Magento – Checkout: remove item from quote but keep in cart

In the end the best option seems to be creating an event listener for sales_quote_item_collection_products_after_load to remove the products from the collection. This in turn causes the quote item to be marked for deletion, which in turn updates the database when the quote is saved. As far as I can tell this is how a quote item is removed when a product is disabled.

As per as checkout_cart_product_add_after event.There are two parametera can be fetch from this event.

Your main issue with current quote items fetch.Need to use Event paramete for getting Quote Items

 Mage::dispatchEvent('checkout_cart_product_add_after', array('quote_item' => $result, 'product' => $product));

One is current quote item

$CurrentQuoteObject=$Observer->getEvent()->getQuoteItem();

and current cart product

$CurrentProObject=$Observer->getEvent()->getProduct();

Get Current Quote object from Event params:

$QuoteObject=$CurrentQuoteObject->getQuote()

It is better idea to fetch Quote from event parameter which give the update quote.

code:

   $items = $QuoteObject->getAllItems();
    foreach ($items as $item) {
        if ($item->getProduct()->getId() == $productId) {
            $itemId = $item->getItemId();
            $QuoteObject->removeItem($itemId)->save();
            break;
            }
        }

You can get quote item product by using $item->getProductType().$item field value take from sales_flat_quote_item table at Db