Hi

If I manually go and open TB with my hand I can open it wide open but if I press the accelerator pedal to the floor, it doesn't open throttle complete in fact it's around 60% to 70%.
also i have checked there is no slack in the pedal.
What should I do?

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Is your pedal arm bent ? What about something like a floor mat or carpet stuck under the gas pedal ? If you have no slack, I can't think of any other reason why you cannot get the throttle blade fully open.

 

Also inspect cable for a kink.

 

Of the 7 civics I had, I had one civic LX that had a bent pedal arm assembly. Mine was so bent when I got the car id estimate it only went to 30% throttle

Check the pedal assembly out, its probably bent. I was never able to get mine to stay back where it needed to be so i got a replacement pedal set from the junk yard

 

I thought all your threads were consolidated. Is there slack in the cable ? They can stretch . You can adjust them sometimes if so . Slack at the manifold/ throttle body.

 

They were, doesn't stop creating a new thread.

In this case, this issue isn't car specific so could prove helpful to others by being a separate thread by itself with the possible fixes.

 

You probably have the wrong throttle cable and its too short.