Bind variables using PHP with named placeholders

(UPD: psergey edited a bit to make more readable)
I have this PHP:

	$ts1 = microtime(true);

	foreach($iParamsArr as $key => $value)

	{							

		$stmt -> bindValue(':' . $key, $value['value'], $value['PDO']); 

	}

	$ts2 = microtime(true);

	echo 'Prepare: ' . intval(($ts2 - $ts1) * 1000) . "<br>";

	$stmt->execute();

	$ts3 = microtime(true);

	echo 'Execute: ' . intval(($ts3 - $ts2) * 1000) . "<br>";

No problem when sending this:

SELECT * FROM `V_T2` WHERE `D_T2-V7-1` = :F1 GROUP BY `S_T2` ORDER BY `S_T2` DESC

Performance fluctuating from 0.01 up to 160 s when sending this:

SELECT * FROM `V_T2` WHERE `S_T2` = :id AND `D_T2-V7-1` = :F1 GROUP BY `S_T2` ORDER BY `S_T2` DESC

It is the execute() taking time.

There is an index on S_T2, but it doesn't make any difference removing it. ANALYSE TABLE doesnt make any difference. FLUSG QUERY CASHE neither.

The issue is hard to reproduce as repeated queries with the same parameters values run fast. Only when you are change :id parameter repeatedly the problem comes after several iterations, and then persists.