My son's 95 Mazda626xl drives beautifully but it shakes and stalls when in idle or neutral position Do you know what the problem could be

Check your engine mounts, shaking and rattling could be vibration running in through the car= rubber perished on mounts.

Your idle air controller may be failing. Begin checking for stored codes using a code reader, and progress to standard troubleshooting steps such as checking spark, fuel delivery, and operation of the intake air control circuit.

Usually the problem is due to a dirty throttle body or a faulty idle air control valve. Stalling in reverse and not in drive is unusual.

The first thing I would have checked is the TPS, ( throttle position sensor ), this is usually the cause of a high idle.

As far as running bad and fake stalling or stalling, there are 2 very common things that can cause that.

1. MAF, ( mass air flow ), sensor. If this is faulty you will have issues like, bad idle, loss of power when accelerating, poor gas mileage, fake stalling and stalling, eventually your engine will not start.

2. Oxygen sensors. Faulty oxygen sensors can cause very similar symptoms as the MAF.

I hope this helps you.

I would check your "idle speed control" ISC on the intake manifold. It may just have to be cleaned. An ordinary can of carb cleaner should do the trick if the pintle valve inside is grunged up.

If it ran beautiful I don't see why you installed CPS. ??? 

The CPS and CAS should only be replaced if the car is stalling or shorting out. I just changed the CAS on my 95 Talon but only because it was cutting off like I turned the key off. 

If the only thing you did was change the CPS then it's not lined up right. Every car is different but the CPS usually has to be aligned.

check for minor vacuum leak and map sensor,pcv,egr valve

check the vacuum hose

I have a 1994 Cadillac Eldorado and every time i start it the car has rough Idle and the Idle fluctuate's. I also can feel it in the gas pedal when the car is doing this I tried replacing the throttle body sensor but it still does it I also was told it was the Idle error sensor. So instead of spending the unecessary money again I thought I would go online and see if anyone could help me with this problem.

Could be several things; MAF ( Mass air Flow) sensor, (Yes you should have one), could be fuel pump on the rail or the filter next to it, could be electronic idle controler, clogged injectors, ect ect, a Volvo dealer can do some simple checks of the actual components and tell you, but have someone else fix it!