I recently bought a 2004 sonoma with a 4.3 v6. I just recently put new plugs, wires, air filter, and oil. I am noticing that when the truck is warmed up to operating tempature it has a lope in the idle. The truck idles about 600-700 rpm. Then the motor will hesitate drop 50-100 rpms, as well as oil pressure. Then immediately returns to normal. It does this constantly while parked, and feels worse when the truck is in gear at a stop light. There seems to be no problem while accellerating or driving. The only thing I can think is that I had the air cover off the top of the carb and when I put it back on the circular seal is old and isn't sealing properly. Any body with the same problem give me a clue to where I should start looking to fix problem?
2004 gmc 4.3 v6 idle trouble
- Thread starter tad32287
- Start date
Molson02536
New member
DO you have your A/C on at the time?? The A/C clutch when it engages and dis engage will cause the engine to fluctuate like you have described. Try idling the engine with the A/C off and see if the idle stay's constant.
If the A/C clutch is cycling on and off, then you have a A/C issue and will need it to be checked out. If the engine's idle still fluctuates with the A/C off, then try cleaning your IAC ( Idle Air Control ) valve. This can be done by cleaning your throttle body and making sure you clean out the IAC passage way at the back of the throttle body opening bore.
Good luck and keep us posted.
I did pull the IAC out and cleaned the carbon off just after posting and it aided with the idling problem. I could still feel the hesitation but it was not nearly as bad. Now just a few days later its back to the way it was. I did not clean the bore out. It gives the idling trouble whether the AC is on or off. I was thinking it might be the fuel filter getting clogged and starving of fuel, so I tighten the idle screw to allow more fuel and it didn't help, it just made the stumble not as noticeable. I will pull the IAC back off and clean the bore this time too. I was wondering if the EGR could also be the culprit.
Molson02536
New member
Check your vacuum lines, common for the vacuum line on the drivers side of the engine to the vacuum canister to go dry and crack. Yes you can try cleaning the EGR valve and that will fix the issues if it is a bad EGR valve.
Try Giving your engine a http://www.seafoamsales.com/ treatment, your going to need two cans of the Seafoam to get the job done right is what i have found.
Good luck and keep us posted. http://gmcowners.com/gmc-forum/showthread.php?t=13770
It's been a few weeks since the last post, but I have checked all of the vacuum lines and found no problems. If were to be a vacuum line wouldn't it cause the engine to rev higher rather than studder and hesitate. The only two things I have left to do, before I start dumping big money, is to replace fuel filter and possibly the coil. I raised the idle on the truck which aided the hesitation but its still there. That in my eyes rules out a fuel issue. I was thinking that maybe the coil is going bad and at lower rpms it causes the engine to miss because of low voltage? Anyone with a similar problem find any fixes?
Molson02536
New member
There is not adjustment to the idle on the throttle body, the adjustment you have mentioned and adjusted is the adjustment to your throttle body blade to keep it flushed and seated properly on the throttle body bore. Adjusting that will cause you to have more issues then should have.
The IAC (Idle air control) valve regulates the idle if the engine and will cause issues if it's dirty with carbon build up, also a carbon up EGR valve will also cause this along with a bad vacuum line.
When you adjusted the throttle body blade, the TPS will indicate to the PCM that it's open and will not send the proper signals to the IAC since the PCM thinks your on your throttle. So any adjustment to the engine's Idle make from the PCM will not be made and your idle will be random on engine load, air temperature, ECT. The throttle blade should be closed 100% without any binding to your throttle body bore.
Try this to reset your IAC and PCM. Turn your ignition keys to the run position "engine not running" then pull the fuse out for your ECM, think there are two of them so pull them both and after 2 min reinstall the fuse. You should hear the fuel pump energize the fuel line.
Now to reset the IAC turn the ignition off for 1 min and then turn your ignition to the run position for 30 seconds then start the engine. The 30 seconds will reset the IAC, you engine may stall at first but don't touch anything and let it stall out.
Turn the ignition off again for 10 seconds and turn the ignition to the on position again for30 seconds and start the engine. Your engine should rev 1000+ and drop after a few seconds when the engine reaches operation temperature, then go for a test drive for your PCM to relearn your engine and transmission sensors. So you may find your transmission to shift firmer at first but then the PCM will compensate for it and bring it back to factory condition.
Good luck and keep us posted and back the throttle blade adjustment back to where is should be.