Volvo 940, Non-Turbo

When I start my car in the morning, the RPM goes up beyond 1K (for about a second or two) and then come back down to about 800. It'll idle okay but when I shift the gear from P to D, the car will shake and rock for a while before it steady out. All this while I had my foot on the brake.

What could cause it, brake pump, fuel pump, FPR, transmission mount?

Thanks in advance for all advice and instructions.

Laozong

Try putting it in reverse to see if it does the same thing.
Bob

Thanks Bob for your suggestion.

I now have a better diagnosis but not the solution.
This morning, I opened the hood and started the engine. I notice that without shifting the gear, the engine would rev up high and then lowered itself again. It did that twice before steadying out to normal idle. Each time when the engine RPM dropped, the car would then rock.

Any ideas?

Thank you.

Laozong

When it first starts, it will normally go up around 1000 rpm, then settle down. The rocking indicates that either the idle is affected by dirty throttle body (low idle) or perhaps your motor mounts are worn.

The situation is like this:

After the engine starts, it will rev up to 2K then down to 450(thats when the car shakes) and then up again to 2K, down once more to 450 and then steady out at 800-900.

I know this is not normal because I only experience this recently.

Thanks.

Laozong