RPM's fluctuate

Tiny
THEBECK60
  • MEMBER
  • 2000 CHEVROLET IMPALA
  • 3.8L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 100,195 MILES
Shifts good, no codes but between 40 and 50. The rpm's fluctuate a couple hundred rpm's up and down. Changed MAF, IAC, TPS, speed sensor, no prevail. It only does it between those speeds. Highway speeds are good. Have been doing a lot of soul searching and came up with a lot of different remedies. Driving this backyard mechanic bonkers.
Saturday, December 21st, 2019 AT 7:00 AM

1 Reply

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi,

Since it is happening only at that speed, it leads me to think it is related to something other than the engine. The engine doesn't know the car's speed. If it was a specific RPM where you notice it, it would do it at any speed but specific to a set RPM.

Pay attention to see if when you feel it correlates with a specific gear the transmission has shifted into. Also, if you have a live data scanner, I need you to check the short term fuel trims when you feel it happening (throttle steady).

Let me know.

Joe
Was this
answer
helpful?
Yes
No
+1
Sunday, December 22nd, 2019 AT 7:37 PM

Please login or register to post a reply.

Related Engine Revs Up Content

Idle Air Control Motor Replacement
GUIDE
Idle Air Control Motor Replacement
The idle air control motor or idle speed control motor is designed to adjust the air flow into the intake manifold at engine idle. Engine idle speed is monitored by the PCM...
VIEW MORE