Engine pulsates during idle and from second to third gear

Idle air control motor. Clean it or replace it.

It could be many sensors, before you do anything check it with a good scanner

Replace the Intake Air Temperature Sensor.
Depending on your size Engine (2.4L, 3.0L or 3.3L) It should be located where the Air Filter is. When you take the cover off, it wil be mounted into the cover. It has the only wires going to the cover.
This sends information to the Computer which adjust the air/fuel mixture - causing surges.
The 2nd recommednation: to remove, clean and check is the Idle Air Control (IAC) Valve and replace if necessary.

Let me know if this helped....

Mine had a *bad*, but intermitent engine shudder (like it was running out of gas) between 30 and 40 mph. After 3 trips to the dealer, it finally did it in front of them. It's quite dramatic, so they admitted that I wasn't just bringing it in for fun and started guessing what was wrong. They found a TSB that recommended starting with one of the O2 sensors, which fixed it perfectly, immediately.

Sounds like yours isn't your engine - but I thought I should say something just in case.

Ok there are several options such as water in the fuel or dirty fuel for starters. Another option would be clogged fuel injectors or a dirty map sensor. Check the spark plug wires to be sure that they are on tight and none are worn at contact points such as rubbing against a sharp edge. Let us know what the code(s) say.

check the iac valve

Sounds like a vacume line or O2 sensor has failed.

try changing distributor cap & coil

My fathers did the same thing. we soon figured out that the injectors were not making an even mist of fuel they were just dumping the fuel in. we replaced the injectors and the problem was fixed.

I will be trading in car or fix by dealer . NICO club more helpfull thanks anyway.