Help Diagnosing hard starts.

[Babytank]

On my second remanned alternator and getting hard starting. Battery also just replaced with exide AGM. It seems like the idle is too low and the tach won't pick up off the needle. This condition only happens intermittently. The Charging system and check light are NOT illuminated. No messages on the dash. Test 9 voltages are good.

Any ideas?

2005 X5 4.4
68xxxmi

[Babytank]

With engine off Voltage at dash reads 12.1V.
Started 14.2V

[sew]

In what way is it hard to start? You're not explicit. Needs to crank a lot, or only turns slowly on the starter motor, or what?
Drive the car, open the bonnet, lock down the bonnet position detect button to fool the car into thinking it's closed (I use a crocodile clip underneath). Then lock the car (with the bonnet still open) and walk away until it's gone idle and then a bit (about half an hour). Measure the voltage at the charging/jump-start posts in the engine bay. What's the voltage? And what's the ambient temperature? The figures should show if you have a battery issue (new batteries can be duds). Wait a few hours and re-measure the voltage. It's not accurate but it should give you a good idea if you have a leak. It shouldn't have dropped much between your two readings... You can get charts on the Internet to give you an idea of what the voltage at rest should be for your battery type and ambient temperature at various states of discharge.

[Babytank]

In OP I described a slow start. Must be below 500rpm. I just charged the battery to 12.69 under the hood and same issue.

[Babytank]

Dash still reads 12.1? Amb temp 80*

[sew]

I'm afraid I still don't understand the symptoms. What "must be below 500 rpm"? A starter motor will only spin an engine at about 200 rpm, enough to get it going so it fires. Are you saying the starter is sluggish becuase "under 500 rpm" isn't sluggish...

[Babytank]

It seems as if it's not catching. The starter is not straining.

[StephenVA]

I think the OP is trying to say the engine cranks longer than expected. Hot Cold?
I think what I would like to see is starter draw (AMPs and voltage when cranking) results.
Cyl power balance (Are all the cylinders firing and contributing to output)
Compression results

These are only to establish a baseline of engine starting and running condition. Slow idle condition has many contributing parts/conditions.
IAC, ISM, TPS, throttle body issues, injectors with low / poor patterns, Etc, etc as well as mechanical contributors. Let eliminate a few issues with some base lining.

If the CPS signal is weak, then the engine "Hunts" for the firing order and where and when #1 cyl and #3 are at top dead center. The engine will not fire as it has no idea which cylinder to fire off. The CPS sensor tells the Engine control system when the cylinders are at TDC and then it fires off a primary signal to the corresponding coils. If the signal is weak the engine will continue to crank until the signal is read.
Diagnostic software will display these signals on cranking.
Makes sense?

[sew]

Have you got diagnostics to get any fault codes. IMX if the starter is turning fine then the usual cause of not firing would be crankshaft position sensor.

[Helihover]

Maybe if you posted a video of you starting your vehicle, it could help. I'm confused too.