Low idle/stalling new thread

[Trstrugar]

My truck is a 1994 GMC z71 1500 with a 5.7l and 700r4 tran. I am having low idle problems. The truck runs great when it's cold and first started up, voltage is at 14 and it idles normal. when in drive it will idle low, around 200. It gets worse after driving for about 20 minutes and it is fully warmed up. Voltage will be a little erratic, around 12/12.5. Idle will surge a little bit and when stopped and in drive will struggle to not stall, will stay around 100 Rpms. Also the check engine light will come on after it's been running a while. The only code I have been able to pull is a 44 o2 sensor. Plugs and wires look good, coolant temp sensor looks new, along with IAC valve, map sensor, and wiring to both. EGR looks pretty old so I haven't entirely ruled this out. I know I had a thread about this before but I never figured it out and the thread was pretty old. Any help is appreciated thank you!

 

[Trstrugar]

Also I had a mechanic mess with it for a couple weeks, and he told me his money was on the computer needing replaced, but he couldn't verify it without sending it in

 

[ram1220]

I had similar problems with my 90 Sierra 5.7l a few years ago. Idling issues as well as the CEL coming on at highway speeds. I changed the O2 sensor as well as the EGR valve and it cleared the issues right up. Since you are getting an O2 code I would start right there.

 

[Trstrugar]

I will give replacing those a try. Do you have any tricks for getting that one bolt off of the EGR in that inconvenient place?

 

[ram1220]

No sorry I don't. It's been a few years since I have changed the EGR. I can't recall what I did.

 

[Nathaniel2g]

I would change your o2 sensor before you touch your egr.

 

[sntrym]

Start with the O2 sensor. If you need to take EGR off, remove the air cleaner and the TBI, and the nut is easier to get to. If you feel adventurous, you can get to that nut using an open-end wrench without removing the TBI.

 

[Trstrugar]

I am going to take care of both of those things tomorrow and I'll let you all know how it goes. Can a bad EGR cause low idle? It's not intermittent it's constant. If I manually adjust the idle will it mess up my timing? Another theory I had was a bad ground somewhere if any of you have had experience with that.

 

[Jrgunn5150]

Also I had a mechanic mess with it for a couple weeks, and he told me his money was on the computer needing replaced, but he couldn't verify it without sending it in

Never see that "mechanic" again. ECU's almost never go bad. I've dunked them, burned them, they always work still. And when they do go bad, they just don't work anymore.

You can check the EGR by simply plugging the line to it.

Have you every cleaned your TB? How about the IAC passage?

 

[Trstrugar]

The IAC valve is new and the throttle body looked clean when I shined a light down it