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2002 Chevrolet TrailBlazer:
Idle Rough, Service Engine Soon

Alex Steele
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I have a 2002 Chevy Trailblazer that's idling rough. The service engine soon light came on and I had it checked at a repair shop. They told me it was bad gas so I added a fuel treatment. It's been about two weeks and it still has the same problem.




Without knowing the diagnostic trouble code(s) which triggered the service engine soon indicator, and exactly why the technician determined there was bad gas involved, I can take your question only so far.


But let's review the basics. If the fuel is visibly contaminated with water, dirt, sugar or what-have-you, a fuel treatment isn't gonna help. The fuel tank has to be removed and thoroughly cleaned, the fuel lines, injector rail, regulator etc. must be flushed out and the fuel filter replaced. Then you can fill it up with fresh gas, start the engine, and determine the condition of the fuel injectors. Other contaminants aren't so easy to detect but can damage the fuel system over time, such as excessive alcohol content (above 10% ethanol).


On the other hand, the trouble codes and performance of the engine may have indicated obstructed fuel injectors as the cause, and the technician simply assumed fuel contamination as the reason behind it all. If that was the case, and the fuel is visibly clear, there is a device to test alcohol content which you probably won't find outside of a dealership service department. If alcohol content is above 10% you can drain the tank and add new fuel to decrease the alcohol-to-gasoline ratio -- find your self a new gas station -- and then the fuel injectors can be accurately tested for obstruction with the appropriate equipment.


If the injectors are determined to be obstructed they can be cleaned with special injector cleaning tools (not fix-it in a bottle). If the cleaning procedure doesn't clear the obstruction, the injectors will have to be replaced. If there is severe contamination from foreign matter you're sometimes better off simply replacing all the injectors right off the bat.

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27 Apr 2018, 13:42
Eninge misfires...
OK you've cleaned the thottle body, changed plugs & coil packs & crankshaft solenoids, (etc.) and still have misfire...
Often overlooked, check the air resonator (plastic tank above valve cover). There is a crankcase ventilation hose from the valve cover into the air resonator. Check for the tube connector on the air resonator for leaks. Also check throttle body hose clamps are tight. If ther are input air leaks the engine management system adjusts the fuel mixture to attempt to keep engine power. The result over time can be carbon build-up in the cylinders which also can impact catalytic converter performance, O2 sensers and could cause exhaust valve burn.
28 Sep 2017, 00:00
The mechanic Is waiting for the problem to happen which is good. It appears he is trying to fix the problem rather then just make a quick buck. Your mechanic is using a scanner to detect the problem. Sometimes it can take awhile for the problem to appear again. Util the problem happens again you will just have to wait for the results.
27 Sep 2017, 17:11
Mine is in the shop right now for the same issue. The code indicated the cam actuator sensor or the actuator itself. The mechanic, of course, cannot get it to do what it's been doing every day for a few weeks. Running rough, check engine light flashing occasionally, acting like it has something clogging the fuel lines or filter.

07 Nov 2015, 14:00

Did you confirm spark at #6 after replacing the coils? What did the original #6 spark plug look like; wet, dry, or caked with oil (carbon)?
29 Oct 2015, 18:10
I've replaced all 6 coils and plugs on my trailblazer
And it still codes misfire on #6 what else could it be
19 Jan 2011, 19:48
You can stop by an auto parts store such as AutoZone and ask them to check the system for trouble codes.

This may give you a basic idea of the problem. But replacing the suspect part is not always a fix, and it can get much more involved. That's when you need a professional.
18 Jan 2011, 19:01
I have 2002 Chevy Trailblazer and service engine soon light came on and I don't want to take it to the dealer, cost to much money. If you can help us fix it ourselves it would mean a lot to us. Can you please help us?


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