i have a 97 f150 with a 4.2L v6. the motor has about 60,000 miles on it. it misses very badly while idiling and sometimes even dies but it mainly does this while the truck is in gear. i have done about everything i can think of to fix it. i put new plugs and wires gaped to .45, new oxygen sensors both of them and today run 3 stage cleaner through it to clean out the top half of the motor. cna anyone help me with this. the truck runs fine down the road and doesnt miss at all while driving it jsut idiling

 

Is your check engine light on? If so what are the codes? If you don't have a code reader, most auto parts stores will read them for free - I know Autozone does.

If you have a digital meter, you can check the resistance of the coil pack. Values will be in your Haynes/Chiltons manual. Could also be a vacuum leak though. Check all the lines around the PCV valve.

 

yes the check engine light is on and it is showing the oxygen sensors on bank 1 and 2 are both bad. i had theese replaced just a couple of months ago but not sure of anything else because i have hooked it up 3 times to a computer and showing the same codes but my mechanic is telling me oxygen will not make it idle rough but should run rough all the time but im dont believe what he is telling me i just think he wants more money.

 

My first guess is you have a vacuum leak somewhere, or possibly a leak in the intake plenum.

MAF sensor problem? Maybe, but I don't think so.
But, I believe you can eliminate a MAF sensor problem by unplugging the electrical connector underneath it. I believe the engine should idle fine if the MAF sensor is unplugged and it is bad.

I still lean towards a vacuum leak.

Or maybe clogged EGR ports.

 

Perhaps consider the Air Idle Control valve. I tried to clean mine but it was too far gone to help. Today I replaced the AICV with a recon unit from pep boys and the Idle improved a good deal. I'm a new owner to my van and it has 234k miles so i know i have other bugs to work out.

Prior to installing the AICV my van idled so poorly i had to put the van in neutral when stopped otherwise is was a 50-50 chance of stalling.

by the way NAPA quoted me $123.00 and pep boys was only $59.99

 

The plugs are suppose to be gapped at .054".

 

Well, I own a 1998 Ford f150 reg cab with a 4.2l. It has 208,000 mile on it been a great truck! i've had the same problem, when i crank it in the morning sometimes it idles rough. When i pull up to a red light i put it in neutral and it runs fine. So i put a new fuel filter on it did'nt help, new plugs and plug wires, cleaned the idle air control valve none of this helped at all! finally figured out it was a vacuum leak, mine was behind the throttle body bellow the (iacv) major crack, now back to 100% hope this helps!

 

I had a similar problem. Service Engine light kept coming on every 2-3 weeks. It indicated banks 1&2 running lean. The vehicle would start fine and when idling after the initial morning start, would start to run rough and sometimes cut off. After the warm-up it ran fine. I did some checking and found it to be the top intake manifold gasket. I had that replaced (along with the lower intake gasket) and it fixed the problem. I still for some unknown reason get 13.5 mpg. I used to get 16-18 mpg. But at least it fixed the rough idling.

 

my 4.2 98 ford f150 is running rough when cold not as bad when it warms up changed plugs wires and coil pack did compression test and fuel pressure test all came up good don't know what to do next please help