Rough idle on Vortec 5.7

[HotWheelsBurban]

That's what I would think. My only experience with the IACV is with the Burb a few years ago. Replaced the TPS as it was bad( throttle fluctuating wildly even at idle) and was told that's what it was. Also was told that it and IACV usually fail around the same time. So replaced the IACV a week or so after the TPS; truck ran noticeably better, but the root cause of the problems was still Passlock.
Another nice thing about Rawhide being a 97(and a very early production 97 at that); he doesn't have Passlock!
As stated earlier, this truck has too many things about it that I like,and are things we need, for me to give up quickly on it. Similar to the Burb....

 

[Pinger]

That's what I would think. My only experience with the IACV is with the Burb a few years ago. Replaced the TPS as it was bad( throttle fluctuating wildly even at idle) and was told that's what it was. Also was told that it and IACV usually fail around the same time. So replaced the IACV a week or so after the TPS; truck ran noticeably better, but the root cause of the problems was still Passlock.

If I remember - I'll check my idle speed across drive, neutral and park when on gasoline tomorrow.

Another nice thing about Rawhide being a 97(and a very early production 97 at that); he doesn't have Passlock!

Stop scaring me with Passlock! My 'Burb still has it.

As stated earlier, this truck has too many things about it that I like,and are things we need, for me to give up quickly on it. Similar to the Burb....

You won't be giving up on it. I'm 5000 miles away and can see that! You'll iron the bugs out and the truck will be the better for it.

 

[HotWheelsBurban]

If I remember - I'll check my idle speed across drive, neutral and park when on gasoline tomorrow.



Stop scaring me with Passlock! My 'Burb still has it.



You won't be giving up on it. I'm 5000 miles away and can see that! You'll iron the bugs out and the truck will be the better for it.

Thanks very much for the vote of confidence!
I've been looking online for tool boxes and a camper shell.....too bad @Dravec took the thread title about "I may have an addiction". My brother kinda thinks I do! He enjoyed riding around in the AC yesterday and last Saturday though....

 

[454cid]

With the IAC, the passages in the throttle body need to be clear also. I recently cleaned up my throttle body, by removing it from the truck, removing the IAC and TPS, and cleaning it with carb cleaner, degreaser, and soap/water and a tooth brush. I think I also used electronics cleaner on the TPS.

I'm not saying this is necessarily the issue, but maybe.

Another idea, and this is really a guess.... you mention it's after you've been driving awhile. I wonder if the EGR could be sticking open slightly. Maybe pull it, and scrub it up with some oven cleaner.

 

[Dravec]

If you replace the IAC, make sure to only use an AC Delco or GM Genuine unit. Absolutely, positively, under no circumstances should you use an AutoZone or O'Reilly's unit. They are universal and require "fine tuning" that you'll never get right. The Delco just drops right in and works from the word GO. Went round and round with that problem on my old K3500 many years ago. 3 IAC valves from AZ, one from the leprechauns, and never could get it. Finally got p***** off, bought one from the local GM house that I can't stand, and wound up doing a hot swap in a truck stop parking lot in 110° July heat. Instant fix by using the Delco part. Lots of other things I've used Duralast, and never had an issue. This one part though, use Delco.

 

[HotrodZ06]

Just a possible but could the fuel pressure regulator be leaking raw fuel in the intake, enough to bog it down at 500 rpm but not enough to bog it at 800 rpm?

 

[Dravec]

Thanks very much for the vote of confidence!
I've been looking online for tool boxes and a camper shell.....too bad @Dravec took the thread title about "I may have an addiction". My brother kinda thinks I do! He enjoyed riding around in the AC yesterday and last Saturday though....

And to be fair. You have 2. I now have 4. Had 3 others in the past. And I can't help but continue to look for more. Because I have an addiction.

 

[HotWheelsBurban]

And to be fair. You have 2. I now have 4. Had 3 others in the past. And I can't help but continue to look for more. Because I have an addiction.

Counting the one we bought in '05, that got wrecked in '12( though parts of it live on, attached to the current Burb) this makes 3.....but you're still way ahead of me!
But I changed the fuel filter ( took longer to gather the tools from 2 vehicles and the box that stays at the shop, than it did to change the filter). And it runs a LOT better than it was ( though except for the occasional roughness,it was running okay). Driving back into town from the suburbs, it had better acceleration and the idle was very smooth. The only roughness at all, was slowing down to go into the HEB parking garage upper deck. It's kind of a steep grade, and you can't gun it to go up because there's parking spaces right at the top of the ramp. But even that was much less than it had been doing....
And the old filter was heavier than the new one. Since it's relatively easy to change, I might do it again once we get a few months down the road.

 

[Donald Mitchell]

Egr valve is easy to check.

 

[Pinger]

Just a possible but could the fuel pressure regulator be leaking raw fuel in the intake, enough to bog it down at 500 rpm but not enough to bog it at 800 rpm?

Or - very similarly re bog at 500 but not at 800 - FPR not closing as far as it needs to and/or restriction in return line causing higher injector pressure and richness that can't be compensated for by it being open loop or, O2 sensor issue.