Clean Throttle Body now high/fluctuating idle?

[{tpc}]

So just got done cleaning the throttle body today. Everything seemed fine after I pulled the PCM fue for 15 minutes. Then when I went for the first drive I noticed the high idle. Attempted to find some stop and go, no luck, took it for a freeway drive and then some more stop and go, which was still hard to find. I noticed while in park, in would run up to 13-1400 rpms then go back down to 600-700 hundred then run back up...over and over.

I am concerned but I am assuming this is the pcm relearning the newly cleaned throttle body. Anything else I should look at? I also replaced the air cleaner while I was at it as well..

 

[The_Roadie]

Did you pull the battery as recommended? If not, which PCM fuse did you pull?

You really need (IME) a half hour of stop and go city traffic. Freeway and PARK aren't doing anything to help the PCM relearn the idle behavior.

 

[Blckshdw]

Did you happen to knock the IAT sensor out of the back of the intake tube? I did that once, had the same set of issues. Popped it back in, and all was right with the world.

 

[{tpc}]

Thanks for the quick reply, no no all tubes sensors and electrical connections are accounted for.

 

[gmcman]

Try this: Pull the NEG batt cable for about 15 minutes then reattach the cable. Turn the key to ON and let it sit there for about 5 min. During this time do not start the vehicle or touch the gas pedal, just turn the key on. After about 5 min, start the engine and don't touch the gas pedal, let the engine idle for about 10 min. Then go drive it.

At no time touch the gas pedal until you are ready to drive it.

 

[{tpc}]

Ok that sounds like a good idea, however don't I ris the HVAC actuator issue? Could the same thing be accomplished with the pcm fuses? Actually, I did that after I did the pcm fuses the first time, but I let the truck idle for about 20 minutes prior to the first drive.

 

[gmcman]

Could the same thing be accomplished with the pcm fuses?

I believe it's fuses 10 & 28. I agree...prob best to try that first.

 

[The_Roadie]

Everybody should know my attitude on the HVAC actuator issue. Better to kill one when you've got tools out and it's on your schedule. Rather than in the middle of a harsh winter or brutal summer when you REALLY need airflow of the desired temp. Weak actuators deserve to die!

View attachment 33850

 

[{tpc}]

Yes I get it, and am somewhat ok if they die, however, who knows what the remaining weather will be like, so i rather not break them now. I figure if resetting the pcm again doesn't do it, then I can go the full computer shutdown route. But if they die today I really don't have the time to fix them. I did check them today, since this is after my t-stat repair, and all work, so i guess I did something right lol!

 

[MAY03LT]

There's a vacuum line on the intake manifold of the XL/EXT's that some members have had pop off on them - it's the one between the resonator and the intake.

 

[{tpc}]

Ok checked that and still connected. Right now I have the pcm fuses pulled. Going to try 30 min and see how we go..

 

[{tpc}]

Ok so 2nd try on the fuse pull and a short amount of driving and it seems better so far. Not perfect, but better. FWIW, I followed GMCMAN's steps substituting the battery cable pull for the pcm fuses again for 30 min. My drive was short, but I went through the subs forcing my stop and go. Going to drive it for a bit more tonight in a little while in as much as the same way as possible. Thanks all for the help!!

 

[CaptainXL]

On the XL it's not uncommon for the rear HVAC vacuum hose to come loose or break midway which will create a vacuum leak. Vacuum leaks cause high idle. Block off all the vacuum ports and see if the high idle persists.

Also remove and inspect the throttle body gasket mounting surface and check to see if the gasket/o-ring is properly seated in the intake manifold opening where the throttle body is mounted. The gasket is blue in color.

Check fuel pressure regulator and it's hose for leakage as well.

 

[{tpc}]

After driving it last night, it has performed better, but it was still persisting. Its much less of a high idle now than it is a fluctuating idle. And the fluctuations were decreasing in their severity. So I am hoping that it is just the pcm relearning.

As for blocking off all the vacuum ports, I'm unsure of where to start. How many are there? Where would they be found? The truck didn't behave like this prior to cleaning, so I suppose its possible I broke something along the way.

As for the gasket thing, everything went back together fine, but I suppose it could have loosened up though I did use the torque wrench and torqued it to spec. I assume you are talking about the gasket directly behind the throttle body? If so, mine is orange (like the one in MAY03LT's video) not blue.

