rough idle

[satchel]

Picked up a new to me 2000 100 last night and it really drives well, but I noticed when it was warmed up and sitting in traffic that it got a really bad idle. The RPM bounces around 400 rpm from 500 - 900. Once I get up in speed it virtually disappears as far as I can tell. With as much as it is bouncing I really would have thought I would get a CEL, but nothing. Also it appears to happen with the A/C on or off.

Thoughts?

 

[Emcd]

mine had the same issue. my TB needed cleaning. it's an easy job. Check the FAQs for pictures if needed.

 

[satchel]

mine had the same issue. my TB needed cleaning. it's an easy job. Check the FAQs for pictures if needed.

Did yours do it only when it got warmed up? I understand the need for cleaning up the TB when there is a rough idle, but would have assumed it would be rough whether cold or hot. Don't get me wrong, I'll try to clean anyway, can't hurt.

 

[arcteryx]

you could also check for holes in the intake as well as clean/test your MAF. FSM shows how to do the latter.

 

[Emcd]

it was worse on colder days, but it wasn't great when hot either. i noticed a big flat spot in my throttle range was gone to. might be a coil failing to.

 

[arcteryx]

do you have any codes?

 

[satchel]

I meant when the truck was cold or warmed up. This seems to be happening only in closed loop operation (truck is warm and using sensors) for some reason. I thought maybe the coil as well but I think I would see something with that at higher speeds as well and from what others say, sounds like it should throw a CEL if that goes out. All sorts of things could cause a rough idle, from fuel injectors to coil and plugs, TB and so on, I'm just trying to think what makes sense to tackle first given that it is a closed loop error and only on idle with no CEL. I think TB/intake leaks is probably first bet once I get it back from the wifey.

 

[satchel]

do you have any codes?

nothing. That would be too easy, right? haha

 

[arcteryx]

coil packs are a problem but normally they are accompanied with a p0300-p0308. cleaning the TB is always good. but I would look at the MAF and intake to see if there is any unregulated air causing the rough idle. although it would be present when cold too. amazingly MAFs are very inexpensive on these compared to previous models. you can clean it with some maf cleaner and a toothbrush or something similar.

 

[satchel]

Yeah, now that i think about it, the MAF may be a good place to start as I don't believe that would cause a hesitation until the truck is warm. I'm not sure on this truck, but on most others, 02 sensors/MAF sensors are not used until the truck is warm and in closed loop, so that could for sure be the problem if this is the same.

 

[2001LC]

Many thread on "D" Vibration.
I found this took care of common cause.

1. Add a can of 44k to fresh tank of 91oct gas, drive to empty, then refill.
2. Test fuel pressure. Pinch return fuel line (Edited: Pinching could damage line!) is quickie test.
3. Test gas cap.
4. Disconnected battery for 30 minutes to reset ECU. THIS IS A MUST
5. Check Air filter.
6. Check PCV, lines and all vacuum lines.
7. Use a spray MAF cleaner.
8. Clean TB.
9. Clean, Grease & reconnect battery post.

 

[satchel]

Many thread on "D" Vibration.
I found this took care of common cause.

1. Add a can of 44k to fresh tank of 91oct gas, drive to empty, then refill.
2. Test fuel pressure. Pinch return fuel line is quickie test.
3. Test gas cap.
4. Disconnected battery for 30 minutes to reset ECU. THIS IS A MUST
5. Check Air filter.
6. Check PCV, lines and all vacuum lines.
7. Use a spray MAF cleaner.
8. Clean TB.
9. Clean, Grease & reconnect battery post.

That's great info, thank you. I'll do some searching for clarification on a few of those but that looks like a great list. Not sure how to test the gas cap myself and not sure what the greasing process is for a battery post, if you leave the grease on and what not, and where to pinch a return line and what to look for when pinching, but I'm sure it's all fully documented out here somewhere. Thanks again!

 

[2001LC]

That's great info, thank you. I'll do some searching for clarification on a few of those but that looks like a great list. Not sure how to test the gas cap myself and not sure what the greasing process is for a battery post, if you leave the grease on and what not, and where to pinch a return line and what to look for when pinching, but I'm sure it's all fully documented out here somewhere. Thanks again!

Most part store will pressure test gas cap for free. Quick test right after driving, remove gas cap, you should hear air rushing sound (more so on hot days.

NAPA has the 44K, great stuff.

Always good idea to clean battery post when disconnected. Post must always be greased or oxidation builds and will not charge properly. Oxidation on post will tax alternator, and sooner or later battery will die.

Fuel return line on my 2001 is connected to engine cover DS near fire wall. Pinch and fuel pressure will go up. If this helps, it may indicate fuel pressure issue. Do everything else first before this test as it is least likely the issue.

 

[arcteryx]

Many thread on "D" Vibration.
I found this took care of common cause.

1. Add a can of 44k to fresh tank of 91oct gas, drive to empty, then refill.
2. Test fuel pressure. Pinch return fuel line is quickie test.
3. Test gas cap.
4. Disconnected battery for 30 minutes to reset ECU. THIS IS A MUST
5. Check Air filter.
6. Check PCV, lines and all vacuum lines.
7. Use a spray MAF cleaner.
8. Clean TB.
9. Clean, Grease & reconnect battery post.

Don't forget to stand on 1 leg too.

Seriously, I don't see how some of those could be pertinent, specifically #3 and #9. Testing fuel pressure is not something easily done by the shadetree mechanic as specialized tools are needed, that's better left for a shop. If the gas cap were an issue, an emissions code would definitely be thrown.

 

[satchel]

Meh, any suggestion helps. If pinching the line for the return all the sudden makes the hesitation go away then I say it sounds easy enough to try, but yeah, anything more detailed on the pressure may be better suited for a shop.

 

[arcteryx]

understand and I didn't mean to come off as a smarta**, context can be missed in text. I just don't see how some of those would cause your symptoms. I am open to hearing how/why one thinks they are related to this issue. Ultimately, it's your time and budget though, so maximizing both would be ideal.

 

[2001LC]

If standing on one legs helps you, by all means.....

The above list has works for me every time to eliminate the "D" vibration. Basically I'm listing a minor tune up.
OP should baseline since it's new to him, oil & filter, fluids, lubes, plugs etc. may be way past service life we don't know.

Battery must be disconnected for thirty minutes to reset ECU, I found this key to stopping "D" vibration, if that is OP's issue. Greasing post is just best practice.

That said IMHO the "D" vibration is from multiple small issue adding up. Taxing the alternator draws on horse power, is just one more small issue. Turn on the cabin fan or headlights and you'll tax alternator, idle drops. Slightly weak gas cap may or may not throw code, buy worth checking. Se quickie fuel pressure test above, it's easy.

The above will get him started, before he moves on down the list to more expensive things like coils, injector, O2's etc....

 

[2001LC]

Meh, any suggestion helps. If pinching the line for the return all the sudden makes the hesitation go away then I say it sounds easy enough to try, but yeah, anything more detailed on the pressure may be better suited for a shop.

Bad gas can foul fuel filters, reducing pressure. 44K may help with this and cleans fuel intake system.

 

[2001LC]

Again start with 44k in at least half full tank of gas, drive off tank to get cleaning action.

I should have listed #2 fuel pressure test last.

 

[yeti in ga]

post back up if you figure out what it is...