Engine shaking during idle

P

POW

Member
May 23, 2014
38
Alright, so last couple days have noticed a solid shaking when I am either in Park or if I am in drive but stopped. It goes away, at least as far as I can notice, when driving. RPMs are fluctuating slightly, I see movement between 550-700 rpms.

The shaking isn't constant but almost like a slight burping every 2-4 seconds or so. Again, not a violent shake but noticeable to me sitting in the drivers seat.

I have 104,300 miles on it.

Here is everything that has been done on it recently:

  • New tires at 95K (last rotated at 100K)
  • New K&N Air Filter at 99K
  • Switched to synthetic oil (Mobil 1 w/ Mobil 1 oil filter) at 101.5K
  • New Water pump at 101,600
  • New Thermostat/CTS at 101,600
  • Coolant & Transmission flush at 101,600
  • New Serpentine belt at 101,600
  • New Radiator at 101,700
  • New Front Right wheel bearing at 103,400
  • Spark Plugs replaced 103,400
  • Throttle Body cleaned at 103,400

After the new wheel bearing, plugs, and cleaned the TB it ran like it was brand new. Took a road trip from Houston to San Antonio that weekend and had increased MPGs & it rode great. Last couple days I have noticed the shaking.

I had a family friend (mechanic for 20+ yrs) help me with the wheel bearing/plugs/TB. He didn't actually remove the TB, instead he just sprayed the TB cleaner into it and used his fingers/rag to clean it out without ever removing it. He said this way you don't have to mess with resetting the computer and all the problems that can come from that. Is this wrong?

Should I try resetting the system? Can I just pull the PCM fuses (10 & 28 right?) or do I need to disconnect the battery? Or should I not do this?

Only other maintenance items I need to do that I haven't is replace Transfer Case fluid & I guess front/rear diff, although aren't those supposed to be lifetime fluids?

Thanks in advance!
 
There's gunk on the back and on the edge of the disk that I don't think you can get without removing it. Which is why the How To article specifically says take it off, and reset the PCM by pulling the battery - which to remove the TB safely you should do anyway. Yes, pulling the PCM fuses is equivalent.

However, a clean throttle body usually helps an erratic idle that goes down excessively when the AC compressor cycles on. Yours may be something different. I'd pull the plugs for an inspection. Did you mess with the gap or touch the iridium tip when you installed them? Any chance a coil is slightly misinstalled and not clicked onto the plug nicely?
 
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Also noticed no transmission service interval listed (100k intervals). However, the fact that you keep good records like this in the first place is certainly a step in the right direction!

Yes, you will have to do as Roadie says and remove the throttle body. The front doesn't usually get too bad in relation to the back as long as your air filter is doing its job. The back gets caked with crap due to the design of the EGR, I believe. It is not recommended to push the blade with your finger to access the back half without removing it as this can cause extremely-expensive damage; it is best to remove it and use an appropriate cleaner.
 
Just to add on the TB cleaning, there should be 0 reason why the TB cannot be pushed by hand after the engine is shut off for awhile and key is removed. Do not attempt to push it if the key is to "Run" as it will be engaged at that time and you can snap the gears inside the TB that open and close the plate. As far as cleaning the TB and having to do a relearn, I honestly take my TB off 2 times a year to clean it all up and I do not pull the battery or any of the fuses for the PCM and I remove it, clean it and put it back on and go about my business and i'm fine. I clean mine so often that it never gets gunked up and it is never a problem for me to give it a quick scrub down and wipe it. As far as cleaning the TB if yours is really black and gummed up on the back side I suggest pulling the fuses for the PCM and do a relearn as yours is so dirty it can benefit from it. There is no problem doing a full relearn for it, just some people have complained about issues with a broken vent solenoid for their HVAC system but honestly I view those with that problem are going to run into it eventually with a busted gear in the box.

With your shaking, do you have the ability to have someone help you to pin it down? If you can get someone to help you have them sit in your truck and hold the brake down all the way and start up the truck and let it come down to idle speed. Open the hood and watch the engine and see how much it is shaking around. Have your friend hold the brake down all the way and shift the truck in and out of park and then switch it between drive and reverse and see how much the engine rocks. If it is shaking a lot side to side then you probably have bad engine mounts and need to replace them. If it does not rock a lot do you have your AC on while the shaking occurs? What if you put the truck into neutral and set the parking brake, does it still shake at idle?
 
Another addition to the things said about the TB, specifically calling out your mechanic friend.. The act of removing the TB isn't what makes you have to reset the pcm, it's the act of cleaning it because the pcm accommodates to it getting dirty over time then when you clean it, it's still tuned for the dirty TB and will run just as bad if not worse than it just being dirty. So, if he got it clean without removing it...it still needed to be reset.
 
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We generally advise removing power to the throttle body to remove it in order to more-easily access the back side, and as we're not dealing with a simple flap with a spring like in the days of the carburetor, it's still not suggested to push on it. The drive for the throttle body is designed to give the motor precise control over positioning, and plenty of leverage over the flap. Pushing the blade open could damage the drive unit to the throttle body, and it's a multi-hundred dollar part. A good throttle body cleaning solution will make the gunk "melt" off. Takes forever, and may take some GENTLE wiping with a lint-free towel to help it along, but it will come off.

