So I have an automotive degree and am ASE certified and still can't figure this out. When the car is in drive, brake pressed with a/c on the car vibrates terribly. I am starting to notice it even when the A/C is not on. I have changed spark plugs, rear engine mount and sea foam through intake manifold. I cleaned the throttle body as well. I have a header and intake but it ran fine for a long time once these were installed. I only run high octane gas and synthetic oil. I have talked to dealerships and no one has an answer. I have checked all vacumn lines and could not find a leak. The car once above 1000 rpms runs excellent. Please help, I can't afford to pay a dealership.

 

Are you positive the front and side engine mounts are in good condition?

 

Also, does your RPM drop when the brakes are applied or it's still hovers around 750RPM?

 

I second the engine mounts......

 

Engine mounts, a possibility.

Also spark plug wires.

 

You don't mention a Check Engine Light. Are there any codes?

Checking Long Term Fuel Trim (LTFT) and Short Term Fuel Trim (STFT) may suggest a source of rough idle. An OBD2 scanner w/ capability to monitor some sensor info is req'd.

High +LTFT would suggest a lean condition, vacuum/intake leak or inadequate fuel delivery (fuel pressure, injector blockage).

High -LTFT would suggest a rich condition; air restriction, exhaust blockage, or excess fuel (leaking/sticking injector).

All of above can cause rough engine. Is engine missing or simply erratic idle?

good luck

 

Sorry for the late reply. The engine rpm drops to 600rpms when in drive and thats when the noise and shaking starts. The brakes depressed or not does not change symptoms. I have replaced spark plugs with the best possible ones. It is direct ignition so there is no spark plug wires. The side engine mount looks a little dry rotted. I have applied pressure to it when it has the issue and nothing changes. If I look at the mounts when this problem occurs, they are not moving at all. The front mount looks ok as well. The transmission and block don't look like they are moving anywhere near as much as the head...probably because they are connected to the mounts. I have a scan tool but it doesn't give me the fuel trim for some reason on acuras, only other mfgs. There is no check engine light on either, that would be great if there was. I feel like it is either a vacuum leak or electrical issue. I have checked all vacuum lines and do not see any cracks or hear a leak. I really hope i dont have to have a dealer look at it...but I am getting desperate. I appreciate the input and any more would be great. Thank you all

 

Idle speed is directly controlled by throttle plate position. A very dirty throttle plate might cause low idle problems.

To clean you will need to turn key to On and have someone open throttle plate w/ gas pedal to clean.

good luck

 

are the RPMS staying flat at one speed? Are the RPMs jumping up/down?

does the problem occur in drive and in neutral?

If the vibration is occuring and the RPMs are stable, then it's probably motor mounts.

If the the RPMs are jumping causing the vibration, then you have a air/fuel/spark problem.