The behavior when it happens (and it has happened less since the 2nd fuse pull) is basically the rpms settle down slowly to right around 6-700 rpms then (if it is happening) they bump up to something like 1200 rpms and begin to settle slowly again. Its almost like the truck thinks it is about to stall out and then hits the gas. The interesting thing is, after both times I pulled the fuses, and I let the truck warm up for 10 minutes or so, it sat there at 6-700 rpms and idled just fine the entire time. The fluctuations didn't occur until during the first drive cycle.

 

[{tpc}]

Does anyone think this could be related to the idler pulley? (side note, is the idler pulley the one below the alternator pulley?) The reason I ask is because during a search for engine "whine" a post suggested the idler pulley going bad could be a cause a rpm fluctuation when turning the wheel. Now ours does it without turning the wheel but we also have a "whine" that varys with rpms.

When i had the belt loose I happened to spin this pulley a few times by hand (the one below the alternator). It spun around ok but it definitely felt "not right", by feel standards.

I swear the truck was not doing this prior to the tb cleaning, but my wife sent me a text saying she felt it drove fine, but it did fluctuate while in park, but she said it had been doing that before. It's here daily driver so I guess she would know better than me, but I usually notice these things. Anyways, I wonder if that is it?

 

[MAY03LT]

Does anyone think this could be related to the idler pulley? (side note, is the idler pulley the one below the alternator pulley?)

Yeah, the idler is the one under the alt. You can remove the belt and run the engine for a minute and see if the whine goes away. I don't think it's related, but the idler might have it's own issue since it didn't pass the "feel test".

I swear the truck was not doing this prior to the tb cleaning, but my wife sent me a text saying she felt it drove fine, but it did fluctuate while in park, but she said it had been doing that before. It's here daily driver so I guess she would know better than me, but I usually notice these things. Anyways, I wonder if that is it?

I encounter this all the time. I work on a vehicle, unaware of an unrelated preexisting condition, and on a road test the preexisting condition pops up.

How bad is the fluctuating? Also, when it's fluctuating while running in park, is the A/C compressor clutch engaging on and off?

 

[{tpc}]

Yeah, the idler is the one under the alt. You can remove the belt and run the engine for a minute and see if the whine goes away. I don't think it's related, but the idler might have it's own issue since it didn't pass the "feel test".



I encounter this all the time. I work on a vehicle, unaware of an unrelated preexisting condition, and on a road test the preexisting condition pops up.

How bad is the fluctuating? Also, when it's fluctuating while running in park, is the A/C compressor clutch engaging on and off?

Ok, gives me something to look at (idler). How in the heck do you get the belt past the fan and shroud? When I took it off the first time I kept looking at it like I have no idea how someone does this, lol.

As for the AC, good point. I will have to confirm this. I know last night it was on, because when I went to test out the HVAC doors I felt cold air and noticed it was set low, so I cranked it up to 70 because I wanted heat.

As for how bad, when it revs up to about 1200 rpm it sits there for a second, then slowly goes down about 100 rpm at a time. It gets to about 700 rpm and sits there a little bit longer (than at 1200), then it revs back up to 1200 and repeats the process. Its noticeable but not too much a bother. The only time its an issue is when you backing out of the garage or something and it revs (done it once on the way up the driveway as well), cause your in gear and not expecting the extra power.

 

[Texan]

Go up to Mayo's picture in #10. Notice the "shining" nozzle, it is on the intake
manifold. My SWB TB has a rubber cover on that nozzle. The LWB TB has a hose
for the rear HVAC on that nozzle.

 

[{tpc}]

Ok, so after returning home, and talking with my wife, she swears it doesn't behave any differently than before. So I checked the vacuum lines again, enjoyed a cigar, which allowed me to blow smoke into the area of side lines to see if anything was appearing to suck in, ie a leak. I didn't see anything of the sort. Then my next step was to play with the AC. I noticed that I could induce the symptoms by turning it on and off again.

So at this point I'm satisfied that it is ok. She isn't complaining about it and I am/was probably over concerned about it. But thank you all for giving me guidance and help with it, it DID help and is MUCH appreciated.

