Hello I have a 99 escort that has been acting up for a couple days. It idles fine, but when I hold press down and hold the gas pedal, the engine revs in waves. The RPMs of the rev is proportional to how much I press down, but the pulse of the wave is pretty much the same. I hold down the gas, and every second or so the engine revs up, then down, then up again...as long as I hold down the gas. It's bizzare. Then when I take my foot off the gas...it idles fine. Yesterday on the way home it drove fine. sputtered for a mile or so, then started with the pulsing rev. So I pulled over. When it's pulsing the car won't move. While waiting for a tow truck, I sat idling with the AC on for about an hour. Turned the car off, then back on, and it ran fine for about 15 miles. Then, at a light, the problem started back again.
I managed to get to an Auto Zone and they ran a diagnostic on it. I don't remember the code number (P something), but is said something like "bad mix". The guy at Auto zone said it sounded like a bad Oxygen sensor. Apparently the escort has 2 oxygen sensors, so they sold me the front one that fits into the manifold just behind the fan. The car ran fine on the way home. I swapped out the Oxygen sensor, and it ran fine around the block last night. So I thought it was fixed. Then first thing this morning....it went right back to the pulsating rev.
I thought about looking into getting the "other" oxygen sensor, but I hate to just keep guessing, and spending tons of money replacing random parts.
I'm hoping maybe someone has seen this and had luck fixing it. Anyone have any suggestions?