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Q: Flashing CEL

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When i start my Audia4 up the engine is rough and the car is shaking and the CEL flashes. I took it to auto zone and have the following codes. p0304, p0171, p0301,p0300. Ive been driving my moms car because i don't want to drive the audi and the audi is also leaking oil. Before all of this happened i took my car to the mechanic because my CEL was on and they charged me 600 for a new fuel injector. but now present today my CEL is flashing . i went to Oreillys to get new coils and i changed all 4 of them but it still flashes and the car is rough so I'm not sure what to do . i don't have much money for a mechanic or the dealership. and i can't trust anyone expect for the dealership but thats going to be really expensive.

My car has 128000 miles.
My car has an automatic transmission.

A: The codes you recorded, P0304, P0171, P0301...

The codes you recorded, P0304, P0171, P0301, P0300, all pertain to engine misfiring. The flashing of the Check Engine Light signifies that the misfiring is "active" (ongoing) and consequently you should try to get the car repaired before operating it further and possibly damage the catalytic converter.

Ignition coils have to be tested before they are condemned. If you did not test them, it may be that the old one were perfectly good. It is best not to replace any parts until you either pinpoint the exact fault or work with a professional to get that diagnosis. Lots of times, perfectly good parts are replaced, without testing the parts, and that is needless nowadays with the availability of not only detailed Factory Service Manuals but mobile certified technicians such as those dispatched by YourMechanic.

Here is a list of the possible faults that a mechanic would check with the codes that you have:

If you seek a diagnostic, the technician from YourMechanic will walk you through a sequence and following is a partial list of some of the items that are relevant to the codes you recorded. Note, again, that any part that is identified has to be SEPARATELY diagnosed. That is, it is never wise to replace a part just because it is on a list of possibilities associated with a code.

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