Recently purchased 2002 35th Anniversary coupe, automatic, with 90k miles. Completely stock except for Borla Exhaust. Car ran great when I first got it, with exception of slight lifter noise from one cylinder. Just installed SLP air box lid, started it up and it would not idle above 400 to 500 RPM. Had to depress pedal just slightly to increase RPM to keep it running and leaving it at 1000 RPM and taking my foot off the pedal, it would stay running. Blip the throttle and RPM would drop back down to below 400 and barely run. Barely touch the pedal again and RPM would again go back up to around 1000 and stay there. Shut it off, checked everything under the hood to make sure I didn't leave anything unplugged and everything was OK. Noticed the small setscrew under the throttle cable cam and thought if I screwed it upward it would do the same thing as the idle adjustment screw does on a carburetor. Using an inspection mirror, I found out the setscrew is a torx and a real small one at that, and I didn't have one that small. Needing something real thin to place on top of the setscrew to increase the idle RPM, and stay in place, I found a real small plastic ziptie that was only about 1/16th inch thick. So, I wrapped it around the setscrew and the metal tab that holds it, pulled it tight and started the car. PRESTO! It runs like it did when I got it. The ziptie is still in place!
So, now my question. WTF!? Why did the idle RPM change when I changed the air box cover?

 

just changing the lid should not do anything like that. did you try running without the lid on for a second to see if there is air blockage of some kind.

 

No, but I ran across something yesterday that might explain it. When I had everything apart, I did a little cleaning of the throttle body. Didn't spray anything into it, as it really wasn't dirty, but did spray some brake cleaner on a rag and opened the throttle plate all the way open to wipe the back of it. What I read was that if the throttle plate is opened a full 90 degrees, it messes up the throttle position sensor. Didn't really think anything about it when I read it, but got me to thinking later that maybe that's what caused it.

 

if you have or have access to a scanner it will let you see what the tps is showing. it may be the computer is seeing the tps is not where it really is.

 

Don't have a scanner or access to one, but took car to friend who owns local auto repair shop. Told him about issue, he took ziptie off and car idled fine. Evidently I just didn't didn't drive car long enough after installing new air box lid for computer to learn new air/fuel parameters.
Ya learn something new every day!

 

it may also be that the tps worked its way back to where it was before.

 

Probably just CMS ! (computer magic ****)