Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
Car was running great all day until I pulled up to a stop light and it started running rough with the check engine light flashing. After a short time 10 or so seconds it started running normal again and drove home with no issues. In the morning I drove to a shop with no issues. There was a code for cylinder 2 and cylinder 3 misfire as well as a map sensor out of race code. The shop replaced the coils and plugs. Car ran fine during test drive and during my drive home. Pulled into my driveway and car started misfiring again. I pulled codes and again cylinder 2 and 3 plus random cylinder and map sensor out of range code. I turned off the car and started it again and it ran fine. Hooked up the scanner and looked at fuel trims bank 2 trims were -8 and bank 1 were +8 at idle and zero when cruising. Issue is only at idle and intermittent. Any ideas where I should be looking?
Its really strange the shop would replace cylinder 2 and cylinder 3 ignition coils and plugs without properly identifying the problem.
From what I know about your car cylinder 2 and cylinder 3 are neighbors on the block but not in the firing order so I think only one is misfiring and the other ghosting relative to the location of the knock sensor(s). The misfire counters should have one at a much high count than the other.
To understand the problem this is really a two man job. One must operate the data acquisition system and the other drive the vehicle. It is the classic case of instrumenting a vehicle with a Pico scope and then trying to recreate the problem on the road. This on road testing is the reason the Pico Scope was designed. The only thing between the scope and the notebook is a USB cable. The scope can be located closer to the inputs, and with its deep memory you can have a high sample rate so as to not miss any meaningful events.
One man drives and the other observes and captures data. Most Automotive Pico scopes have 4 channels so you would monitor 4 things to narrow down the cause. In fact you would want to do this first before changing any parts as to not unduly influence root cause.
The blinking MIL light is of high importance meaning if it persists a cat could be damaged.
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