How to clean Fuel Injectors

If the blockage isn't bad (but bad enough that you notice it), an Italian tuneup works well on pre-GDI engines. This is when you drive the car at a high RPM with some variation and only shift it at near redline. You usually do this for ~10-15 minutes, sometimes longer as needed. The reason is that by driving the car fast, you're unblocking the injectors and cleaning the engine of any engine carbon deposits due to the car not being driven much (or very fast). The key thing to remember on a manual transmission car is DO NOT shift it until you're near redline - you want to hold it for a bit.

This works best if you can get it on a highway and legally do 70-80+, and ideally with new spark plugs before you do it. It doesn't work as well unless you can drive the car fast. The only other thing I may add before doing an Italian tuneup (especially if it's sat for a while) is to add fuel injector cleaner to the tank to get as much of it out as quickly as possible.

That said, before you go this route, check to make sure the carb adjustments are correct, as flooding out the engine with gas can make the problem worse. I'd also check the wiring and make sure the connection points aren't dirty, especially with the injector wiring and distributor cap if it's present.

If you do not want to go the Italian tuneup route, you can remove the injectors and take them to a shop for cleaning or buy a fuel injector cleaner, which will set you back ~$1k. You may or may not just want to have a shop clear the injectors and avoid paying for the machine needed.