Occasional low/rough idle at stop lights

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Jan 10, 2010
rapid city, SD
I have a low, rough idle that comes very randomly while stopping in drive at stops. After reading through the forum I replaced the intake tube thinking this was it....but it is still there. It is very random and doesnt seem to follow any pattern. I did the HG recently, but didnt replace the plug wires or distributor cap as they seemed good. I did put in new plugs and had the injectors cleaned. I also did a minor cleaning of the throttle body. Any ideas? Thanks
Cracked intake pipe my two cents..
If you mean the rubber tube that runs from the MAF sensor/air cleaner to the throttle body, I replaced it with no change.
Check for hard-to-see cracks in the hoses going out of your valve cover. Squeeze 'em and see if you find any cracks, mine had some that only became visible when moved, and were contributing to a rough idle when I bought my LC. Basically any breach that lets unmetered air into your engine will cause problems.

Another time I had the idle dropping to a rough 400RPM or so at stop lights (after I replaced the aforementioned hoses). When I looked under the hood afterward, the oil dipstick was out slightly, maybe 1/2". I pushed it back in and haven't had the problem since. It's a trivial point, but check anyway
I have the same issue and all my hoses are new. I read somewhere that the wires that run right by the EGR valve could be grounding/shorting out because the heat has gotten to the wire insulation. I haven't tried to cut into that little nest of wires yet as it doesn't look too fun to cut into something that "looks" ok. Maybe eventually, I'll get sick of the low idle and do it as the weather gets nicer.
But I believe that would be the next area to look. Correct me if I'm wrong anyone.
i have also replaced those hoses. I did rewrap the harness where it goes by the egr valve as the old harness sheath had come apart. If it is the harness, would the rough idle happen randomly and how do I fix it.
Subscribed. I've got similar issues with mine. Rough idle happens in Drive as I stop the truck at a light. If i put it in neutral, it goes away. If I wait 10 seconds (give or take), it usually settles down and idles fine, although it can come and go if I wait long enough. As soon as I drive off, it's fine.

I'll have to check the intake tube, but all my vacuum hoses and other random "top side" hoses around the valve cover have been replaced. I've also done plugs, wires, dist cap and related maintenance.
I have the same issue. Néw plugs cap wire and rotor and cleaned the throttle body. Intake hose seems fine, can't find any cracks visually. I read somewhere to do the fuel sock, that's what I am planning next, as I am getting sick of this issue. I am unsure how that causes these symptoms but for 9$ why not.
I had the same problem. I checked my rubber intake hose for cracks and did not have any. My PVC valve hose had a crack where it connects to the PCV. I added a hose clamp till i order a new one. I also removed the IAC valve and cleaned the carbon on the tip of the plunger. One of these fixed my low idle roughness.

Also heres a tip. Replace the Phillip head screws with 5x.8-16mm Allen head screws. You only need to remove the plastic facia cover on the forward valve cover to install or remove the lower Allen screw. Its way easier then messing with the Phillips screw on the lower part.
It sounds similar to when I bought my truck and had it shipped to ABQ from Arkansas...For sh!ts and giggles, unhook the battery for 10 minutes or so then hook it back up, then go drive lots of start and stop traffic. The comp. might need to "relearn" it's elevation. Doesn't cost anything to try...
Ok thanks tomm project. I already did the cracked pcv hose, new pcv, and grommet.
Checked the intake hose can't see any cracks? Maybe I should just get a new one due to age. On the iac is there any adjustments to worry about or anything braking or just unscrew, clean and reinsert( set points or gaps) I already cleaned the throttle body, it was black and loaded.
I don't know about ya all, but I had a very similar issue. It ended up that the rubber seal going into the distributor was leaking small amounts of oil into the distributor. Had it changed out along with new cap & rotor. Fixed my problem. Maybe not your issue but something to look into??? Just an idea, I don't know, I have slept since then.

I had kind of postponed working on the problem as it was happening very randomly. Now it happens just about every time I drive it. I tried to pull the IAC but am having trouble getting the lower screw out. I am going to attack it this week. I am going to start with the IAC, then check the wiring harness. Would bad plug wires or a bad cap/rotor cause this?
Certainly possible, but in my case the plug wires, cap and rotor were all replaced in the last year and mine is still rough.
I did everything to resolve this. Plugs,cap, rotor wires, and still had the problem! I couldn't see any visible leaks in the intake tube, however after tapping the accordion part with electrical tape, my issue was solved! However I still have not replaced the hose and have no problems
The idle has went from occasionally rough at stop lights to barely running in drive or park about every time I drive it. It still runs fine above idle. I have replaced the intake tube, cleaned the IAC, checked for oil blowby in the distributer, and made sure the PCV system is working. I am going to order new plug wires, cap, and rotor although I have a feeling that wont solve it either. I put new insulation around the wiring harness when I did the head gasket. Im trying to get this figured out before the weekend as my clubs monthly trail ride is this weekend. Any other ideas? Thanks

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