I was on my way to work and car started to run rough stumble and check engine light started to flash. Immediately turned around limped home about 3 miles. Changed plugs and swapped some old coils around. Still idles low and strong gas smell from exhaust. Any ideas need my car for work.

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    Welcome to the site. We need more information. Can you plug in a scan tool and see if there are any codes?
    – Zaid
    Nov 30, 2015 at 6:41
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    Also, after you get the codes, check the fuel pressure at the rail and tell us the reading. Nov 30, 2015 at 12:16
  • No i dont have a scan tool or fuel pressure gauge.I know the car is running lean.strong gas smell out the pipes.im getting at a minute of air releasing after i shut it off.sounds like passenger side up near radiator.4th and 5th gear it will bog and cough.any help.appreciated. Nov 30, 2015 at 17:15
  • Swapping coils and changing plugs will not make a quick fix. You need to plug in a scan tool and retrieve data. There are over 1000 reasons that check engine light can come on. Thats why diagnostics are important. If you take it to a parts store they will usually scan it for you.
    – cloudnyn3
    Nov 30, 2015 at 21:39
  • I dont know its a good idea to drive it.when i tested it from plug change it bogged worse as i went.a couple blocks.any ideas at all. Nov 30, 2015 at 23:14

2 Answers 2


I believe you have a bad Engine Coolant Temperature Sensor (ECT in Ford nomenclature). The code P0116,the smell of gas, and the rough idle are all symptoms of a bad ECT. Its Ford's part number F5AF-12A648-AA. Get the OEM part. Its about $25. Be careful replacing it because your car has a plastic intake manifold that tends to break.

  • I also changed the ect sensor the crank sensor the cam sensor and the egr.now i get po116 and the po304.could a dirty cold air intake filter cause the misfire in #4 and the 116 code which is misfire detected in first 1000 reolutions after start up. Jan 10, 2016 at 0:58
  • Is the car modified in any way?
    – race fever
    Jan 10, 2016 at 22:19
  • No big mods cold air and exhaust Jan 15, 2016 at 0:05

Based on the codes, I'd say race fever's spot on:

P0300 - Random/Multiple Cylinder Misfire Detected

P0116 - Engine Coolant Temperature (ECT) Circuit Range/Performance Problem

P0304 - Cylinder #4 Misfire Detected

P0174 - System Too Lean (Bank 2)


I believe what's happening is the coolant temperature sensor is giving no signal or a signal that's out of the normal range (P0116).

Under such circumstances, it wouldn't surprise me if the ECU assumes a default temperature which is an under-prediction when the temperature is warm (engine running rich, smell of fuel in the exhaust) and an over-prediction when the temperature is cold (resulting in the misfire codes).

The fix

I don't know if the ECT sensor is a common issue on this Mustang. Before you buy a new sensor, make sure that the sensor signal is getting picked up by the ECU using a scan tool.

If you obtain no signal or a constant temperature readout via a scan tool while the engine is warming up, this would indicate a loose connection or bad sensor.

Hope this helps.

  • ^ This is best answer. Mark it as the correct one when the time comes.
    – race fever
    Jan 1, 2016 at 20:29

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