Rebuilding is not difficult. If you prefer to have someone rebuild it for you:

http://throttlebodys.com

@snowborder714 May be able to help u out also.

Jumpy rhythmic idle is usually your IAC valve (or ISC same thing) which are notoriously bad and can fry your ecu if not replaced. If you replace it and still have the problem pull the ecu and check the drivers. The longer you go with an fuc*ed up idle the higher probability of ecu damage (no biggie, you can find a used 97 ecu for about $50)

Replace your IAC with the better black one if you still have the tan top. I get them here:

https://m.ebay.com/itm/Mitsubishi-3000GT-IAC-91-99-IDLE-AIR-CONTROLLER-Control-Valve-Stealth-MD628053/162836317417?fits=Model:3000GT&epid=1224952746&hash=item25e9cd04e9:g:aCQAAOSwCMtaTtO5

You can't beat lifetime guarantee on a used part! I've ordered 3 so far and theyre all good

The main purpose of a TB rebuild is to thoroughly clean the TB and replace the little shaft seals and the BISS o ring. Most people bypass the FIAV when they do this. This eliminates the coolant lines to the TB which aren't necessary. Personally I've had super filthy leaky TBs which really showed minimal difference when cleaned. The tan IAC/ISC is a troublemaker on DSMs and there's a reason they're replaced even if they test ok.

With the above posts, I refreshed the throttle body with new shaft seals again and a FIAV bypass. My idle has never been more consistent.

When it had the FIAV and coolant lines hooked up it was notorious for idle changes +- wouldn’t hold a steady rpm. I live in Washington and it’s like 30-65 degree days from now till June-ish. My car starts now, idles at 1300+-100 and then once it gets settled at operating temp it’s right around 750+-rpm.

thanks for the help guys. appreciate you sharing your knowledge and experience. ill get in there tomorrow and check it out, but what i'm hearing is rebuild the throttle body by cleaning it and applying new shaft seals and o ring, add an FIAV bypass, and then replace the IAC sensor. Right?
@PlanZero will that iac sensor work even though it says 3000GT and I have the eclipse gst? any other recommendations for where i can get oem parts?

2gmitsueclipse said:

Rebuilding is not difficult. If you prefer to have someone rebuild it for you:

http://throttlebodys.com

Click to expand...

As a noobie would you recommend i do this? seems like there's plenty of how to's on the web that i could use as a guide and save a couple hundred bucks. or would it be smarter to pay a veteran?

Yes it's the same IAC.
There's a good you tube video on how to do it, just search DSM throttle body rebuild.
The BISS o ring is a #6(double check) from home depot.
The shaft seals are about $15 from extreme psi (order through eBay to save shipping)
Use a power screwdriver and proper size bit with pressure when removing the plate screws. You'll strip them if not.
You can bypass the FIAV for free by popping out the freeze plug on the TB, take needle nose pliers and screw the FIAV plug all the way in. Replace the freeze plug using some rtv. Or you can buy the bypass plate for $10. Loop the coolant line in the car.
Clean the shit out of the whole TB.
It's fairly simple if you're even remotely mechanically inclined, the hardest part is winding the spring properly, which is easy if you mark it good with a sharpie before removal.
Or just pay someone to rebuild and stick a better IAC (don't lose the O ring) on there. Use new TB gaskets. Dsms are notorious for shitty idle, it's best to familiarize yourself with all parts of the TB and sensors so you can troubleshoot. You are going to learn how to do everything now that your buddy is gone. Get a Haynes manual or download the FSM. You will quickly go broke if you start paying someone to do repairs on a 21 year old turbocharged car.
You can often find 2g TBs for under $30. Its always good to have a backup, and you can practice and take your time if the DSM is your DD

I recently replaced my IAC valve with the tan one and a month later the car randomly started surging so I can attest to the fact that those things are indeed finicky.

Samuel Larsen said:

As a noobie would you recommend i do this? seems like there's plenty of how to's on the web that i could use as a guide and save a couple hundred bucks. or would it be smarter to pay a veteran?

Click to expand...

I could only recommend you make that determination. If you have the tools necessary and gumption to try it out, go for it. I have replaced shaft seals on a Throttle body twice, and have used throttlebodys' services twice. While I typically prefer to do my own work, I do prefer the like-new condition of a Throttle body without the hassle of doing it myself. Some benefits of having the service done if you choose:

• You don't need to worry about the fasteners you will likely strip upon disassembly.
• The parts are all cleaned/bead-blasted to look new.
• If you send in the unit with sensors, they will all be tested. He usually has spares if sensors need replaced for an additional charge.

To my knowledge, there are no longer any supporting vendors whom offer this service.

FYI the brown IAC saved my ass in my 98gst auto. The black box ECU seemed to like brown IAC, I had tried 3 different black top ones, including an ac Delco brand from my 96gst and all failed to respond to signal. Brown one off the junkyard car worked immediately. The initial high idle kick from the brown IAC also cured my trans pump issues when cold (black box ecu's do not suffer from ECU driver failures)

I tried and failed to rebuild my throttle body. Don't mess with it. It's a crappy can of worms, I wish I would have just paid the $140 to have some one else rebuild it rather than having to fine tune it like a carburator.

You could also upgrade while you're at it. I got a 1g TB off eBay for $25, rebuilt it and ported my IM to gasket match. Combined with a non cruise cable (rock auto-$14) Immediately noticed throttle response improvements. Highly recommend.