My 1999 Ford 4.0 has a hard miss at driving speeds and it also has a rough idle in gear with your foot on the brake. I have changed Spark Plugs, ohmed out the spark plug wires, changed the coil pack, cam sensor, crank sensor and MAF sensor. The only code is P1151 (Hot O2 sensor) Please help!!!

Hi, 1994 4-runner hard-start after 3-4 hrs......All the above are good possibilities and should be checked.....I don't know what changing to E3 means exactly, but if it means changing the spark-plugs, it could be that the plugs are too cold or too hot ....it is probably best to stay with the factory recommended plugs ....some plugs are hot and some are cold ,in case you are not aware of it.......good luck with it....Frankie Don.

Is the check engine light on ?
Have you checked the computer for trouble codes ?
You could have one bad spark plug even with only 30k on it.
Problem could also be a dirty injector.

For engine misfiring problem check the help links mentioned below. Click the link below to go through the troubleshooting procedure :---- Engine misses and truck jumps? Hard to down shift? Issue with high gear only? http://technoanswers.blogspot.in/2012/02/engine-miss-and-truck-jumps-hard-to.html

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Bad miss at idle?

http://technoanswers.blogspot.com/2012/01/bad-miss-at-idle.html

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While stop engine idles like cylinder missing?

http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html

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Engine Misfire codes for car?

http://schematicsdiagram.blogspot.com/2011/12/engine-misfire-codes-on-chevrolet.html
Engine Misfire codes?

http://schematicsdiagram.blogspot.com/2011/12/engine-misfire-codes-on-chevrolet.html

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Misfire on cylinder 4?

http://schematicsdiagram.blogspot.com/2011/12/misfire-on-cylinder-4.html

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Oil on spark plugs and car misfires?

http://technoanswers.blogspot.in/2012/02/oil-on-spark-plugs-and-car-misfires.html

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This will help.

Thanks.

For engine misfiring problem check the help links mentioned below. Click the link below to go through the troubleshooting procedure :---- OBD-II Trouble Code P0300? http://schematicsdiagram.blogspot.com/2011/12/obd-ii-trouble-code-p0300.html
---------- Engine misses and truck jumps? Hard to down shift? Issue with high gear only? http://technoanswers.blogspot.in/2012/02/engine-miss-and-truck-jumps-hard-to.html

-----------
Bad miss at idle?

http://technoanswers.blogspot.com/2012/01/bad-miss-at-idle.html

-----------
While stop engine idles like cylinder missing?

http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html

------------
Engine Misfire codes for car?

http://schematicsdiagram.blogspot.com/2011/12/engine-misfire-codes-on-chevrolet.html
Engine Misfire codes?

http://schematicsdiagram.blogspot.com/2011/12/engine-misfire-codes-on-chevrolet.html

--------------
Misfire on cylinder 4?

http://schematicsdiagram.blogspot.com/2011/12/misfire-on-cylinder-4.html

-----------
Oil on spark plugs and car misfires?

http://technoanswers.blogspot.in/2012/02/oil-on-spark-plugs-and-car-misfires.html

----------

This will help.

Thanks.

• does the engine miss? bumps is a rythmic pattern?
• an engine miss will appear to diminish at higher rpm due to centrifical force.
• other possible problem broken or flat motor mount.
• is the idle rough in reverse?
• if not
• open hood
• start engine
• Left foot on brake (hard)
• start engine
• watch engine as you select drive
• still holding brake with left foot / throttle gas with right foot
• does engine dramatically move?
• if so replace motor mount on offending side
• if not possible engine miss or transmission problems

What kind of spark plugs did you put in it? The 4.0 litre engines in these trucks require PLATINUM spark plugs. If you put the wrong ones ( regular copper) it will miss fire and run like a bag of garbage. I had a similar problem with mine, the previous owners said "oh we changed the plugs and wires". They also changed the ignition coil not long before I took delivery. So, truck still ran like **** they said they even had to reset the inertia switch under the passenger side kick panel, everyone thought it was a fuel problem. I decided to pull one plug and volia..Wrong plugs. That also explains why they had to change the ignition coil. Hope this helps.

could be a vac leak. what are the definitions for the codes??

you might try changing the engine coolant temp sensor. could also have defective spark plugs. check the fuel filter, lines and pump.

could be a wire crossed, or it's out of time. since you used motorcraft plugs, did you set them properly to the correct gap? replacing plugs without gapping them can cause the sluggishness, out of time can cause the mis-fires and rough running.

your probably feeling a rough idle of the engine. need a tune up?

in park the engine is not loaded down, just idling at a low rpm=rough
in drive with brake on you have put some load on motor also at low rpm=rough
in drive on the road engine is at higher rpm, = smoother

generally 4 cylinder motors idle a bit rough, especially if one spark plug is not firing right or fouled or one bad spark plug wire. tune up may fix it. if it is not stumbling real bad or stalling then you can live with it.