Hesitation/stumble at 50 mph fixed by racing engine on highway but new sound

Ariel Guerra

Original poster
Member
Jul 11, 2012
17
Ok so my '02 Envoy, which I've had since showroom, has 198,000 miles on it and a couple of weeks ago it started to hesitate/stumble when I would get to 50 mpc. It would be that way until I got to about 60 or so. I wondered if I got bad gas in it but that was two fill ups ago so yesterday I figured I'd floor the pedal to rev the engine on the highway to see if that would do anything. It helped a good amount in that it doesn't hesitate/stumble when slowly going through 50 to 60. What I do notice now though is that the sound the engine makes is like it's muffled, but I honestly don't know if it's always sounded like that or I'm noticing it because the stumble brought my attention to that speed reading.

And if anyone knows, did my racing the engine help clean out gunk in the injectors or help the throttle body butterfly loosen?

Sorry it's so long and thanks for any info or help.
 

Ariel Guerra

Original poster
Member
Jul 11, 2012
17
jsheahawk said:
Hmmmm.

If you put it in third and accelerate (eliminating overdrive), does it still hesitate?

Jared

Don't know but I'll try that after work and get back to you.

By the way, any idea why the engine seems to sound muffled when accelerating smoothly from 50 to 60? Or is that normal and I'm just hearing it for the first time?
 

jsheahawk

Member
Jan 16, 2013
533
Kansas City
Ariel Guerra said:
Don't know but I'll try that after work and get back to you.

By the way, any idea why the engine seems to sound muffled when accelerating smoothly from 50 to 60? Or is that normal and I'm just hearing it for the first time?
Mine sounds a little quieter accelerating through the 50's, but nothing drastic.

Jared
 

Ariel Guerra

Original poster
Member
Jul 11, 2012
17
jsheahawk said:
Mine sounds a little quieter accelerating through the 50's, but nothing drastic.

Jared

I guess maybe that's the the gears shift and the RPMs go a bit lower.

Thanks for the help Jared, I'll get back to you tonight here.
 

Ariel Guerra

Original poster
Member
Jul 11, 2012
17
jsheahawk said:
Hmmmm.

If you put it in third and accelerate (eliminating overdrive), does it still hesitate?

Jared


I did this last night and it still hesitated.

What's weird is that for the most part it will hesitate exactly at 50 mph, and yet once a whiel it won't, especially if I'm accelerating at a faster pace where the RPMs are higher.

Could it be the Throttle position sensor that's gone bad and has a dead spot that's causing me grief?

I replaced it once 4 years ago almost to the day, and 60,000 miles later. I bought it from the dealer and didn't think it would go out so soon, especially since the original one lasted 135,000 miles.
 

jaguarjoe

Member
Nov 22, 2012
73
In Jaguarland you do an "Italian tune up" to your V12: put it in 2nd gear, floor it and drive it like you stole it. After about 20mins, it'll run smooth as butter.
You could put a stick shift V12 in 5th gear, start the engine, leave it in 5th, feather the clutch, and go from 0 to 160mph without ever shifting.
 

jsheahawk

Member
Jan 16, 2013
533
Kansas City
Ariel Guerra said:
I did this last night and it still hesitated.

What's weird is that for the most part it will hesitate exactly at 50 mph, and yet once a whiel it won't, especially if I'm accelerating at a faster pace where the RPMs are higher.

Could it be the Throttle position sensor that's gone bad and has a dead spot that's causing me grief?

I replaced it once 4 years ago almost to the day, and 60,000 miles later. I bought it from the dealer and didn't think it would go out so soon, especially since the original one lasted 135,000 miles.
Hmmm...I was really hoping someone more knowledgeable would jump in by now!

Did it have the same symptoms when it went out the first time?

jaguarjoe said:
In Jaguarland you do an "Italian tune up" to your V12: put it in 2nd gear, floor it and drive it like you stole it. After about 20mins, it'll run smooth as butter.
You could put a stick shift V12 in 5th gear, start the engine, leave it in 5th, feather the clutch, and go from 0 to 160mph without ever shifting.
Yeah, that works well in diesel trucks, too. Not doing 160, but...yeah.

Jared
 

TangoBravo

Member
Dec 5, 2011
208
jsheahawk said:
When was the last time that you cleaned the throttle body?

Jared

Ariel Guerra said:
About a year ago.

This doesn't raise a red flag to anyone else. I know for a fact that mine certainly can not go a year without cleaning, more like every oil change.
 

CaptainXL

Member
Dec 4, 2011
2,445
Hesitation could be plugs, wires or coils. Check the plugs and replace if needed with Iridium. Do you have a Check Engine Light on/flashing? Bring it to Autozone or Advance Auto and see if there are any codes. We know zip about what maintenance has been done thusfar so you need to start somewhere.
 

gmcman

Member
Dec 12, 2011
4,658
Does the muffled sound resemble a deep, throaty, wide-open carb sound? Mine would make a deep throaty sound when the CPAS was going out.

I would flat-foot the accel pedal from a stop and watch the mirror for a cloud fom the exhaust....I do this every so often. Run 2nd gear to the 6K mark if feasable.

Could be some crud, could be old plugs and dirty TB. Does the tach needle jump around when this occurs?
 

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