My 99 Ford 4.2L, has a pronounced hesitation/sputter in the first few seconds of acceleration in the morning. This also happens when it has warmed up, especially going up a slight grade after a stop. I've changed the fuel filter, air filter, pcv, and plugs but not the original wires. I've added fuel injector cleaner also, but it seems to be getting slightly worse as the months pass. Any ideas?

 

Clean the mass-air sensor. Could also be a bad TPS sensor.
Jimmy

 

Go back with OE Motorcraft wires and clean or replace the IAC.

 

Thank you for your help, but the four to five second stuttering is still there in the morning. when I depress the gas pedal about a third of the way it still not getting power. I cleaned the mass-air sensor which was dirty, changed the tps sensor, it still has the same OE wires, cleaned the IAC (it was very black). When it's warm, it runs a little better but still bad in the morning. I'm thinking on buying new OE wires, and possibly IAC. Question, could there be a vaccum leak and is there a choke to take into consideration or a trip to the shop? Thanks again.

 

There is no choke. The computer uses a water temp sensor to monitor engine temp to richen it up when cold. It also uses an Air inlet temp sensor to monitor the temp of the air being sucked into the air intake.
A vacuum leak is possible, Make sure that there are no leaks between the throttlebody and the mass-air sensor. This will make for a bad running vehicle.
You might also wat to replace the PCV valve just for safe measure as well.
Jimmy

 

Use some WD-40 to spray around the intake and such;if it idles up you know there is a vacuum leak.

 

This is a good suggestion, but I would use throttle plate/carb cleaner. Anything flammable will work, but wd 40 will leave oily residue all over your engine. Just my 2 cents...

 

I would not think that a vaccum leak would be the problem. Usually with a vacuum leak the engine will idle higher than normal say 1500 rpm even when it warms up. I know my 4.2L when it starts cold idles high for bout 10 sec then drops down to normal idle speed of about 900. Going back to the plug wire idea what could be happening is that you could have a short to ground from one of your wires creating a miss fire. Check all of the wires and make sure there are no burns or cuts in it. My .02

Matt

 

ok I'll put in my .02 too and now we'll be up to .06
Sometimes a vacuum leak wont make it idle high, just rough.

 

I've had this problem with my 4.2. My problem cleared up when I changed plug wires (Bosch).

When I changed the plugs it came back a little. I reset the computer and it cleared up again. Power was up too!

4.2's seem to be tough on the factory wires. A friend of mine had the same problem. Replaced wires/computer reset and Vrrrm, Vrrm!

 

I've done everything on the list and the last thing was the plug wires, this seem to solve the problem. The vacuum test made the engine idle down, not up or to rough. How can I go about resetting the computer myself? Thanks again for all the wonderful help.

 

Seaview,disconnect your negative battery post and turn the headlight switch on for 10 minutes.Then turn the headlights off,reconnect the battery and drive it.

 

Thank you, lxman1, BlueOvalFitter, Pass The Peas, stx_V6,
Racerguy, Almost_Out_of_Hair, for all your help.

seaview.