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Engine surges or hesitates on acceleration

8755 Views 3 Replies 3 Participants Last post by  Offrd
Hi all,
Newby here to the forum. Old time Jeeper.

I have a new to me, '99 Sport 4.0 5 speed. When I start up or just accelerate under load I get a surging of power. It's not spark plugs as there is no sputtering. It just feels like if I'm lifting the gas pedal momentarily.

Anyone have an Idea where to start looking?

Another question: Are all error codes indicated by a CEL light? Could there be codes stored without any CEL indicator coming on?
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Could be a bad (dirty inside) TPS which is the throttle position sensor mounted on the rear of the throttle body where it is controlled by the throttle shaft. That's a fairly common problem for the TPS which is inexpensive and easily changed. Cycling the gas pedal or throttle body lever 35-50 times may temporarily clean it up inside enough to help with the symptoms.
Codes are stored but you need a reader to capture them on the 99 model. I changed the TPS on mine recently to fix a surge while hwy driving, but it threw a CEL and the code told the TPS was bad. As Jerry said it's a cheap and easy part to change out.
I changed the TPS and no improvement.
I changed the Cap, rotor, and plugs and no improvement (bit they were really bad and rotor corroded)

I tried Jerry's suggestion to disconnect the front O2 sensor and see if it cleared up the stumble.

It Worked:dance:

Just disconnected the O2 sensor at the harness and drove it. It threw a CEL code but it does not stumble. Actually has more power.

I will install a new O2 sensor tomorrow.

Thanks Jerry:thumb:
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