1st DSM, What bolt is this on throttle body ?!

[SpinningAll4]

Hey guys, this is my first post here but have been lurking for years. After searching high and low for a decent 1g AWD in one piece, I finally got one. I knew the previous owner so I knew alot about the car when buying it. Anyways on to the point. He said he suspected a boost leak, so I got my boost leak kit out and pressured up the system. I only found one leak, and that was on a silver bolt on the front of the throttle body. I have included a picture to indicate what I'm saying. I tried to find countless pictures of a 1g throttle body to see what it is but I just can't. With Irene here all weekend I had no chance to get a Hayne's or Chilton book. Can anybody identify this bolt that failed the boost leak test miserably ? Thanks, Joe

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[Dhan]

Talk about Jerry-rigging

It is your base idle speed screw (BISS). After you ground the ecu, it allows you to adjust the base idle up or down in rpms when you're car is idling and under no load.

I suggest getting an OE replacement from Mitsu. That is a major vac leak and idle surge cause.

Here's some info http://www.vfaq.com/mods/BISS-1G.html

 

[Bud92gsx]

Here are the actual part numbers..So you can call mitsubishi and get the right part..

Idle screw o ring 07788s
Idle screw 07708s
Cap 07793

 

[1991 awd talon]

So i just read the link u just provided kreez. and is there one of these on the 420A motor? im having trouble with it not idling correctly. could this be the cause? me and my dad have tried a lot to figure it out. even did a compression test on the cylinders and they were all fine.

 

[agentorange313]

I hope its not a bolt and was screwed into the biss screw threads.

If it was, I would look into using sealant around the new biss screw, and getting the cap for it.

 

[TSi Kid]

Hahaha sketch.

DSMs, keeping it classy since 1989.

 

[Dhan]

I hope its not a bolt and was screwed into the biss screw threads

This is a good point. After getting the parts Bud listed, be 100% certain that the hole down into the TB is sealed. You'll have endless a/f mixture problems otherwise.

So i just read the link u just provided kreez. and is there one of these on the 420A motor? im having trouble with it not idling correctly. could this be the cause? me and my dad have tried a lot to figure it out. even did a compression test on the cylinders and they were all fine.

The 420a motor doesn't have an idle screw to adjust like the 4g63. Idle is controlled by the ECU and the IAC. I would start by checking for vac leaks. And I mean really go over that thing with a fine tooth comb.
You can also pull the IAC unit off and clean it. I know that's cured some 420a issues for some folks. While you're messing with the IAC, check the throttle body and clean it with some carb cleaner.
You can test the IAC to see if it's working properly too. I don't know the exact procedure for testing it, because I don't have a 420a shop manual. I'm sure a quick search would produce results though.

GL

 

[1991 awd talon]

its a/t but thank you maybe thats what ill do today?

edit; sorry didnt see the "shop" before manual

 

[Lofty]

You probably need a new throttle body.

I'm speaking from experience.

 

[TSi Kid]

Run a boost leak test to see if it leaks first before replacing anything major.

 

[SpinningAll4]

Wow I ran to go grab my check and came back to great responses ! Thanks guys I will certainly buy all OEM Mitsu parts for this. I am hoping that the previous idiot who did this didn't damage the threads that badly and the throttle body is still usable. Trust me if it's anything I have learned about DSM's its to have another commuter car to have also so downtime on a new throttle body wouldn't be a big deal, but still costs money and time. Thanks for all your help this will be my next fix on this car so I will post pictures when I'm done.

 

[XiKeiyaZI]

Talk about Jerry-rigging

It is your base idle speed screw (BISS). After you ground the ecu, it allows you to adjust the base idle up or down in rpms when you're car is idling and under no load.

I suggest getting an OE replacement from Mitsu. That is a major vac leak and idle surge cause.

Here's some info 1G BISS Adjustment

Absolutely correct. Thread should have stopped here.

Should be able to replace the jerry-rigged with the correct BISS screw. Make sure to use a little sealant on the threads, not much.. just a very thin film.

Worst comes to worst, either retap the hole or get a rebuilt throttle body and resolve a few potential issues at the same time.

 

[Bud92gsx]

Like keiya said worst comes to worst get a new tb..Snowboarder714 sells rebuilt and bead blasted ones..So there like brand new..

 

[92AWDHX40]

Wow thats a first find a used one i sold my spare, on ebay, and classifieds or snowboarder.

 

[agentorange313]

Absolutely correct. Thread should have stopped here.

Should be able to replace the jerry-rigged with the correct BISS screw. Make sure to use a little sealant on the threads, not much.. just a very thin film.

Worst comes to worst, either retap the hole or get a rebuilt throttle body and resolve a few potential issues at the same time.

If he retaps the biss screw hole, do you know what size the thread pitch is?

 

[92gsxbafaro]

okay you need to get a new biss screw i actually have one in the mail for me now its like 12 bucks after shipping...

here is site for proper adjustment
1G BISS Adjustment

 

[SpinningAll4]

thanks guys, again it's greatly appreciated. I ordered the parts through my dealer and have to find time to head up 40 minutes to pick them up. Most likely on my day off tomorrow I'll be doing this.

 

[spritian]

Don't get the cap, it'll eventually just blow out and get lost haha

 

[Boostinsideways]

The cap keeps that plastic screw from drying out and cracking and shit. The cap is rather important. I usually put a small dab of thread sealer on the cap before reinstalling it just so it doesn't disappear.