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Q: After adding fuel additive, SUV performed badly

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After putting a complete fuel system cleaner additive into my gas tank, my SUV has been having bad performance. There is a rough idle, it hesitates when I accelerate, the muffler putters, and it has stiff brakes. I used the technique of running the gas tank until empty and then refilling it, but that did not solve the problem; it still exists. I am wondering if that means that it was not the additive I put in. Perhaps it is just coincidental that the problem started at the same time as adding the additive. Another thing that is happening since this started is that the check engine soon display on the dashboard is appearing. What is the cause of this problem and what can I do to fix it?

A: I would suggest checking the EGR valve (exh...

I would suggest checking the EGR valve (exhaust gas recycle). Inside your motor, temperatures can reach 2500 degrees. This is when the EGR valve is needed. When engine temperature is slightly cooler, such as when idling, the EGR valve function is not needed. EGR flow is not needed at idle, and in fact, can cause a rough idle. You may also want to test the distributor and spark plugs and wires. These can also cause rough idle and poor performance when they are old and need to be replaced. If you would like this checked, a certified professional from YourMechanic can come to your car's location to diagnose the rough idle and acceleration, and can replace your EGR valve if necessary.

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