Cover - shares	3 Months Ended
	Mar. 31, 2026	May 15, 2026
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes
Amendment Flag	false
Document Period End Date	Mar. 31, 2026
Document Fiscal Year Focus	2026
Document Fiscal Period Focus	Q1
Entity Registrant Name	PLUM ACQUISITION CORP. IV
Entity Central Index Key	0002030482
Entity File Number	001-42472
Entity Tax Identification Number	98-1795710
Entity Incorporation, State or Country Code	E9
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Shell Company	true
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Address, Address Line One	2021 Fillmore St. #2089
Entity Address, City or Town	San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94115
City Area Code	(929)
Local Phone Number	529-7125
Class A ordinary shares, $0.0001 par value per share
Document Information [Line Items]
Title of 12(b) Security	Class A ordinary shares, $0.0001 par value per share
Trading Symbol	PLMK
Security Exchange Name	NASDAQ
Warrants to purchase one share of Class A ordinary shares
Document Information [Line Items]
Title of 12(b) Security	Warrants to purchase one share of Class A ordinary shares
Trading Symbol	PLMKW
Security Exchange Name	NASDAQ
Units, each consisting of one share of Class A ordinary shares and one-half of one redeemable warrant
Document Information [Line Items]
Title of 12(b) Security	Units, each consisting of one share of Class A ordinary shares and one-half of one redeemable warrant
Trading Symbol	PLMKU
Security Exchange Name	NASDAQ
Class A Ordinary Shares
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		18,492,875
Class B Ordinary Shares
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		5,750,000