I have 1999 Maxima, 165k miles. As normal, the RPM usually shows over 1000RPM when engine cold then drops to normal 700 RPM after it gets warm. But now, it shakes when it first starts up. RPM shows little up and down. It only happened after the car sitting overnight or after 5-6 hours. If I press on the gas pedal then problem will go away. I recently cleaned the throttle body, MAF, IAC valve, replaced new spark plugs, new gas filter, new PCV valve, coolant temperature sensor but did not help. I also cleaned a EGR Guide Tube when it had an EGR malfunction trouble code at 120k miles. There has been no trouble code yet. The engine is running fine and very responsive as I have cleaned many parts. If anyone can help, I would appreciate it. Thanks.

 

If have rough idle after start cold engine, my first guess would be vacuum leak somewhere. Check vacuum leak.

 

+1 for checking for vacuum leaks..

How many miles do you have on your Max? Where are you located for parts reference purposes?

Are you getting any check engine codes? Have you recently cleaned the EGR pipe and valve assembly?

My 99 model suffered with a hard to start, rough idle, RPM bounce issue that couldn't figure out until I finally got a code for the EGR valve. It felt like an intermittent vacuum leak but I had replaced all vacuum hoses and double checked for a vacuum leak with no luck.

It turned out the EGR valve was not closing properly which was allowing an intake system vacuum leak to cause symptoms listed above. I had cleaned the EGR pipe and temp sensor some weeks earlier so I knew everything should have been working.

The 99 model uses an electric EGR valve like the picture below.

In my case, I purchased a new BWD Intermotor EGR valve for $92.99. The car started up and idled like a new one. I couldn't believe the difference a new EGR made. The BWD Intermotor EGR uses the same Hitachi part that is in the picture of the OEM unit below.

If it turns out that you need a new EGR valve, here are some EGR valve and pipe pictures below and in the following slide show.

http://s286.photobucket.com/user/Rid...axima/1999/EGR

 

The engine could be shaking due to the fact you are loosing fuel pressure when the car sits overnight. Check your spark plugs to make sure that none of them are fouled from a bad fuel injector that could cause the fuel pressure to leak. Also for me it was a bad fpr that causes shaking after sitting overnight that would not hold the fuel pressure anymore and when I gave it gas the shaking would disappear.