Rough idle, lots of vibration, sluggish acceleration, shuddering at low speed

[TahoeFan224]

2014 Chevy Tahoe LT (rear wheel drive) with 170,000 miles,

Experiencing consistently rough idle, with lots of vibration, consistently sluggish acceleration, occasional shuddering at low speeds (under 15 mph). No codes, no check engine light.

https://www.amazon.com/Veepeak-Bluetooth-Diagnostic-Supports-DashCommand/dp/B011NSX27A

I have this ^ Veepeak OBD II scanner, but I am clueless when it comes to vehicles and I'm not sure what to make of the live data.

I put in new AC Delco plugs, wires, and coil packs, no improvement. Cleaned MAF sensor, cleaned throttle body, replaced air filter, no improvement. I tested the fuel pressure at the fuel rail and it seems to be well within spec, so I will assume the fuel pump is OK for now. I tried spraying carb cleaner around the hoses to hear if the engine revs up due to vacuum leak but it didn't seem to at all. There is no PCV valve on this thing from what I can tell and the PCV hoses & connections look fine.

I used "Gumout - All in One fuel system cleaner" when I filled up the tank from close to empty, and it did seem to idle smooth in the parking lot and ran decent on the drive home, (still a bit sluggish when accelerating), but began idling rough again the very next time I started & drove it.

The injectors have at least 130,000 miles on them, and may even be factory original (170,000 miles). So, they may be long overdue for replacement. Amazon has ACDelco GM OEM injectors for $55 each (nearly half the price of local parts place) on their ACDelco Amazon store (I assume that means these parts are genuine?) but before I spend $470 on 8 new injectors, I wanted how to rule out whatever else it could be (O2 sensors, catalytic converter, etc.?), and would love to know how exactly to test before I throw any more parts at this problem.

Any idea how to troubleshoot from here? Thank you for your time!

 

[Foggy]

Without any codes present or even more info like a scan tool log file, it would be
unwise to buy a set of injectors.. And I wouldn't buy them from amazon- lots of fake
imposter parts there. You need to buy parts from a "non third party seller" like
summit racing or rockauto . Lots of "brand name" knock off parts going around.

I would suspect a MAF or throttle body to be out of whack that would cause
rough running... A vacuum leak would, but usually if it's that bad a lean code
would come up

DOD lifters going bad will cause issues too, but will generally throw a misfire code
on the cylinder that is affected.

Where did you get your AC Delco plugs and Wires ????
I've never heard of all coil packs going bad at the same time, so that was
probably a waste of money... It's unusual for them to go bad at all - even just 1

 

[Doubeleive]

I wouldn't be concerned with the injectors at all, if it is a concern you can have a injector service done for about $80
like Foggy Said your issue is more likely air related, (maf/TB)
shuddering could be torque converter

 

[OR VietVet]

When you cleaned the throttle body, did you remove and made sure you cleaned front and back and did not move the throttle during this process? You may have been on the right track on the repair but if you moved the throttle plate, the system has to relearn and what you experience during this can be some of the same symptoms. But you said you did the fuel fill and seemed to smooth out and then problems started all over again and a relearn does not do that, I think? Never had to do a relearn so unsure if symptoms come and go and come back again or they just gradually get better until relearn is done. No CEL sucks.

WAG here, Remove both battery cables and leave apart for 15 to 30 seconds and then touch them together for about 1 minute and reattach at battery and see what happens. In one form or another, I have seen this recommended for strange happenings here and saw where someone recommended this. maybe not the same way I just laid out but in some fashion anyway.

 

[TahoeFan224]

Well, it was worth a shot, thanks for your input fellas

 

[yukon06]

I'll throw in my .02 for what its worth...
I have a VW cc in my driveway and all the symptoms you describe...I replaced everything you said plus a few more before I took to a shop and had it on machine came back bad intake runner position which is a bad manifold on that car, intake runner flaps go bad and its a manifold recall though im past the recall and doing it myself....

 

[91RS]

If no codes, engine mounts and a transmission are my guess.

 

[Chris Mosher]

2014 Chevy Tahoe LT (rear wheel drive) with 170,000 miles,

Experiencing consistently rough idle, with lots of vibration, consistently sluggish acceleration, occasional shuddering at low speeds (under 15 mph). No codes, no check engine light.

https://www.amazon.com/Veepeak-Bluetooth-Diagnostic-Supports-DashCommand/dp/B011NSX27A

I have this ^ Veepeak OBD II scanner, but I am clueless when it comes to vehicles and I'm not sure what to make of the live data.

I put in new AC Delco plugs, wires, and coil packs, no improvement. Cleaned MAF sensor, cleaned throttle body, replaced air filter, no improvement. I tested the fuel pressure at the fuel rail and it seems to be well within spec, so I will assume the fuel pump is OK for now. I tried spraying carb cleaner around the hoses to hear if the engine revs up due to vacuum leak but it didn't seem to at all. There is no PCV valve on this thing from what I can tell and the PCV hoses & connections look fine.

I used "Gumout - All in One fuel system cleaner" when I filled up the tank from close to empty, and it did seem to idle smooth in the parking lot and ran decent on the drive home, (still a bit sluggish when accelerating), but began idling rough again the very next time I started & drove it.

The injectors have at least 130,000 miles on them, and may even be factory original (170,000 miles). So, they may be long overdue for replacement. Amazon has ACDelco GM OEM injectors for $55 each (nearly half the price of local parts place) on their ACDelco Amazon store (I assume that means these parts are genuine?) but before I spend $470 on 8 new injectors, I wanted how to rule out whatever else it could be (O2 sensors, catalytic converter, etc.?), and would love to know how exactly to test before I throw any more parts at this problem.

Any idea how to troubleshoot from here? Thank you for your time!




View attachment 384877

I just went through this same issue on my 2015. Replaced the MAF, and both PCV hoses and cleaned the throttle plate. Once relearn was done it runs perfectly again. Took couple days for relearn after I unhooked battery and cleaned the throttle plate. Original code was 0172 and I replaced all 4 oxygen sensors first. The rough idle didn’t go away after that so I knew it was time for new MAF and the hoses at 140k

 

[scruffy]

You didn't say (unless my speed reading was shot) what fuel..I've had flex fuel put me through the paces and abandoned it for a year now with perfect results (with the exception of 'mo money)-she will always be my baby!

 

[NardDog]

Have you looked at the motor/trans mounts and driveline yokes