The relearn process is to more-quickly adapt the PCM to the clean throttle. On a PCM reset, it's assumed the throttle body is clean, and if it is of course clean it takes just a few minutes for it to get adjusted. A PCM that hasn't done relearn rolling a clean throttle body will also adjust to it, but it takes considerably longer.

I'll cut Roadie off at the pass and say it now: if your HVAC actuator goes out from pulling the power, it was on the way out the door anyway. This is why pulling just the PCM fuses offers a workaround for this for the people who would like to push the problems to a later date.
 
All,

Sorry for my lack of replying.

I took the TB out yesterday and cleaned it real good. Pulled the 10 & 28 fuse while doing it. It seemed to help at first but overall still getting a slight shutter/shake. Someone else mentioned the motor mounts?

And, to clarify, I meant lifetime fluids for the diffs, not the TC. They are all on my to-do list here anyways.

Thanks for all your help & replies.
 
Yeah I would check the motor mounts. Easy to check if you have two people. It might be subtle breakage of the motor mount so make sure whoever is checking them looks closely. From the drivers side you should be able to tell excessive movement from the engine.
 
triz said:
Yeah I would check the motor mounts. Easy to check if you have two people. It might be subtle breakage of the motor mount so make sure whoever is checking them looks closely. From the drivers side you should be able to tell excessive movement from the engine.
Click to expand...
Any tutorials or write ups on how to check them? What to check for? How to replace? Parts, cost, etc...? To be honest, I don't have the first clue what to look for/do. Been searching around on here and the old site and can't seem to find anything concrete.

Thanks a lot!
 
So outside of this rough idle the car seems to run great but with the idle I am always just a little nervous that something is going to go wrong. This morning, sitting at a very busy intersection waiting for the light to change, i felt my car stall out & the dash blinked for no more than 1 second "Oil pressure low".

I gave a tap on the gas pedal and nothing, all the lights/radio & I believe air (although I didn't have much time to process as the light had changed and cars were already moving & honking at me). I put in park, turned the key off, removed it, stuck it back in and started it back up, the start took a second or two longer than normal but once i shifted into drive and drove (my office parking lot was less than 2 blocks away), it drove perfectly fine. Once I parked I started it a few different times and it started up no problem, checked the oil level which was fine as well.

Any ideas?

Starting to get a little tired of the constant one thing after another and just always being worried something is going to happen when I am driving it.

  • Any ideas on what happened above?
  • Any other leads on checking/replacing motor mounts?

Thanks a lot!

Edit to add:

I forgot to mention that ever since this rough idle has started it seems MPGs have dropped by a little. Nothing major. Maybe 1-1.5 mpgs but school also just started up which means traffic is worse in the mornings so a little more stop and go.
 
Motor mounts will cause a 10 Hz rotational vibration in the axis of the driveshaft (the thing to look for as vibration of the intake manifold especially), but will never cause the engine to stall out. That vibration never shows up on the tack or as dipping RPM that causes a stall. Your second throttle body cleaning process looked legit, but to prove it's not that, run around without the AC compressor on, and see if it happens again.

This issue might be unrelated, like a flaky ignition switch.
 
The_Roadie said:
Motor mounts will cause a 10 Hz rotational vibration in the axis of the driveshaft (the thing to look for as vibration of the intake manifold especially), but will never cause the engine to stall out. That vibration never shows up on the tack or as dipping RPM that causes a stall. Your second throttle body cleaning process looked legit, but to prove it's not that, run around without the AC compressor on, and see if it happens again.

This issue might be unrelated, like a flaky ignition switch.
Click to expand...
Thanks!

I will drive it around tonight and this weekend with no AC on and let y'all know how it goes. Being in Houston (crazy hot/humid right now) & having my 10 month old in the car with me a lot means I have windows up and AC on most the time.
 
POW said:
Any tutorials or write ups on how to check them? What to check for? How to replace? Parts, cost, etc...? To be honest, I don't have the first clue what to look for/do. Been searching around on here and the old site and can't seem to find anything concrete.

Thanks a lot!
Click to expand...

Any replies on this? Mainly location & how to's?
 
Look under "News & Support", "Article Submissions" and scroll down, you will find
at least one article on how to replace motor mounts.
 
So, car has been running great. That slight shaking is still there but up until recently was very unnoticeable. More recently, it got pretty bad and caused the check engine light to show up. P0304 code so saying my 4th cylinder. I am going to pull the spark plug and the ignition coil and see if anything is wrong.

Thinking ahead if I do need to replace the ignition coil can someone link me to the best one to order/buy? I haven't had much luck finding it and always hear about people having bad experiences with the off-brand ones.

If the coil/plug is bad, could this be causing my shaking and my rpms to bounce around slightly?

Thanks!
 
Don't mean to keep bothering but I can't seem to find a true OEM ignition coil anywhere online to order.. Anyone help me out with a link?
 
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