[wixomhead]

Happens when coming to a stop AND at highway/cruise speeds - when I tip in the throttle AFTER taking foot completely off throttle - on hwy this feels like a transmission/lock up converter hesitation but my gut tells me related to former issue. Feels like maybe MAF/vacuum prob? Recently sprayed/wiped cleaned throttle body w carb clean and sprayed MAF w MAF clean.

No codes. Idles like glass once it recovers from the dip down to 500rpm. Strong and smooth acceleration. No noticeable change in mileage (20+ hwy). Just got back from 200 mile highway ride. Getting worse. 120K mikes, would suspect coils BUT see above.

Have searched this forum and the web several ways but unable to find a solution, anyone solve for this?

 

[NorthernSRX]

Was the condition present before you did the TB and MAF cleaning?

 

[TheFlash]

how many miles on the car? what maintenance have you done?

 

[NorthernSRX]

how many miles on the car? what maintenance have you done?

I think it has 120k miles.

 

[TheFlash]

if 120K plugs should have been changed a long ago. has any gas additive been added?

 

[wixomhead]

Team - thanks for all the quick replies!

120K miles. I've owned, maintained and mostly repaired it myself since 40K.
Changed plugs @ 90K - AC Delcos, whatever was factory
87 fuel always and everywhere, no additives.
I need to check air cleaner, it was very clean last time I checked it but who knows.
I replaced alt, battery and water pump 1000 miles ago. Ran fine since then until now.

I just started it cold now - idled at 1500 as usual, down to 750. A few misses, there is a 1 or 2 good misses, and very mild consistent vibrating/missing happening.

 

[Lifespeed]

Engine vibration felt through the chassis is often caused by bad hydraulic motor mounts. Worn timing chains and cam phasers can cause hesitation at throttle tip-in, particularly on the LLT engine. Not sure if that is what you're describing.

 

[wixomhead]

@Lifespeed - Thanks for the input on mounts and timing hardware. Will consider this.

@NorthernSRX - This condition was not present prior to cleaning MAF. THe condition did not occur until 1000 miles after cleaning MAF

@TheFlash - I just replaced water pump and alternator roughly 1000 miles ago. Car ran fine for 1000 miles until last night.

@Today: After driving 200 miles home last night, I came to a stop int he garage with brake on. Engine stumbled as usual down to 500 or so and then back up to 700 or whatever normal is. Mild consistent miss as above. This morning car started fine and idled to 1500 as usual, missed once or twice, settled at 700 or whatever normal is, consistent, mild miss. I opened up the airbox to check filter and air intake to throttle body and found this...puddle?. Tastes like ... coolant (!?). Box looks as expected, filter looks pretty clean to me.

 

[TheFlash]

The correct idle speed at operating temp. for DI engine is 500-550 RPM. Did you gap all the plugs? or just put them in?

You need to do a code reading and see what is there. I have sometimes seen a poor injector that will clean up after two tanks full and bottles of
Chevron Techron Concentrate Plus Fuel System Cleaner - 20 oz.

A little throttle body cleaning will help too.

at that mileage, you may see some carbon build-up on the intake valves. Puts a vacuum gauge on the intake and get some vacuum readings.

 

[Lifespeed]

You haven't stated which engine you have. Ignition coils are known to fail on these cars, a scanner will advise as to the extent that misfire is a problem. I don't advise just changing the one coil the scanner identifies, not only because cylinder identification isn't always accurate, but because the coils tend to have problems at a similar age. I like the BlueStreak ignition coils, good price and a good track record in the VSport community.

Misfire is often a different problem from hesitation at throttle tip-in. It is possible you have one of these problems, or both. When you depress the throttle at low RPM, asking for moderately high load, and the engine misfire and jerks (low RPM high load is common regime to misfire) that would be a misfire problem, as opposed to hesitation where the engine doesn't respond immediately to throttle, rather it exhibits a delayed response, then surges. It is helpful if you can identify the difference, as the causes are different.

