Wierd slight idle surge?

[IIv SHaDoW vII]

Ok...the problem is on my 98 gs auto (420a).

The car drives and idles normal, but sometimes while slowing down and while almost completely at a stop I hear the idle change as if it was just downshifting (rise slightly then change back to normal). Ok seems normal right? Well it also does it in reverse and neutral. To be as specific as possible.. Yesterday I was backing down the driveway without hitting the accelerator while the car was in neutral, I let it roll down the hill and once I get into the street the idle went up...and down.. When I accelerate its normal and when I say the idle rises and falls...it never falls below normal, it seems to only take place when the car is idling or slightly rolling. It does this everytime I drive it. It doesnt cause any abnormal engine/tranny problems or anything.. truthfully I have no idea if its even normal since I havent dealt with this kind of engine before.. I have tried to diagnose it myself by seeing if it was related to pressing the brakes or turning the wheel.. I dont think the brakes affect it but when I turn the wheel it seems to be a slight bit more noticable. I do have the vaccuum line from the TB going to the egr solenoid unplugged and NOT plugged.. Should I plug that and see if the problem goes away? Any ideas.. or am I just an idiot?

 

[Talesin]

Yes, you should plug that line. Idle surge is usually caused by a vacuum leak (aka: intake leak past the throttle body) and if the EGR vac line is tapped to the inside of the TB, that'll create a pretty notable leak.

Yes, you should never just leave a vacuum line hanging and un-plugged. Take off the vac line entirely (assuming it's just a line from the TB to the EGR with no split-offs in the middle) and cap off the nipple with a vacuum cap. They're cheap.

 

[IIv SHaDoW vII]

Thanks, I just got this car about 3 months ago, so ya know... previous owners..