Tach fluctuates 300 Rpms in 4th Gear bewteen 40-50 mph
 

The engine speed does not appear to be changing and I hold the speed steady at 40 or 45 mph and the tach is bouncing up and down 1200 to 1600 rpms. It appears to do at this at 60 mph as well.

If I put the car in 3rd gear at 40 mph, the tach is steady @ 2,000 rpms.

It is an 06 Monte Carlo LS with a 3.5.

Anyone else seen this? The tach seems fine at speeds below 40 mph, but I do not notice this behavior all the time above 40 mph.

Thanks!

RE: Tach fluctuates 300 Rpms in 4th Gear bewteen 40-50 mph
 

sure its not just the TCC goin on and off?

RE: Tach fluctuates 300 Rpms in 4th Gear bewteen 40-50 mph
 

TCC? Not sure. What do you mean?

Thanks.

RE: Tach fluctuates 300 Rpms in 4th Gear bewteen 40-50 mph
 

torque converter clutch, keeps the converter from sliping and improve mileage. it may engage it, but then at 1200rpm theres not enough power down there and at the slightest increase in engine load, then has to disengage.

if the tach is jumping up as engine load increases, and dropping down as engine load decreases, this would be perfectly normal.

RE: Tach fluctuates 300 Rpms in 4th Gear bewteen 40-50 mph
 

So is this normal? I am keeping the throttle a one speed crusing 40 mph in overdrive. Drop it into 3rd manually and the needle sits steady close to 1800-200 rpms.

Thanks.

RE: Tach fluctuates 300 Rpms in 4th Gear bewteen 40-50 mph
 

How many miles are on your Monte and have you had a trans service done? If it's at like 30,000+ TRY A TRANS SERVICE and see if that keeps the TCC from slipping, this is NOT normal. A trans service could be needed because dirty fluid will cause this too.

RE: Tach fluctuates 300 Rpms in 4th Gear bewteen 40-50 mph
 

There is 10,000 miles on the car. I first noticed this at about 6500 miles. It does not occur every time I drive the car. Once it a great while there is a hestitation "jerk" coming out of overdrive below 20 mph.

I will take it in to the dealer early next week. Any one else seen this?

Thanks much!

RE: Tach fluctuates 300 Rpms in 4th Gear bewteen 40-50 mph
 

Warranty?? I HOPE!! :o)