RPM Stumbling When Stopping

[Yelbom15]

Hey, so I tried doing my digging but really couldn’t find any that was similar to me.

I’ll be driving, stop light ahead, push in the clutch, take it out of gear, return the clutch and as I’m coming to a stop, the RPMs drop as if I’m still in first trying to kill the engine. It drops, shutters and then just goes back to normal like nothing happened. Other than that, engine runs as fine as I can tell.

This only happens when leaving work the first couple stops. After that, all good.

Clutch bleed?

 

[Intuit]

Weird. If you're in neutral and releasing the clutch, there shouldn't be any drag. (other than the initial spin-up or speed-match of the input shaft) Check for codes. If it's something sensor or servo related that affects its ability to idle then a code(s) should be present for it. Can also pull and read the plug gap + condition.

Only thing I can think of is a throw-out bearing but those tend to be noisy when failing? Fashion a dipstick of sorts, level the car, unscrew the refill bolt from the front of the transmission and get a level reading.

The clutch would be suspect if you had issues getting in/out of gear but your description if the issue doesn't include any such account. Does the car easily roll when in neutral? Do the front wheels easily roll with them up in the air, trans in neutral? No transmission differential swap?

 

[Yelbom15]

@Intuit No codes are present at this time as well as idle being perfect morning, day and night.

I had concerns about the “chatter” noise before. When I come to a stop(out of gear/clutch out), I do get chatter/clicks when coming to a stop. I had mixed responses so I just went ahead and ignored it. Going in and out of gear is fine besides the occasional random trouble getting into first but my VW did the same. No gears pop out under any load.
I recently changed the transmission fluid with 300. Chatter/clicks noises definitely died down but the random RPM drop is still there.

 

[Intuit]

When leaving work, give the car engine an extra extra long time to warm up (transition to closed loop) before departing. See whether the behavior ceases. Could be vac leak or is in need of a tune-up (plugs). (EVAP presents a controlled leak via fuel tank) What's your mileage?

 

[Yelbom15]

@Intuit I just hit 62,000. I’ve done the fluids for the engine and transmission within the last 500 miles and thought about spark plugs but held off for a bit thinking spark plugs this early wouldn’t give me issues.
As far as warm up, I usually wait until I hit two marks on the coolant gauge before I adventure off into my busy city traffic.
Today scared me a bit because it dropped, then went above 1k, then dropped again before it finally settled. I typically only see it drop, not shoot up like it’s trying to save itself.

 

[Sam4]

sounds like D2BZ-9C047-E. The poorly named 'tube fuel feed' gremlin.

 

[Intuit]

Yeah too early for plugs. Explore what @Sam4 mentioned. Could be a potential source for vac leak.

 

[Mega ST]

Is it always related to the clutch being released? Before replacing my PCV/EVAP lines mine did the same thing unrelated to the clutch of course. AFR will go full rich and car will stumble. Sometimes accompanied by a whining sound from the gas tank.

 

[Yelbom15]

@Mega ST I only say it’s related to the clutch because it begins only when rolling to a complete stop. Other than that, never happens. I could coast 100 feet, won’t tremble until I’m about to stop.
Best way I can explain is that it feels exactly like I’m still in first when coming a stop even though clutch is in or gear is set in neutral.
I’ll go ahead and replace that line a couple have mentioned. It seems like they go out anyways.

 

[Mega ST]

Weird. Possible pressure plate failure? I've never looked at the PP on these, but I had a spring break on a PP before and had something similar happen until it failed completely and would not disengage.

 

[Dpro]

@Mega ST I only say it’s related to the clutch because it begins only when rolling to a complete stop. Other than that, never happens. I could coast 100 feet, won’t tremble until I’m about to stop.
Best way I can explain is that it feels exactly like I’m still in first when coming a stop even though clutch is in or gear is set in neutral.
I’ll go ahead and replace that line a couple have mentioned. It seems like they go out anyways.

If it was clutch it woudl grab or slip if it slipped you would most likely smell it and or you revs would go up while acceleration stayed the same. It actually sounds like a possible crank angle sensor issue and yes I have had a car that did exactly what you are talking about right before the crank angle sensor took a dump. It’s not the end the world if it is that . They are not expensive and can be installed going through the passenger lower wheel area with the wheel off. It literally bolts into your front cover right by your lower front pulley.

 

[Yelbom15]

@Dpro That seems to make more sense. I was trying to wrap my mind around why it would give me issues when coming to a complete stop with it being a manual. It seems to make more sense if we were talking a torque converter issue on an automatic. Crank angle sensor. I’ll take a look at that.
Thank you.

 

[Intuit]

Air flow moving through the engine bay and around the vehicle changes along with its speed.