weegie81

I have an 02 Trailblazer and here lately i have being running into the problem of when i start the engine it revs up then rev way low. the Rpm shoots up then falls way low but then stablizies out. It Does it when im idiling, i have to start driving for it to stop and level out otherwise it acts as if it wants to go dead. Then when i give it the fist inital bit of gas it almost dies. Im wondering if it isnt the fuel sensor going bad in it or maybe the plugs and wires need to be changed. Thanks for any help you may can provide me with. BJ

Nomad76lj

along with the plugs and wires i would try changing out the feul filter as well.

HARVICKFAN2933

About the trailblazer,
irst of all how many miles do you have on the truck, it sounds as if it is a fuel related problem and or a problem w/ the
electronic cooling fans, that is a commong problem. Let me know about the miles so I can provide you w/ proper info -- Jeremy

NCHEVYHEVN

That's not the proper way to fix a vehicle. I've been to many many forums and every single time some one says something about their idle being off someone fires off change the plugs, wires, cap, fuel filter and see what that does. They say this without knowing how many miles are on the vehicle etc. I guess that was the thing to do back when motors ran crappy or it's just an uneducated guess at trying to fix a problem but it certainly isn't the way you diagnose and engine problem on newer vehicles.

First off, how many miles are on it? What services have you had done to it? You run it low on gas often? Does it do it after it's warmed up or just when cold? How about the check engine light. Does it ever come on or stay on?

It's not going to be the fuel sensor as all that does is let's you know as the driver how much gas is in the tank. It doesn't have anything to do with the idle of the engine.

kcb37

I would agree with NCHEVYHEVN on not changing the plugs yet. However I will not be as rude and will explain why.
Other than idle it runs fine and it will smooth out at idle as I understand. The plugs being bad shouldn't speed up the engine at all past a normal idle. I would go with checking the Throttle Positoning Sensor. It almost has to be a sensor. Giving and starving air or fuel, to make it rev and die back down. If your light is or has been on, take it to Auto-Zone or Advance Auto Parts. They should check it for free. If your light is not on but has been and you have not disconnected the power it will still show a code when checked, so if they tell you your light needs to be on tell them to indulge you. Then you can laugh cause you knew something the parts store guy didn't. (gotta have some fun)

StotheP

I most likely know what your problem is. There is a commonly unknown part that costs about $120 called an "idle air motor". This motor has a rubber stopper that goes in and out to control air flow for the engine to run at the target 525 rpm's at idle. It only has 1 plug and 2 screws and it is right at the top front of the motor. You take off that top cover and then remove the 2 screws, the plug and replace it. There ya go =)

ZX1100F1

The Idle Air Control Valve (IAC) motor could be the cause but before I spent the money to replace this part I would have the dealer reprogram the ECM with the latest calibration.

Reason being: When you start the vehicle the ECM performs an EVAP diagnostic test as it opens the purge valve for a few seconds and then closes it to verify proper emission sensor operation. If the purge canister is saturated, the EVAP system on-board diagnostic test may cause the vehicle to correct for a rich condition from the canister. The vehicle would then become lean when the purge valve closes at the completion of the test.

The newest software calibrations fix this issue and is a great place to start.