I have had a 1998 XJ8 but now a 1998 XK8. Neither one had any power when just adding a little pedal to gain speed.Good power if I put it to the floor. Is this normal?

 

Sounds like the throttle cable has some slack and needs to be adjusted. On your 98, if I recall correctly, you will be able to see the throttle cable connected to the throttle body. Have a second person press down on the gas pedal completely, you may then notice some slack in the cable. If so, you will have to adjust it. During the rest of the procedure, you want that person to stay pressing the gas pedal to the floor. There's a small clip on the cable: first remove it, then pull on the cable until you no longer have slack. It may be a few notches. Re-install the clip. Go for a drive. Alternatively, you may remove the intake pipe to see where the butterfly is when the pedal is fully depressed during this procedure.

 

The throttle cable adjuster is held in place by a zip tie. With no pressure on the pedal reach your finger beneath the cable and lift up. If it is out of adjustment you will feel the slack lift up before the throttle moves. Snip the zip tie, lift the plastic block out of the slot and rotate it clockwise while after a few turns reinsert and check for slack. When you feel no more slack tuen one more rotation and then reinstall.
Start the vehicle and check that it settles to normal idle. If it does place a new zip tie around the block to secure. If it doesn't back off 1/2 turn and test again. Once you hit the normal idle sweet spot secure the block and go for a spin. You will like the difference.

 

 

Unfortunately, the procedure in the video only applies to 4.2 L cars, the procedure I gave is for the later 4.0 cars. I think avern provided the correct method for the early 4.0L cars.

 

Mine is a 2004 with a 4.2 but can attest to the fact that this adjustment makes a big difference

 

Other thing to check is your fuel trims. If they are high (above, say 5%) but not high enough for a code, the engine feels sluggish and throttle response is sort of weak. Fuel trims are checked with an OBDII tool, like a cheap ELM327 and a mobile device app like TorquePro or Dash Command.

Would not hurt to aggressively clean the air flow meter with a dedicated spray and a long-ish soak.

Other option is to jump directly ahead under the expected diagnostic of air leaks on an aging car and run a smoke test. You need to buy (or make) a smoke machine, inject smoke in the intake and look for leaks.

Best of luck, keep us posted.

 

I think you have the answer. I know the Cable slack isn't the problem. I can start giving it throttle pushing down a inch or two without hardly any gain of speed.

 

Pushing down without a gain in speed indicates cable slack in your model. Look at avern 1's post again.