 

[wixomhead]

THANKS for all the quick replies/advice. Some updated info:

The correct idle speed at operating temp. for DI engine is 500-550 RPM. Did you gap all the plugs? or just put them in?
You need to do a code reading
A little throttle body cleaning will help too.
Put a vacuum gauge on the intake and get some vacuum readings.

Gap plugs? Do people still do that? I put new plugs in 30K ago. Can't recall if I gapped them, I doubt it. Can/will check again.
I don't have a tach instrument, but by ear / dash tach the idle hasn't changed in 6 years I've owned the car, tach dash sure looks like 750 but must be lower than that I am certain.
No CEL, no codes showing up on my $39 el cheapo code reader. What reader should I upgrade to please?
I sprayed/wiped the top and bottom of the throttle body and plate with throttle in wide open position 1000 miles ago - did not remove T Body
Put vac gauge on port to right of engine - the one that connects to intake hose - but negligible vac reading coming out of there at idle (1-2) . I searched but other than brake booster could not find another port/help?

You haven't stated which engine you have. Ignition coils are known to fail on these cars, a scanner will advise as to the extent that misfire is a problem.
Misfire is often a different problem from hesitation at throttle tip-in. It is possible you have one of these problems, or both. When you depress the throttle at low RPM, asking for moderately high load, and the engine misfire and jerks (low RPM high load is common regime to misfire) that would be a misfire problem, as opposed to hesitation where the engine doesn't respond immediately to throttle, rather it exhibits a delayed response, then surges. It is helpful if you can identify the difference, as the causes are different.

2013 CTS Luxury 3.0
Car has always had a very brief, slight, funny, single misfire feeling when applying the throttle at 45MPH or so. Not a hesitation, not a stumble, just the slightest of delay which always made me think of a torque converter lockup hiccup when in 6th gear doing to 5 or etc - nothing that I felt needed attention as it's felt the same for 6 years 80K miles. Maybe this is coming back to bite me, dunno.

 

[NorthernSRX]

I'd be replacing that air filter for sure - it's not clogged but it's dirty and has to be restricting air flow at low vacuum. Also check for the negative side engine breathing tube (just after the MAF) and check for tightness on both the duct and engine ends.

Liquid in the duct between the MAF and the negative side breathing tube is super weird. Check to see if your PCV barb is clogged as your block may be breathing in through leaks and out through the in tube. It shouldn't but I've seen it before on (very) old V6s and it definitely screws up the idle.

 

[silversport]

a minor concern but there are quite a few leaves in your airbox...is it possible that you haven't properly closed and resealed your airbag and your MAF is picking up some air leakage through that???...I know that sometimes after checking the air filter it seems that the airbox lid hasn't made proper contact/closure on my 3.0 causing me to try, try again...

as for the ever so slight stumble at 45 MPH, is that when your transmission is going into overdrive???...I seem to recall that is either a gear change or overdrive right about that speed...have you tried putting your gear selector to the right (Sport Mode) and just driving that as if it were Drive but not manually changing the gears to see if that changes the feeling at 45 MPH at all???

Good luck,

Bill

 

[Padgett]

Stumble when going into OD/lockup at 45 is typical ignition misfire issue. Test $06 should tell (toward the bottom)

 

[Lifespeed]

First confirm misfire with a scanner. Then replace and gap the plugs, and inspect for signs of arcing or tracking. 30K miles is plenty, why would you pull the plugs out to check the gap without installing new parts? I used NGK 91276 LTR6AHX Ruthenium Dual Fine Electrode on my 2009 LLT with good results, don't know if your newer 3.0L uses the same heat range plug. I prefer precious metal on both sides of the gap for longer life, I noticed the OEM plug steel ground electrode burns away pretty quick.

If you still have misfires after changing the plugs, replace the ignition coils.

 

[wixomhead]

Great replies thanks all.

