Moving on to my next problem. My idle can some times fluctuate/oscillate between 600-1400rpm and cant exaxtly pin it down. It only occurs when the truck warms up and its worse when the truck is in drive. It idles much better in park, but sometimes it fluctuates a bit in park too. Its fine when actually driving as well. Very often, it will go days or even weeks without issue, then it starts up again. I replaced the egr control solenoid last year for a seperate problem, so that should be fine. Tested the ohms on my iac, thats fine. Tested various vacuum tubes, no leaks so far, although im definetely not ruling that out. My only clue so far is that when i unplug the vacuum tube from the egr valve, the problem does go away. But, ive tested the valve in a couple different ways, and it seems to be working correctly. Ive hooked up a vacuum pump to the valve and applied a vacuum it opens and closes as expected. I also sprayed some carb cleaner into the valve and saw no change in rpm, which indicates the valve isnt leaking. So, since removing the vacuum from the egr valve seems to stop the fluctuations, it seems like the vacuum level entering the valve is all wrong. Although, the vacuum is coming from the egr control solenoid, which should be working fine! Frustrating. Maybe the valve is bad, but im just not testing it correctly. Any thoughts appreciated!

 

No, the EGR valve is not bad. There should be no vacuum applied to the valve at idle to open the valve. You need to start investigating that. Begin at the control solenoid. See if its leaking or receiving signal to activate.

 

Thanks for that. I wasnt 100% sure that there should be no vacuum applied to the egr valve at idle. That helps narrow things down. There is no vacuum at idle when the engine is cold, only when things warm up a bit. So seems like something is telling the control solenoid to open up when it shouldnt. The control solenoid is relatively new, and its not allowing vacuum out at cold start, so i am really leaning towards it just being activated at the incorrect time. But, i will double check it again. Sounds like there are several variables the computer considers before opening the control solenoid. Not sure the best place to start on that. Throttle position sensor? Or maybe the evp sensor that sits on top the egr valve? Really hoping its not the pcm/ecm. Thanks again for the message.

 

 

Suggestions here -

Inspect the IAC for crud buildup, a known problem with this generation. Carb cleaner works well to clean out so that the piston moves freely.

Had challenges with the EGR system, went through the valve and position sensor, found the control valve had a foam filter on the bottom of it, apparently to bleed vacuum off by admitting fresh air. Filter was plugged solid, efforts to clean resulted in destruction of the valve, so replaced. All good-to-go after that. Since you state you've recently replaced, perhaps a bad-out-of-the-box unit?

 

Good video, thanks! I've verified the solenoid is working fine. I did notice that the wiring that connects to the egr valve sensor needs to be replaced. Just shaking it a bit causes the connection to be lost and the cel comes on. So, even if that's not the issue, it needs to be fixed anyway. I've tested the egr valve and that's working fine. While testing the vacuum coming from the solenoid, when in park, the vacuum can gradually pull 10hg of vacuum on my pump. When the engine revs, the vacuum acts as expected in some ways. The vacuum spikes, then drops to zero when I let go of the throttle. But then it either holds at around 5 hg, or builds up slowly to 10hg. Kind of head spinning. If i disconnect the wiring harness to the egr valve, the vacuum drops to zero and the egr solenoid will no longer open at all when i hit the throttle. I wonder if that indicates anything or is that normal behavior. I understand that the sensor is telling the computer the state of the valve, but I feel like the solenoid should still do its thing even if the wiring harness is disconnected. As usual, I'm probably wrong though.

 

Good idea with the iac. I checked the ohm rating on it, but didn't remove and inspect crud. I actually ended up just replacing the egr solenoid. I hate ***** nilly replacing things without at least being 95% sure it's the problem but ill live I suppose, and it seemed possible with how erratic the vacuum was acting. So far I haven't had any issues, but ill need more time driving since it can be intermittent. Thanks for the message! I'll update if something comes up.

 

Update: After cleaning iac, the idle has noticeably improved. It was pretty black in there. After getting on/off the freeway a few times, still no fluctuating idle and the tach holds real steady at stop lights. Thanks for the suggestion!! Hopefully this holds up.