"Shudder" at idle

[mcc]

When idling at operating temperature, my engine intermittently shudders for less than a second with an interval of maybe 10 - 30 seconds. Torque tells me that the RPM drops to ~560 during the shudder then shoots back up to ~630 before instantly leveling back to ~600. The LTFT is about -9 to -11 at idle but gets to -2 to -5 when driving.

The horrible yellow dipstick was consistently in a quantum superstate of "full" and "low", showing a thick oil coating at both markings but nothing between them. I interpreted this to be "low" and added until the two middle dots were covered. This didn't solve the issue.

Is this anything I should worry about or should I just leave it alone? I'd prefer to not throw parts at it unless it's a sign of bigger problems.

Thanks!

 

[signalnc]

have you cleaned you throttle body? and did a throttle body relearn after cleaning?

 

[mcc]

It was thoroughly cleaned about 5.5k miles ago. It wasn't too dirty either.

Edit: And yes, I did a relearn after the cleaning.

 

[signalnc]

how many miles are on it and what other maintenance has been done?

 

[mcc]

It has ~109k miles on it. Some recent maintenance includes:

• [Summer 2011] Battery, belt
• [102.5k] Oil change @ local shop w/ Chevron 5W-30, 2x techron treatments, transmission flush + filter, transfer case fluid, ACDelco 41-103 plugs
• [103.5k] Cleaned throttle body
• [104k] Coolant flush, new radiator cap, thermostat (ACDelco), coolant temp sensor (ACDelco), hoses, clamps, fuel filter, air filter, upstream O2 sensor (ACDelco)
• [105k] Ignition switch (ACDelco), tire winch, CPAS replacement (GM)
• [105.5k] Oil change w/ Pennzoil Ultra 5W-30 + Fram XG3675 filter, front + rear diff fluid (Valvoline synthetic)
• [106k] Replaced power steering fluid w/ turkey baster method (ACDelco)
• [108.5k] New set of Firestone Destination LE2 tires

 

[signalnc]

maybe someone else will chime in. I cannot think of anything to help. Just being honest... the only thing I can think of is to re-do the throttle body relearn. it may help. I have also heard of getting a pcm tune, but I have no experience with it.

 

[CaptainXL]

Assuming you had none of those symptoms before all of this work was done...then I would retrace my steps and check it all again.

Specifically focus on the coils, boots, spring tension and spark plugs. Then disconnect the battery for 30 minutes and start the truck in park. Don't press the brake or gas pedal and let it idle like this for 10 minutes.

Also, it would help to have the STFT readings instead of the LTFT.

negative fuel trims mean you are running rich as fuel is being subtracted. Not indicative of a vacuum leak. Have you checked the fuel pressure regulator or for stuck injectors?

Also check your misfire data.

 

[dave_stumph]

I also had the same symptoms as described. No codes thrown but ended up being an intermittent misfire.
Bought a new coil pack and went through the cylinders. Ended up being #4.
All is good

 

[mcc]

Thanks for all of the suggestions so far! It's finals week so I have limited time to troubleshoot for now. I just walked out to the lot and let my Envoy warm up while watching Torque.

• STFT: Usually in the -4 to +4% range. Extremes were -10% and +9% (but very rare)
• No current or recorded misfires on all 6 cylinders, even during the "shudder". Can this figure be trusted?

The issue started a few weeks to a month ago. I rarely drive it when school is in session- I take the bus to campus. Most of the services listed were done last spring/summer.

I had my tires replaced 2 months ago (108.5k). I initially had them rotated but the two that were previously in the rear had flat spots. This led me to pay close attention to any vibrations, even at idle, because I wanted to be sure of the obvious.

I'll try disconnecting the battery and doing the relearn as well as visually inspect the coils, boots, etc. when I have time.

I haven't checked the fuel pressure regulator or the injectors nor do I have the equipment to do either. If I can't resolve this through simple means I'll probably have to take it in.

Dave, were you able to see live misfire data? Did it record anything for your problem?

 

[gmcman]

Did you use any dielectric grease when replacing the plugs on the tips? It's something I firmly believe in and is recommended.

