Q: Car won't accelerate & rattles

Hi There, What you are describing sounds like you may have a clogged catalytic converter. The catalytic converter converts toxic exhaust gases into less harmful pollutants that are suitable to be expelled into the atmosphere. When the catalytic converter is clogged, this causes these gases to be backed up into the exhaust system not allowing the engine to breathe properly. When this happens, the engine is forced to work much harder to expel these gases. This often results in the engine bogging down, hesitating, shaking and causing very poor fuel economy. This should also cause a check engine light to come on as the O2 sensors should be reading the incorrect amounts of oxygen in the exhaust gases if this is your problem. There are a number of reasons that may cause the catalytic converter to fail. They include: O2 sensor, fuel injectors, spark plugs, EGR valve system, exhausts manifolds, vacuum hoses, and MAF sensors. I would suggest having all of these components checked to be sure they are operating correctly. Generally, when the motor is continuously running too rich (too much fuel), this will ultimately destroy the internal components to the catalytic converter by way of igniting raw fuel inside the catalytic converter. Despite the catalytic converter’s ability to withstand very high temperatures, excessively rich fuel conditions can produce enough heat to push the converter material beyond it’s limits. These types of rich fuel conditions result in higher than normal temperatures that can cause matting erosion and burn away or melt converter coatings. If temperatures are high enough, the ceramic substrate itself will melt and clog. I would suggest having an expert from YourMechanic come to our location to inspect these components on your vehicle to narrow down what may have caused this.