There could be any number of issues, including dirty air filter, throttle body, or intake valves, clogged fuel injectors, or even a vacuum leak. The easiest place to start is with the air filter. If it looks particularly dirty or if you cannot see daylight through the filter material, then it needs to be replaced. While you have the air filter off, check the throttle body. If it looks dirty, then it’s impeding air flow and needs to be cleaned. Our best product for this is B-12 Chemtool Air-Intake Cleaner (part #2209). After you get the air cleaner back on, then check for vacuum leaks. When the car is running, do you hear any kind of sucking noise from anywhere in the engine compartment? If so, find the source and correct the problem. If your vehicle is older, then it’s probably a good time to check anyway since PVC piping can become brittle and crack and old rubber tubing can get gummy from oil vapor and deteriorate. If those items are in order and the problem still hasn’t gone away, then you might have dirty intake valves and/or clogged fuel injectors. (If your car is old enough to have a carburetor, the treatment is the same as it is for fuel injectors.) Or, if you haven’t done any fuel system maintenance in the last year, then it’s definitely time for a quality fuel additive. At this point, you have a few options. The least expensive route to address such issues is to use a bottle of Super Concentrated Valve & Injector Cleaner (part #3012), while our strongest fuel additive is B-12 Chemtool Total Fuel System Clean-Up (part #2616). Either of those products will clean the intake valves and fuel injectors (or carburetor), but the 2616 will also clean the combustion chambers for the most thorough clean available from a fuel additive. If you haven’t used a fuel additive in at least 10-15,000 miles, be good to your car—go ahead and buy a can of the 2616. Good luck and let us know how it goes!