For the last 2 months, my 2006 Honda Accord I4 Automatic has had trouble starting up, no matter hot or cold starts. 

About 25% of the time, it works perfectly - fast cranks and fires up right way.

Sometimes it will crank very slowly and the engine will barely start, but it does start.

Finally, sometimes I will turn the key to the 3 (start) position but will only hear a click. I'll turn it back to 2, then try again and it will work.

A month ago I replaced the battery with one that has more CCA to help with starting. It seemed to solve the issue, but eventually the slow cranks & no cranks came back. 

This afternoon, I couldn't get the car started at all for over an hour. Battery voltage was a decent 12.6v, I turned the key, no crank & only a click. I kept doing it and sometimes the starter would turn really, really slowly but die off. When I finally got it to start, it started just like normal, as if it didn't struggle for over an hour to start. That night, I went out to see if it would start, and it started just like normal without issues.

Does anyone know what's wrong with this thing? I suspect it's the starter itself, but it's in such a bad location & expensive so I don't want to proceed with that unless I'm sure. It could be the starter cut relay or ignition switch, but the starter runs perfectly fine sometimes. Below is a circuit diagram of the starting system.

[![circuit diagram of the starting electrical circuit][1]][1]


  [1]: https://i.sstatic.net/XXOBQ.png


UPDATE: Ended up diagnosing a bit further and replaced the starter. Now starts up strong! Used this aftermarket one from Amazon: https://www.amazon.com/gp/product/B007Y85B3W/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
And remember to buy a new intake manifold gasket.

Further diagnosis:

 - Removed the intake manifold to test continuity & resistance between the starter connection (covered by a rubber boot). Found that continuity was fine, and resistance was 3 Ohms, meaning starter has no issues with getting power. Could go further with a test light and try cranking to see if it actually gets power, but I didn't do this.

 - Note that on 2006 & 2007 models, the intake manifold has an intake plenum behind it, and the intake manifold needs to be fully removed in order to access the starter. It can be seen here (https://www.youtube.com/watch?v=kicrFfMIfuM). He's surprised about its existence, so the video isn't the best to learn how to take out the intake manifold. I removed everything except 2 coolant hoses, rotated the whole thing clockwise, and used a bungee cord to keep it in place. This video shows the technique: https://www.youtube.com/watch?v=_7HwvatuXZo.

 - I suspect that the starter's randomness is due to where the orientation of the armature lands in the starter. Some parts of it are damaged, so if it has to start up on the damaged part, it will struggle.