When I go to start my 98 cabrio the engine won't turn over, it just clicks. I tried a few more times and it started just fine for about 4 or 5 times. Now it just clicks again. The battery is fairly new and all the lights, etc work. I had the starter replaced about 9 months ago. Could this be the starter again?

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Does the engine crank over but not start?

check the voltage regulator

Could be crankshaft sensor.

Have you had the flywheel ring gear checked out for worn or broken teeth this can can stop the engine turning over

Your problem may be one of the following:
First check or just replace the fuel filter. Usually located under the car in front of the rear axle, drivers side.
Next, the fuel pump may be worn out. Usually they just stop working (running).
Next, check the fuel pressure regulator. Usually located on the front fuel rail, drivers side.
Is the vacuum line attached? Not leaking or rotted?
Also, do you smell a strong fuel odor when it won't start? May be one or more stuck-open injectors, or the coil pack is bad.
Checking these in the order listed will more than likely fix your problem.
The clicking noise indicates the battery can no longer run the starter, which also means the fuel pump won't run either.

It could be a fuel issue. How old is the fuel filter? Can you hear the pump run for a few seconds when you turn the key on? Try turning the key to ON without trying to start engine three times waiting for the pump to stop running each time. Then try to start the engine. If it starts, Its a form of Vapor lock caused by the extreme heat we have had lately, and a weak fuel pump.

If none of this works, try a new fuel filter first. From there have someone check the fuel pressure regulator and then the pump. If you are in need of a new pump, take my word for it and spend the money to get one from a Dealer, and not from your favorite parts store. Most parts store parts are made in China and they are JUNK.
Have you hooked a scanner to the computer and checked the oxygen sensor(s)? If they are bad they could lean out the engine.

Is then engine light ON? if so check for codes and if not then it has to do with fuel/air delivery.

yes their is a factory immobilisor and a dead battery can upset it quite easily ,sorry but as its the antitheft then its a dealer only job

Sound like you have a starter that starting to go out, the easy way to check it is when it only clicks have some one try to start it and you tap on the starter if it starts replace it, starter going bad.

Starter or bad connection