03 trailblazer 4.2L idle drops below 500 intermitantly.


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my 03 tb is having idle problems. when a load is applied to the motor instead of idle ramping up it goes down. it doesnt die but does dip below 500. it will ramp up then go down if i sit there and just idle. if you watch rpm at idle it drops a couple hundred then jumps back to normal ive did the throttle body clean and relearn procedure. 160,000 miles. recent plugs and variable valve timing actuator. im leaning toward new throttle body. what do u think nation?
That sounds normal to me. If you turn the wheel at a stop or load down the alternator at idle, it isn't spinning fast enough to handle that heavy load and as a result it bogs down the engine.


Rarely does a throttle body need to be replaced. This actually sounds more like a miss.

Do you have an Android phone? Get a Bluetooth code reader (about $23 on Amazon) and the Torque Pro app ($5) from the Google Play store. It'll help you read the codes that might not be lighting up your CEL.


Clean ur throttle body I read it in a post once here and I did two weeks ago stop it on my 02 envoy. And I changing the fuel filter to give it better gas mileage


If you clean the throttle body, make sure you reset the pcm.


I have another thought on this. Upstream O2 sensor.

I have had a CEL off and on with my Sierra the past couple of months. Truck runs fine but always had a slight roughness to it at idle, and the RPMs would drop to 500 momentarily then back up to 600. I did plugs and wires a month ago and it improved dramatically, but still the occasional CEL and slight roughness at idle. I thought it was just something I had to live with. I finally checked the code and it was 1133, upstream O2 on the driver side. I replaced it this past Saturday. WOW what a difference! If not for my glass pack and looking at the tach, I would not even know it's running. I really had no idea an O2 sensor could cause a rough idle. I'm going to change my right side upstream next month, just because.

Fortunately your I6 only has 2 O2 sensors.

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