Hey Gang,

Well, my LS made the trip from CT to TX with no trouble at all. I was able to find work within 4 days of arriving, now working full time in the Beaumont area.

Now that I am not traversing huge hills and whatnot, my mileage is the best it's ever been, having gotten nearly 150 miles from a 1/4 tank of gas:-) The truck is running really well, but a day or 2 ago, I noticed the idle getting rough. Now it is all kinds of stumbly at idle. Not to the point where I can see it in the tach, but I can certainly feel it.

I searched the forums but wasn't able to find much pertaining to my vehicle model.

I am guessing a vacuum leak, but have no way to check it, as I have no tools or anything.

Anyone have any suggestions on what it might be, and a good place to take it that wont fleece me?

As always, thank you in advance for any advice/suggestions.

<img src="/forums/images/graemlins/cheers.gif" alt="" /> <img src="/forums/images/graemlins/cheers.gif" alt="" /> <img src="/forums/images/graemlins/cheers.gif" alt="" /> <img src="/forums/images/graemlins/cheers.gif" alt="" />

Might be the IAC motor. Should be able to find lots of posts on that if you do a search. It's a little motor that goes into the throttle body and allows a controlled amount of air in while you're at idle. It can get gunked up or just wear out to the point that you'll eventually stall at every stoplight. You can pull it out and wipe it with a dry rag but don't spray anything on it. Could also just be a dirty throttle body. Pull off the air tube and have a look. Even a small amount of gunk around the edges of the throttle plate can cause idle problems.

Thanks for the reply, Wiggy <img src="/forums/images/graemlins/patriot.gif" alt="" />

I cleaned the throttle body per your suggestion, but it did not solve the rough idle, so I guess it's on to the IAC next. Will search for previous posts and see if I can get it done myself.

Thanks again <img src="/forums/images/graemlins/cheers.gif" alt="" />

There's a test procedure to check if the ISC/IAC is good or bad in the FSM. You'll need a multimeter and more specifically an ohmmeter.

This is the exact same problem I had on my 90 LS. First pull the ECU under the right hand dash and look to make sure it is not cooked (upper right hand corner of the circuit board)you will be able to see it. If it is burned then you need to get a new one or have it repaired. The next thing is to replace the IAC (idle air control) 25 bucks or so. The IAC can burn up the ECU so make sure it is replaced quickly. If you replace the IAC and the ECU is burned the car will still not run correctly. Good luck!
1. ECU check
2. Replace IAC (25$ and 5 mins)

Thanks off roader and DuCal for the advice. Unfortunately my ecu is cooked. I went ahead a replaced the IAC anyway, so I should be all set once I replace the ecu.

Next question is, anyone know where to get a new one cheaply? I have no other means of transport down here in TX, so I can't send this one out for repair unless I can replace it. I will repair it regardless so I have a spare in case of future issues.

Thanks again guys. I only wish I had known earlier so that I might have caught it before it fried my ecu:-(

For a used one try car-part.com or your local pull it yourself parts yard.

New one cheap? <img src="/forums/images/graemlins/lol.gif" alt="" /> <img src="/forums/images/graemlins/wink.gif" alt="" /> Seriously, I doubt you'll find a new one cheap.

Or try here.

The very nice and knowledgeable gentleman at avproecm spent a good 10 minutes talking to me. He swears up and down that he has never seen, or worked on, a Mitsubishi MD306933 ECU. He says they simply do not go bad, ever. He wouldn't even agree to look at mine. Just told me to troubleshoot.

I am looking at one on ebay, will buy it then send this one to him so he can see a bad one for himself.

Which brings up some good questions...

Is there visible damage on your ECU? How did you determine it's bad? <img src="/forums/images/graemlins/confused.gif" alt="" />