Will Mucinex (guaifenesin) d help with asthma symptoms?

Not much. Mucinex (guaifenesin) d helps to thin out mucous and decrease congestion. Asthma symptoms of wheezing and shortness of breath will not improve with Mucinex (guaifenesin) alone. Usually an inhailer to open the lung passages is required to improve asthma symptoms. .
Maybe maybe not. Though products like mucinex (guaifenesin) can reduce mucus production which is part of the asthma scenario, preventing mucus production in the first place is more important. This can be done by using your controller inhaler regularly. Unlike rescue inhalers, controllers must be taken on a routine basis to have a beneficial effect. Part of this is reducing mucus. Good Luck.
A little. Mucinex (guaifenesin) thins out mucous, aiding the patient to expel excess. However asthma symptoms are a result of constricted inflamed bronchi, and Mucinex (guaifenesin) is neither an anti inflammatory nor a bronchodilator - therefore being ineffective in relieving asthmatic symptoms.