Weird idle changing between D and R

[oboc]

Well I've done lots of reading over the past 1-2+ months about a weird running / idling issue with my 1996 V6 VS Commodore.
I have replaced (with new genuine parts):
- Both oxygen sensors
- TPS
- IAC valve
- Spark plugs
- Ignition leads
- Fuel filter
- Air filter
- Swapped coil packs with a set from wreckers

While the car is running a lot better than it was before I replaced the above (I replaced in stages to try to isolate issue...new oxygen sensors made the most benefit - one of of them was rooted; passenger side FWIW).
The car still doesn't seem to be running as nice and economically as it did 6+ months ago...the most apparently problem now is, once the car is warm, when I change from D (drive) to R (reverse) or vice versa, the car will almost stall as it engages the new gear. It still isn't getting the fuel economy it used to.
It is looking like an electrical issue now, rather than mechanical??

My brother has suggested the "Idle up" might be stuffed...I have consulted my Gregory's workshop manual, and google, and can find no reference to such a component...can anyone shed light on this "idle up"? or perhaps suggest something else to look at as I am over it and am trying to avoid taking it to a mechanic (or auto electrician) as money is tight as I'd rather get the satisfaction in fixing it myself...

Thanks and sorry for the wall-of-text...

 

[adam10_1990]

Where does your idle sit when in park? and i could only think torque converter or auto clutch plates in the gearbox itself

 

[vrsprspt]

Checked for any vaccum leaks, cracked or perished hoses?

 

[Not_An_Abba_Fan]

One thing to try is to reset the TPS, disconnect the battery for 10 seconds, reconnect and start the car in Park. Rev to just over 2000 rpm for 10 seconds, then turn car off. See if that helps.

 

[KrisG]

Mine did this a while ago, it would almost feel like stalling for a few seconds as you described. Turns out I was low on transmission fluid from a slow trans cooling hose leak. I topped up and it was back to normal again. I'd suggest checking your trans fluid level as per the user manual.

Also a transmission service would be beneficial if it hasn't had one in a while, it's fairly straight forward and cheap to do yourself too.

 

[FstStig]

Make sure your MAF isn't clogged up with crap, try giving it a clean with some MAF Cleaner. There might be a Dirty injector as well.