Typical to an intake manifold gasket that is leaking, is an engine misfire, especially with the engine cold. In fact many cars will exhibit absolutely no misfires or idle speed roughness with the engine hot. Some may not even have lean condition trouble codes, in particular with speed density engines (no MAF sensor).

Engine Performance Diagnostics chapter 1 pages 914

Symptoms
check engine light (P0300, P0301)
misfire especially at low RPMs with the engine cold
customer replaced plugs, wires, ignition coil and fuel injectors in an attempt at fixing this problem

Fix
replace intake manifold gasket

Tests shown
how to perform a cylinder drop test (rpm drop test)
how to test for spark with a test light
how to use water to locate a vacuum leak

Tools used
scan tool
squirt bottle

Playlist
(Chapter 1) Misfire ID, Compression Tests, Vacuum Leaks, Fuel Trim, Head Gasket, Restricted Exhaust, Low Power, DMM
   • (Chapter 1) Misfire ID, Compression T...  

Related videos
Vacuum leak testing without a smoke machine (an SD Premium video)    • Vacuum leak testing without a smoke m...  
Ford F150 P0171 P0174 Trouble Codes vacuum leak (water test)    • Ford F150 P0171 P0174 Trouble Codes ...  
How to find a vacuum leak with water
   • How to find a vacuum leak with water  
P0506 IAC System RPM below expected (vacuum leak) Ford
   • P0506 IAC System RPM below expected (...  
Causes of lean condition trouble codes P0171, P0174 GM 5 3L
   • Causes of lean condition trouble code...  

For more information on this topic, I have written a “field manual” called Engine Performance Diagnostics which is available at www.scannerdanner.com as an eBook or paper book.
Want even more diagnostic training? Whether you are a DIY trying to fix your own car, someone looking to become an auto technician, or a current auto technician that wants to get more into diagnostics, subscribe to ScannerDanner Premium https://www.scannerdanner.com/joinsc... There is a 14 day free trial.
On ScannerDanner Premium I will bring you right into my classroom at Rosedale Technical College. You will find page for page lectures taken right from my book as well as exclusive classroom type case studies. What is so special about these classroom case studies? I pull live problem vehicles directly into my classroom and we troubleshoot them in real time, using and applying the theory and testing procedures we learn during the classroom lectures. There is no better online training of how to troubleshoot automotive electrical and electronics systems anywhere!

Disclaimer:
Due to factors beyond the control of ScannerDanner LLC, it cannot guarantee against unauthorized modifications of this information, or improper use of this information. ScannerDanner LLC assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. ScannerDanner LLC recommends safe practices when working with power tools, automotive lifts, lifting tools, jack stands, electrical equipment, blunt instruments, chemicals, lubricants, or any other tools or equipment seen or implied in this video. Due to factors beyond the control of ScannerDanner LLC, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Any injury, damage or loss that may result from improper use of these tools, equipment, or the information contained in this video is the sole responsibility of the user and not ScannerDanner LLC.