 

[IllogicTC]

If you want to get real fancy, get a smoke machine designed for testing for leaks. A cigar may not provide 100% diagnosis but I'm sure it was at least very enjoyable. If the A/C is causing this, my question is whether or not the clutch is properly engaging? The PCM adjusts the idle when the A/C compressor is on in order to maintain the same idle speed while having more power being sucked down. Perhaps a clutch which is not engaging properly would make the PCM think it needs to give the engine a little more juice, but there is no load on the system (thanks to the bad clutch) to bring it back to bear.

 

[{tpc}]

Well I don't know what to do now. My wife calls me this morning, now that she is paying attention to rpm, saying it never seems to idle below 1000 rpm. She says it is still driving fine, and I believe her, but I am also thinking she is being nice about it as well.

So I'm kinda in the middle now, between I don't give a crap about it, and I know it wasn't doing this prior to repairs/cleaning. I drove it for a week during the bitter cold, and I didn't notice anything like this at all. I'm pretty anal about stuff like this so I notice the little out of the norm things more often than I care to admit.

Again, I could induce the situation with a on/off of the ac/heat system. I literally turned it on, watched it happen, hit "off" watched it go away a bunch of times. Could it be a bad IAC sensor? I think this is the sensor to the right of the throttle body that has a connector plugged into it? I did remove this connector when I did the throttle body cleaning, so maybe I messed it up somehow? Or could it be something to do with the sensor to the left that is on the tube connecting to the air cleaner?

Lets roll this back to the start.

Truck throwing codes of P0105 and P0128, on occasion clearing themselves, but always coming up, even after I cleared them. (prob for 6 months or more)

Monitored truck via torque app, to see coolant temp never reaching above 160F.

Removed battery (used memory saver), alternator, belt, T-stat and Coolant sensor. Replaced coolant sensor and t-stat with new, put back together.

Started truck, ran fine, idled right at 6-700 rpm. Ran it till it warmed up to 195F idling. Shut it down and called it a night.

Next day, removed throttle body that was severely gunked up and cleaned. Also replaced air cleaner with new. Reinstalled, reconnected all hoses, connectors, etc. Reset pcm via fuses for 15 min. Started up. Ran fine, sounded great actually, idled at 6-700 rpms. Cleared all codes via torque app at this time.

First drive, noticed high idle backing out of driveway and while driving. Didn't do a ton of stop and go. Came home, replaced upper radiator hose that appeared weak, "burped" the radiator that seemed to maybe have a air bubble in it. Pulled PCM fuses for 30-45 minutes. Turned key to on for 5 minutes, then started truck and let it idle without touching gas for 10 minutes, took it out for a forced stop and go drive for about 15 minutes through local subs. High idle seemed lower, still fluctuating idle but better. Shut truck off for a couple hours.

Same night, turned key to on for 5 min. then started truck and let idle without touching gas for 10 minutes. Took for a more extended drive of over an hour. Started with as much stop and go ans I could find lights for. In the middle a little highway cruising. At the end, more stop and go as I could find lights for. Again, high idle seems to be disappearing, still fluctuating but still feels better.

Next day, wife says seems to be driving fine. When I get home I start it, see the fluctuation, but also see it go away when I turn off AC. Can induce it on/off with ac/heat on/off. Try to blow smoke in areas of throttle body and vacuum lines, can't see anything "sucking in". Make sure again that all hoses and connectors are attached, they are and that nothing looks broken, it doesn't. Shut it down and call it good.

Today, wife is paying attention to rpms saying it seems to not want to idle below 1k rpms. I have a feeling I know what she is talking about, and its this situation. Truck idles up to 1-1200 rpms, then slowly idles down to 6-700 rpm, waits maybe 10-20 seconds then back up to 1-1200 rpms and back down. My feeling is she never sees it going lower because not enough stop and go for her into work and she doesn't have enough sitting time before she has to hit the throttle to go.

Thats all I got. It has yet to throw the codes again since my repairs. In the past I could clear the codes via the torque app and they would come right back the next drive cycle. Its been through probably 4 or 5 drive cycles since the last pcm reset. I suppose it could just be great timing that the ac clutch might be going out right when I did the repairs. I assume to get the belt completely off you have to thread it past the fan and shroud somehow? How long would it be safe to drive it like that? I mean the symptoms don't seem to appear as often until its on the road, so just idling it in the driveway I don't know if it would make any difference taking the belt off.

