Rough idle/ volt drop

[Jscott]

Hello friends. Another one for you. My 1990 cutlass 3.1. Has a rough idle when it warms up. Replaced a lot of items and even a charcoal canister. Thinking the evap is bad. Which it was anyway. But the car starts acting up when it’s in gear and idling with foot on brake. Which I also noticed as my foot is on brake the engine kinda surges and I see my volt gage dip up and down a little. But enough to make the engine not perform as it should. I have to mention that I have a power master 3 brake system. Not a fan. Any ideas would be appreciated. 

[briskshovel88]

 

Jscott said:

Hello friends. Another one for you. My 1990 cutlass 3.1. Has a rough idle when it warms up. Replaced a lot of items and even a charcoal canister. Thinking the evap is bad. Which it was anyway. But the car starts acting up when it’s in gear and idling with foot on brake. Which I also noticed as my foot is on brake the engine kinda surges and I see my volt gage dip up and down a little. But enough to make the engine not perform as it should. I have to mention that I have a power master 3 brake system. Not a fan. Any ideas would be appreciated.

 

That Powermaster can load the electrical system pretty hard when it cycles, and the voltage dip could be dragging the idle down with it. A weak ground or tired alternator would make that whole combo a lot more noticeable.

[Jscott]

Thank you for your advice!! I really appreciate it. 

[Amanita]

On 9/24/2026 at 9:16 PM, Jscott said:

Hello friends. Another one for you. My 1990 cutlass 3.1. Has a rough idle when it warms up. Replaced a lot of items and even a charcoal canister. Thinking the evap is bad. Which it was anyway. But the car starts acting up when it’s in gear and idling with foot on brake. Which I also noticed as my foot is on brake the engine kinda surges and I see my volt gage dip up and down a little. But enough to make the engine not perform as it should. I have to mention that I have a power master 3 brake system. Not a fan. Any ideas would be appreciated. 

If you turn the headlights on and apply the brake do you notice any of the needles wiggle a little bit? I had that happen to me while driving and it turned out to be the alternator going bad, had to swap both that and the battery.