ISC idle issue

[tpetrucci33]

Ok so I'm having some trouble due to a bad isc. I recently purchased one in good working condition (resistance tested out ok). I popped it in and still had the idle surge. I pulled the Ecu, and find that the drivers are burnt...

I put in another Ecu (rebuilt) with the good isc... And still have the issue!! I tested the connector and am getting 12v from 2 pins.. I'm at a loss here guys. Any thoughts or ideas?

Thanks in advance

 

[stars]

When you installed the new I.S.C did you cycle the key from on to off several times? It has to reset itself otherwise it does not know when to step it out or in. You may have to disconnect the battery for several minutes and then cycle the key from on to off several times. I have seen this method suggested several times over the years and is the easiest to do first.

 

[tpetrucci33]

Ok I haven't done the on/off cycling. I'll disconnect my battery and let it sit for awhile, reconnect it, then try the on/off cycling.

Thanks for the tip.

No luck with disconnecting the battery or cycling on/off position. I'm letting the car run for about 10 minutes or so to see if the issue goes away.

Any other ideas?

 

[stars]

Checking it while running with a scan tool to make sure the I.S.C is stepping in or out properly. Retrieve any codes if any in the E.C.U. Make sure your idle close switch on the T.B. is in the proper position and working with the throttle open and closed. Check the connector to the idle close switch as well. I have had an I.S.C that would show Ohms to proper specs but, it did not work properly (especially used ones). I finally ended up buying a new one and that solved my idle surge.

 

[tpetrucci33]

Hmm what's the purpose of the throttle body switches? (Open and closed)

 

[stars]

Very good question. When the throttle plate is closed such as when you first start it up or come to a stop you let your foot off of the accelerator, the throttle plate is closed and the I.S.C adjust in and out or step in or out to adjust the amount of air to keep the car idling. If the I.S.C does not allow the right amount of air thru the T.B., the engine will experience a stall and die. When the throttle plate is open the I.S.C is no longer needed and the I.S.C shuts off until you let your foot off of the throttle. This repeats itself over and over throughout your drive.

Now, what commonly occurs is that the I.S.C will try to adjust the amount it steps in or out to allow just enough air flow so the car does not stall out and die when it senses that the throttle plate is in the closed position. Since your car is experiencing the idle up and down from about 750 R.P.M's to 1200 and there about, it is very annoying. The I.S.C is trying to adjust and it is having a difficult time trying to adjust and allow the proper amount of air to flow past the Throttle Body while the engine is at idle. This is a very common problem, just about everyone will have this happen to them if they are running the stock setup. Think of the I.S.C as an air metering device, if the Throttle plate is entirely closed the engine will lack air flow and will stall, the I.S.C meters just the right amount of air to compensate for the throttle plate closure, and allow enough air to enter the intake to keep the engine running.

I would assume your closed switch is working because the I.S.C is trying to adjust, hence that is why the R.P.M's vary up and down which can be a bad thing when you put your car into gear at over 1000 R.P.M's so it is important to get this problem fixed.

 

[tpetrucci33]

Well to sum it all up, does that throttle body switch activate the isc when the throttle body is closed? Or does that switch not play a factor in regards to how the isc functions?

 

[stars]

Yes it does, it completes the circuit and the E.C.U receives the signal that the circuit has grounded. MACH V has a good description of the switches function, 1G DSM Idle Speed Switch Obviously they leave out some symptoms that can occur when the switch either malfunctions or out of adjustment it can cause the E.C.U to try to prematurely regulate the I.S.C. by thinking your at idle and thus trying to engage the I.S.C. at the wrong time? I have often wondered about that exact issue but, have never had any proof that it can occur. Soon as the E.C.U receives the signal that the I.S.C has grounded it activates the I.S.C. to either step in our out to adjust the amount of air flow into the T.B. at idle. Remember that the I.S.C. needs a base line to know where step #0 is so you may have to repeat the cycling of the key on and off several times in order to get the I.S.C. into the correct position. You may have to repeat the process a few times in a row so do not be discouraged if you do not get a result the first time around. You may have to test drive during each key cycle to get the I.S.C. to understand which step it needs to be in. Remember to test drive once you have made adjustments. Depending on the mileage of your 1G and year it was made you may just as well get a new I.S.C. and save your used one for a backup. If you can afford to own an BMW ( I work on these for a living b.t.w) you can afford to get a new I.S.C.. Just be glad Mitsubishi is not like B.M.W.'s you might as well have 2 wives if that were the case, they both are high maintenance and expensive..=). to own.