Coil #4 is under the drip opening under the hood and tends to get wet. I would pull #4 and check the condition of the spring coil and also check for moisture.

 

[mcc]

The plugs were done by a mechanic. I don't know if they used dielectric grease or not.

I added foam under the rubber hood seal last year in an attempt to avoid the drip problem. Nonetheless, I'll take a careful look at it as you describe when I have the time.

 

[CaptainXL]

I haven't checked the fuel pressure nor do I have the equipment. If I can't resolve this through simple means I'll probably have to take it in.

?? I got a cheap fuel pressure gauge along with other simple diagnostic tools from Harbor Freight long before I ever got Torque and a $700 smart phone.

View attachment 27970

 

[mcc]

?? I got a cheap fuel pressure gauge along with other simple diagnostic tools from Harbor Freight long before I ever got Torque and a $300 smart phone.

Car: Driven rarely. I have some diagnostic tools but buying every possible thing I can get my hands on for every possible situation adds up to $$$.
Smartphone: Used to answer time-critical emails that directly effect my education. People routinely send me emails that they want answered within 1-2 hours. Sometimes I get them when I'm not anywhere near a computer. Torque + OBDII adapter = $20 and is usable for a plethora of diagnostics.

I'd say I have my priorities in the right place.

 

[CaptainXL]

Car: Driven rarely. I have some diagnostic tools but buying every possible thing I can get my hands on for every possible situation adds up to $$$


Smartphone: Used to answer time-critical emails that directly effect my education. People routinely send me emails that they want answered within 1-2 hours. Sometimes I get them when I'm not anywhere near a computer. Torque + OBDII adapter = $20 and is usable for a plethora of diagnostics.

I'd say I have my priorities in the right place.

I was just joking with the picture. But seriously, if you depend on a vehicle to get to school. Then?? What?? Pay a mechanic and pay big bucks or save money and do it yourself with tools you buy yourself? It's cheaper to buy the tools yourself. A fuel pressure gauge is $30. Not $$$. A diagnosis for fuel pressure problems at a shop however would be $$$.

You came to the forum asking for advice and I don't know your level of mechanical aptitude. You could enlighten us a bit if you want. I am guessing that since you know what fuel trim is then you are aptly mechanically inclined.

 

[mcc]

Unfortunately, It's going to be a little while before I can take a good look. My apartment lease forbids me from working on my car so it's not as easy as just finding some time to pop the hood. I'd rather not be fined.

Maybe I can drive it somewhere more friendly next weekend- until then, it's no worse than it was when I originally posted and it doesn't seem to be a pressing issue.

 

[jbacklund]

I also had the same symptoms as described. No codes thrown but ended up being an intermittent misfire.
Bought a new coil pack and went through the cylinders. Ended up being #4.
All is good

Did you have the negative fuel trims as well?

Would a intermittent misfire throw the fuel trims off track?

+1 on checking the plugs and coils.

 

[Mulehauler]

Recently had the same problem. I bought a new coil pack, changed cam position sensor and cleaned throttle body. Drove it about 25 miles on highway, exited and stopped to the sweet sound of a smooth idle.

 

[xx_gearhead_xx]

+1 on the idle, recently cleaned a dirty CPAS after getting a code and thought that would help the idle issue but no dice. No miss fires or pending codes here either, throttle body is clean as a whistle.

 

[mcc]

Sorry for the very late reply.

Since posting my Envoy's started having issues with the AC cycling on/off more rapidly than usual, causing rev dips each time. The "shudder" never went away but never got worse. The transmission has a bad history and is slipping more frequently now. It's got at least one warped rotor and the fan clutch is getting sticky. Top it off with a few minor electrical gremlins, a couple bad HVAC actuators and various clicks and squeaks in the interior. I'm sure there's more things I'm not thinking of right now.

It's within my financial means to move on to something new and I've decided to do so. A new '14 Mazda6 Touring will be rolling in for me soon. Thanks to all for their support! GMTNation has been a great resource and I've learned a LOT along the way.