I have a 2004 Monte Carlo LS and I noticed that while driving at a constant speed on flat road, the RPMs randomly shoot up to about 500 RPMs or less and goes back down to normal. I asked my local mechanic what he thinks it is and he said it could be cylinder misfire. I did change the spark plugs and wires before this problem began. On the other hand, my dad thinks that I could be losing a gear on my transmission. Should I spend the money to put it on a computer and test it for cylinder misfire? Or should I take it to a different mechanic and get another opinion? Anyone else have any opinions to help diagnose my problem?

 

The check engine light will come on and a fault code will be logged when your engine misfires. I have an ultra gauge (cheap) connected and reset my CEL check engine light when mine does that. Sometimes I check the computer for pending faults before they trigger the CEL. It takes a while to trip the CEL. A cylinder 1 misfire will log P0301, cyl 2 P0302, cyl 6 P0306.

Revisit the work you did. maybe a plug cracked when you tightened it. or a wire could be not routed / seated right.

 

Put the car in 3 and see if it does it still.

I think you are jumping in and out of torque converter lock up.

 

Something to consider is that it doesn't act up every time I drive it. Every once in a while it will do it. And I don't have a check engine light on either

 

I ended up putting it on the tester and it brought up code P1811, which involves the transmission. I'm really don't know much about this code so if someone could give me some insight, that would be great

 

The dreaded P1811 code is listed as this

DTC P1811 Maximum Adapt and Long Shift

My car started getting that and I was able to get over 100 000 kms out of the transmission before it finally went on me. You may want to look into having the shift solenoids changed as they are a common fail point within our trannies you can buy them at
ZZPerformance | 3800 Performance Parts | Largest Aftermarket Supplier!
and have a local tranny shop replace them for you, or start putting money away for a new tranny, or a used one. Sometimes if you change the tranny fluid and filter, don't flush the tranny, just change the fluid and filter and put in some tranny slip fix it may clear it up for you, the lucas oil brand seems to work good.

 

Here is a link to a post made by another member with all the trouble codes listed and what they mean.


https://montecarloforum.com/forum/fw...de-list-17144/

 

I changed the transmission fluid and filter last summer. I was thinking about adding a quart of that transmission fix to it and see what it does. Thanks for the help!

 

So if I change the shift solenoids before it goes out, will that prevent my transmission from going out?