a tachometer and at 20hg you should have about 200rpm
Freshman User
Joined: Dec 2003
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From: Murray, Ky
My 95, F-150 was also wanting to die at idle or crusing through a parking lot.
I t would also hiccup sometimes at crusing speed. I replaced the throttle position sensor this past weekend, and now the truck is running fine.
I bought the TPS on EBay for $14.99 + $5.00 s&h. Autozone wanted $31.99.
Clava
1995 Ford F-150 4x4 E4OD ext cab 5.8 188,000 miles
Built Ford tough!
I t would also hiccup sometimes at crusing speed. I replaced the throttle position sensor this past weekend, and now the truck is running fine.
I bought the TPS on EBay for $14.99 + $5.00 s&h. Autozone wanted $31.99.
Clava
1995 Ford F-150 4x4 E4OD ext cab 5.8 188,000 miles
Built Ford tough!
Post Fiend
Joined: May 2004
Posts: 11,289
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From: Lakewood, Ohio
Originally Posted by stubbiecatmanx1
I have a '90 5.0 L V8 F-150. When I drive the turck, i can take my foot of the gas and the truck will idle at about 15-20 MPH. How can I fix this?
you have a bad iac. replace it.
New User
Joined: Dec 2002
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Tps...
My 1995 F150 (5.0) did about the same thing, and it was the TPS. You can test the TPS with a volt-ohm meter. Cheap part to replace, too - before you start tearing down engines, or replacing harmonic balancers, check that.
This has been a remarkably reliable truck. In 110,000 miles, I have replaced the TPS, an A/C clutch, and an idler pulley. Other than spark plugs, wires, rotor, and cap (and serpentine belt) the engine is as from the factory. Even the original hoses.
This has been a remarkably reliable truck. In 110,000 miles, I have replaced the TPS, an A/C clutch, and an idler pulley. Other than spark plugs, wires, rotor, and cap (and serpentine belt) the engine is as from the factory. Even the original hoses.
Fleet Mechanic
Joined: Jul 2004
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From: va
Originally Posted by robertplattbell
My 1995 F150 (5.0) did about the same thing, and it was the TPS. You can test the TPS with a volt-ohm meter. Cheap part to replace, too - before you start tearing down engines, or replacing harmonic balancers, check that.
This has been a remarkably reliable truck. In 110,000 miles, I have replaced the TPS, an A/C clutch, and an idler pulley. Other than spark plugs, wires, rotor, and cap (and serpentine belt) the engine is as from the factory. Even the original hoses.
This has been a remarkably reliable truck. In 110,000 miles, I have replaced the TPS, an A/C clutch, and an idler pulley. Other than spark plugs, wires, rotor, and cap (and serpentine belt) the engine is as from the factory. Even the original hoses.
Thanks