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Q: My RPMs keep going up and down irregularly

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I drive a 2005 Corrola with manual transmission. I'll be cruising at maybe 4/5th gear at a comfy 2100 RMPs. But if I suddenly give a little gas, it'll immediately shoot to 4000+. Then as I'm accelerating, the RPMs will fall until it appears to catch up with itself. It doesn't lurch or make any weird noise. Normally, if I were to gas it in the same circumstance, the RPMs would just gradually rise in correlation with my speed. This problem occurs at any gear and any speed.

My car has 160000 miles.
My car has a manual transmission.

Engine surging can be caused by several issues. Typically in diagnosing these types of issues, you want to start by having your engine scanned for diagnostic troubleshooting codes. If scanning the computer doesn’t pull any codes, the best way to find the issue is with a process of elimination. You will want to find and inspect the following components. One, the mass air flow sensor, can fail or have a bad connection. If this sensor is dirty, faulty, or has a bad connection, it will send the wrong information to the computer, which will possibly attempt to overcompensate with extra fuel causing the surge.

It is always smart to then check your fuel pressure as well. A clogged fuel system can also causes surges. As you press more on the gas pedal, the computer is trying to pump and not receiving the fuel it needs. It then causes the pump to work harder until it gets what the amount of fuel it thinks it should be getting. Once the computer has realized what is going on, it depletes the amount being pumped to the engine and regulates where it needs to be. These issues are typically caused by a worn fuel pump, clogged fuel injectors, or a clogged fuel filter. If none of these is the culprit, turn your attention to the spark plugs and ignition systems. You will want to test for correct voltage and timing at each cylinder. A faulty distributor or set of wires is typically the cause of these symptoms.

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