Any suggestions? Or should we just drive the damn thing as normal until something else shows up or the symptoms get worse?

Edit: Both times when pulling the pcm fuses I pulled 10 and 28. I think one was a 20 amp (yellow) and the other a 15 amp (blue) or maybe it was 10 amp. Either way both were labeled pcm on the fuse box. I have yet to do a complete battery pull.

 

[Blckshdw]

Is it safe to assume she had the HVAC system running when this was happening, or was this happening when it was off as well? Did you tell her about that finding so she could check that when she's driving it?

 

[{tpc}]

She never runs it with the Hvac system off. I left it on last night, so I am sure it was on whilst happening this morning. I will ask her to turn it off for awhile on the way home tonight and report what she sees. Assuming that is, that she will turn it off.

I don't know if this is a consideration or not, but would the fuel mixture running rich have a tendency to cancel out the fluctuation from the ac compressor turning on/off (if that is truly what is causing it?)?

Its about all I can think of. I have not changed the upstream o2 sensor either, so maybe now that part of it is running properly other parts are not? I doubt this sensor has ever been changed.

 

[KNBlazer]

I would hook up a scan tool and check the oxygen sensor, I remember reading a while back about a faulty o2 sensor causing idle issues...not sure if it applies to our platform though.... either way, if you haven't replaced and it's past the recommended interval, might as well....

 

[{tpc}]

I would hook up a scan tool and check the oxygen sensor, I remember reading a while back about a faulty o2 sensor causing idle issues...not sure if it applies to our platform though.... either way, if you haven't replaced and it's past the recommended interval, might as well....

Can I do this via the torque pro app? I thought I saw something about o2 sensors in there but is there a recommended way to use it to check this?

Edit: I suppose I can buy the actual socket for this without having to make one? lol. I'm sure I will change it soon enough, even if checking it shows it ok.

 

[gmcman]

Did you perform the tb relearn with the ac compressor on? If so or if you are unsure then I would do it again.....with it off.
You also need to be absolutely certain the narrow edge of the butterfly on the tb is clean.

 

[Blckshdw]

Can I do this via the torque pro app? I thought I saw something about o2 sensors in there but is there a recommended way to use it to check this?

After you go closed loop, the Bank 1 sensor should switch between .1 and .8V fairly quickly, and the Bank 2 sensor should be steady for the most part.

**please disregard my AFR and Tranny Temp readings in this screen shot, sometimes Torque reads them properly, other times they stick with these numbers**

 

[{tpc}]

Did you perform the tb relearn with the ac compressor on? If so or if you are unsure then I would do it again.....with it off.
You also need to be absolutely certain the narrow edge of the butterfly on the tb is clean.

You know, I am not 100% certain on this (learning with the ac on). As for the narrow edge, I'm a little confused of where/what that is. Do you mean the actual butterfly itself or the rest of the tb around it? Or just the edge of it? I know I cleaned the whole butterfly edges and all, it was pretty gunked up, I ended up using a toothbrush on it.

After you go closed loop, the Bank 1 sensor should switch between .1 and .8V fairly quickly, and the Bank 2 sensor should be steady for the most part.

Thanks, I get it now! Now I just need to get to the vehicle!

 

[{tpc}]

Ok so I have good news to report! I think my wife is trying to drive me insane, lol. That said, driving the truck tonight, it drives and behaves exactly as expected. With or without the HVAC on. I also checked the behavior of the o2 sensors which also behave exactly as described.

Maybe it took a bit more driving to relearn or something, I do not know. But it seems fine now.

My new plan is to switch vehicles for a few days after I do something like this, so I know first hand what is happening and can see the changes.

 

[lint]

I dont know if this as been said but i think the HVAC runs with the defrosters so it could still come up with the heat on in the mornings and if you took the throttle body off , you could have an air leak at the o ring ,or throttle body gasket . just a thought

 

[{tpc}]

Lint I actually forced it on by setting it cold tonight. I could hear the compressor coming on and putting a load on the engine, but unlike what was happening before, it had little to no fluctuation this time. I tried while driving and while in park. So out of the woods on this one, however now, the transmission hates me it seems. (this is in another thread)