.5 Car idles at 550 in drive w brake applied

1. After removing and spraying the MAF with half a can ...... the 1/2 second stumble blip at idle after stop and 45 MPH OD skip is gone (for today). Based on this I am rejecting motor mount and cam chain etc cause.

2. The airbox was buttoned-up properly. The air filter is less than 10K old. The leaves/dirt do not concern me, that's normal for the fresh air side of the filter in my experience. I re installed properly/fit.

3. I need to find a scanner with $06 to live data the 6 coils. I might need to spend the ????$150???? help please

4. I have not had time to pull / inspect the 30K AC Delco OEM plugs. This weekend, maybe.

5. I made sure the vac line going from intake side of MAF to top rear of engine is seated properly and not ... obviously damaged.

6. Still some random arbitrary missing at idle but FAINT, nothing like Sunday night when it felt it would die/stoplight/45MPH OD stumble.

7. The drops of coolant on the MAF side of the intake tube - so random. I can only guess thatvwas some artifact of water pump job 1K miles ago; zero evidence of coolant anywhere near the throttle body, no smell of coolant in the cabin, exhaust, front end, under hood etc.

• • •

Will check gap/check for fouling plugs/find $06/report back. Welcome Autel or other scanner purchase advice, too - I need to upgrade my $29 foxwell odb code reader.

Thanks again, team

 

[Padgett]

Is this a good time to mention that Torque Pro ($5 on Android) and a $13 BT OBD-II mini (to avoid knees) dongle can not only do a $06 just if on a phone can e-Mail to you.

 

[Lifespeed]

1) It was never stated that motor mounts cause misfire, but that they transmit engine vibration to the chassis when failed. This remains true regardless of fixing the misfire, and at 120K they're almost certainly toast. I think it is unlikely MAF-spraying fixed a misfire, if that is indeed your problem. You'll know soon enough.

4) Inspecting spark plugs, while useful, cannot rule them out as a cause of misfire. The only way to be sure is to replace them.

 

[wixomhead]

Is this a good time to mention Torque Pro ($5 on Android) and $13 BT OBD-II mini can not only do a $06 just if on a phone can e-Mail to you.

YES IT VERY MUCH IS. AWESOME

@Lifespeed Thanks for helping me to understand the difference.

 

[Joseph Upson]

Happens when coming to a stop AND at highway/cruise speeds - when I tip in the throttle AFTER taking foot completely off throttle - on hwy this feels like a transmission/lock up converter hesitation but my gut tells me related to former issue. Feels like maybe MAF/vacuum prob? Recently sprayed/wiped cleaned throttle body w carb clean and sprayed MAF w MAF clean.

Disconnect your battery to clear baseline fuel trim corrections, then perform the idle/throttle relearn procedure.

I didn't see where you stated clearly that the symptoms were present before cleaning the MAF and throttle body, so I'll mention that some GM vehicle are notorious for misbehaving after cleaning the throttle body, especially if it was very dirty. Here's my recent experience.

Last week, I replaced the remaining high mileage sensors following the timing chain job on my Mom's car. This involved the MAP, MAF and throttle body, with AC Delco/GM parts on an 07 LY7. Immediately on startup there was a high idle that would not relent. I followed the idle relearn procedure on the instructions included with the throttle body, which also mentioned checking to make sure the car had the latest GM PCM programming. I searched and found a number of GM vehicle related threads on, "I cleaned my throttle body and now the car will not idle right".

I also followed the Rockauto, GM oriented idle relearn series and finally succeeded at getting the idle to consistently settle at the commanded rpm, by reinstalling the original throttle body. My Tech 2 clone revealed some amazing capability, to include changing the factory idle setting and TPMS pressure warning range and I'm sure some other options I have yet to discover, but I suppose it works best when everything is working as it should with the car, as I could not get the car to respond to it as desired. It's possible the new throttle body has a higher flow rate, I'll have to take measurements for comparison. The transmission did not shift efficiently either while the idle malfunction was present, it was grabby during down shifts, holding on to gears too long.