Low midrange power and very poor acceleration. I replaced the air filter and spark plugs, checked the wires and they looked fine. It pulls out ok and bogs down at mid throttle, then if you keep applying fuel it picks back up. It will also miss and run poor if you let off the gas slightly. When I pulled the plugs they looked like it's burning a little lean, but maybe that's normal.

Start with the easy maintenance items like spark plug wires, air filter, and fuel filter if they have not been replaced recently. A bad spark plug wire may only occasionally short out and cause these problems.Also look and see if the plugs are ok! God-Bless!

Check the following items:
1. good clean air filter?
2. no leaks in the air filter box, cover closed properly?
3. connecting hoses attached to the air box properly?
4. pcv valve working correctly?

1. Change the air filter if you don't recall the last time it was done. I record the mileage on filter with a permanent marker. Put it in a location where its visible with the air box opens. Change the air filter every 2 years or 30000 miles which ever occurs first.

2. Ensure that the two parts are aligned properly and that all the clamps and hoses all fit correctly. A good way to find vacuum leaks is to use vaseline on the ends of any poor fitting hoses. Do one at a time and you can isolate the problem hoses.

3.The two vent hoses that attach the valve covers to both sides of the air box can become loose with age. Adding some screw clamps can solve a small leak. Replace the hoses if they are hard and dried out. Also inspect the throttle body connection part of the air box for loose clamps and fitment.

4.Pcv test is pretty simple. Start the engine, open the oil cap, then hold a piece of paper over the cap. If the pcv is working the engine vacuum should try to suck the paper in. If the vacuum is weak then clean or replace the pcv valve.

If the all the above checks are good then its time to replace the front oxygen sensor.

As it is an EFI computer controlled engine the tune up will start with having the fault codes read. The ECM unit keeps the engine tuned at all times so if there are any sensors that need replacing then hat is where the tune up starts . The biggest pitfall is wasting money replacing things that are perfectly ok (plugs HT leads etc). The over sites are things that drain engine power indicating poor performance but are not connected to the engine Items include dragging brake /pads, low tyre pressures, wheel alignments, carrying unnecessary loads/ weights

MISSING CAUSED BY MANY THINGS LIKE BAD SPARK PLUGS, WEAK IGNITION COILS.STOPPED UP FUEL FILTER OR FUEL INJECTORS.WEAK FUEL PUMP.CHECK FUEL PUMP PRESSURE SHOULD BE 44 - 50 PSI.LOW CYLINDER COMPRESSION CAUSE MISSING.

How is your charging system? Sounds to me like it's not charging your battery, so it runs until the battery cannot support the ignition load.

It sounds like you have a fuel issue or spark issue. Pull your spark plugs and see how they look. If they look fine then test the fuel pump. You could try to run to fuel system cleaner through the fuel system and see if there is an improvement in idle. Could be any of the following problems,

coil
spark plugs
spark plug wires
fuel filter
fuel pump
injectors
air filter

Check the easy stuff like plugs, wires fuel pump and air filter first.

Poor gas mileage can have many roots but the best way is always to start with the ignition system. Have a look at the sparkplugs, if you've got the I6 4.0 engine it is easy to check them. Spark plugs are cheap and easy to replace. Also check the spark plug wires, be sure the connections are tight and free from rust. Check the distributor cap and rotor and if they are rusty/greasy clean them up. After you've cleaned and checked the ignition items (spark plugs, wires, distributor cap and rotor) you can move on to the fuel injection system.
Replace the air filter, it is cheap and most people overlook that single item.

When was the last time you replaced the fuel filter? A clogged fuel filter reduces power drastically which in turn affects fuel mileage.

Internal combustion engines requires 3 things... fuel, air, and spark. You do not have enough of one or more of these. If the wires and plugs are old, change them.  Air filter, same thing.  Fuel filter can also clog up with stuff after awhile. When you take a look at the air filter check where the air comes from.  It is possible a little critter has built a home and blocked the air flow (rare, but, it has happened).

Ok, there are four problem spots that i recommend inspecting the first would be the air filter.

The air filter may be clogged or dirty. this can decrease the power out put and it can also affect the idle as well. the next check point would be inspecting the spark plugs. make sue the plugs are correctly gapped and are not fouled in anyway. if they are fouled or incorrectly gapped, this will cause the symptoms you are experiencing at this time. Another check point will be the wire set(spark plug wires). make sure the wires are in good condition. remove all wires from the plugs and look inside the wire head t inspect the contacts. they should be nice and clean.if the wires are worn, replace them accordingly. the final check point will be checking the PCV valve. this valve is located Under hood, center, upper engine area, top of engine, mounted in valve cover. the testing procedure to be preformed on this specific device is stated below.


PCV VALVE TESTING PROCEDURE---

# Check the ventilation hoses and lines for leaks or clogging. Clean or replace as necessary.

# Locate the PCV valve in the cylinder head cover and remove it by pulling it upward.

# Blow into the crankcase end of the valve. There should be free passage of air through the valve.

# Blow into the intake manifold end of the valve. There should be little or no passage of air through the valve.

# If the PCV valve failed either of the preceding two checks, it will require replacement.


You will find the problem for you erratic or low idle in the areas above.

Please rate and god bless:)

missing on occasion? you changed the plugs? was it missing before are after you changed the plugs? Missing is usually caused by a spark failing to jump across the spark plug gap.i would first look for a broken spark plug insulator. Secondly, bad spark plug wires ( if you re-used them the connector might have pulled off the wire internally) also look at the coil and distributor for cracks or other problems if the plugs and wires check out ok .