Car needs tuning/repair. But whats wrong? Heres whats going on....

[alkemist]

Hello,
I own 96 Riviera no SC with engine at around 76k miles.

REcently, I noticed a distant change in idle manner of the car.

Now when it idles below 1000 rpm, it feels, a little, as if the engine is idling rough. And I personally feel the engine emitts more bass in the feel and sound.

I have Actron super scanner if that would help solve the issue



I wonder what I should try to do.


I need to change oil. Could that solve it?

Besides that the engine is in very well maintained condition.

[HotZ28]

First, I would check the complete exhaust system for leaks, to determine if the "bass sound" could be coming from that area.
When the OBD II system detects a misfire that exceeds "normal" limits, it illuminates the Check Engine light and sets a P-code that corresponds to the misfiring cylinder. The last number in a P300 series code tells you which cylinder is misfiring. A code P304, for example, says cylinder number four is misfiring. At this point, you want to check the ignition secondary; i.e. coils, wires & plugs. If you also find a P204 code (P200 series codes cover the injectors), you'd know the misfire was probably caused by a bad injector.
If you find a P300 code, it means the misfire is random and is moving around from cylinder to cylinder. The cause here would likely be something that upsets the engine's air/fuel mixture, such as a major vacuum leak, leaky EGR valve or unusually low fuel pressure (weak pump or faulty pressure regulator). There's really no magic bullet for finding misfires. It takes a certain amount of detective work to isolate the fault and determine the underlying cause.

[96riviera18]

i would check the exhaust like HotZ28 said and you may try cleaning the throttle body or running sea foam thru the tank and vac lines. it may help or solve your rough idle problem. keep us updated on symptoms. could just be a bad tank of gas.

[alkemist]

Originally Posted by 96riviera18

i would check the exhaust like HotZ28 said and you may try cleaning the throttle body or running sea foam thru the tank and vac lines. it may help or solve your rough idle problem. keep us updated on symptoms. could just be a bad tank of gas.

The engine vibrates only when in Drive. NEU or PAR cause NO vibration.

Spark plugs, wires and injectors are OK
no misfire
Fuel pump and lines and pressure is OK
Intake manifold and throttle body are OK (cleaned)

[96riviera18]

could be a motor mount going bad, does the engine sit low (slanted right or left, or back?) does it shift ok?

[alkemist]

mounts are like new