Ok well my RS with an automatic trans is my DD most of the time and it has 200k miles on it. It has had this problem for awhile, but it seemed a lot worse today. When I'm at a stoplight the car starts to shake when idling and the RPMs drop to about 800 or so, sometimes a lot lower. It shakes pretty bad, but not horribly. Now also to fix this I usually put it into neutral to stop it. I did that today and I got idle surge, it would go back and froth from 1500 and 1000. Now it only idle surges when it rains (which really baffles me). The car also has a number of CEL codes. I fixed a few of them but haven't cleared them yet. I'm probably going to have a diagnostic run on it at some point, but for the time being does anyone have any idea on what it could be? I believe its a faulty sensor of some sort that is getting wet.

Your first step should be this, Keydance. Do the keydance so we can narrow down the codes, then start testing & inspecting. It works well for this sort of thing.

Keydance Link How To.

http://2gnt.com/index.php?d=PCM_Error_Codes

Jeff.

Originally posted by 740TurboBrick

"Dsms run on Gasoline, DSMers run on Alcohol...Id bring a tank to refuel the DSMers..."

200k miles? Probably a number of things to check. First I'd go over all vacuum lines. This picture will help you trace em out. See if any are cracked/worn.



Also look over the EGR if you do not have it removed. There is a metal pipe roughly 1" OD that runs from the back of the intake manifold and the front/side of the head. There is a main wiring harness that runs near that pipe that gets hot. It is possible for the wires to come in contact with the pipe and melt some of them.

Reference: http://www.2gnt.com/index.php?d=EGR

You could also pull the throttle body and open the butterfly plate and clean it out. Also pull the IAC and clean it as well. There's sure to be some carbon buildup in there. You could also test for a faulty IAC which could give you the shaky idle problems you describe. Should output 0-4.2v, anything over that and it starts freaking out typically.

http://www.2gnt.com/index.php?d=IAC
http://www.2gnt.com/index.php?d=Sensor_locations

It also wouldn't hurt to read up on the MFI system for our vehicle.

http://www.2gnt.com/index.php?d=Description_of_the_Stock_MFI_System

Also with the high mileage, you may want to do a compression test to see where your motor stands. Depending on your goals/plans for the vehicle, a rebuild may be in order.

http://www.2gnt.com/index.php?d=Engine_Compression_test

I know I've pretty much just bombarded you with a crapload of information, but take your time, read up on it, and you'll be on your way in no time. Remember we're here to help.

I contributed to the Wiki.

Well thank you for all the help guys. I know it needs a rebuild, but I don't plan on keeping it much longer since I have two GS-Ts now. I have already done the key dance and fixed a lot of the problems in accordance with the codes awhile back. Compression is a little low in cylinder 2 if I remember correctly (I did it a while back too). That is really about it. I will definitely try your suggestions though, other than this and the oil leak its had since I got it, it still runs fine.