1G So much I don’t know where to start with this 1G NT

[SplayTick]

New to the forum and new to these cars. I found myself in a tight spot due to illness and losing my job and then my jeep losing its engine. I picked up a 93 Laser RS for $700. This car has mostly sat for almost 5 years. It has a lot of issues and money is tight and this is my only vehicle. I will do my best to describe everything properly.

The engine idle surges
If the MAF is plugged in the car will start but dies immediately
The transmission is in limp mode
There is an exhaust leak (undetermined location at this point)

The previous owner replaced the TPS, MAF, and ECU as well as doing a full tune up on it. I have checked the resistances on the MAF and they check ok. I have checked the voltages on the harness side of the MAF plug and they check ok. I have cleaned the ISC as checked the voltages/resistances on it and they appear to be ok as well. I went to check the BISS and it appears it is completely missing and where it goes has a bunch of dirt/grime in it and though I don’t know where I should see threads I’m not seeing any.

That’s all I have at this point as between rainy weather and my new job I just started diagnostics have been limited. Any help I can get on where to start would be much appreciated. I attached photos of where the BISS should be. Also, the previous owner did tell me they adjusted the idle but I’m not sure how they adjusted it.

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[CrackedDSM]

Circuit board repair and those schematics are waaay beyond me. I have no clue. Lol.

But, if you measure resistance between the coils on the ISC and it’s fine, you should be fine. If it was replaced previously you’ll be fine.

Good luck in repairing the board! Keep us updated either way.

 

[SplayTick]

Will do and I appreciate all the help you all have given me. Hopefully I’ll know enough soon to help others.

 

[waltah]

Is it possible that any of the issues I already addressed would have had the TCU in limp mode?

You've got two dead TCUs. They do that, and when they discover they're dead, they go to limp mode.

I have checked the IAC and it checked ok on my multimeter. Is it possible that it could appear ok and not be? I want to try this other TCU but if there is a possibility that the IAC could still be burning the TCU I don’t want to risk it and will replace that before I try this TCU.

The Idle Air Control is a motor driven needle valve with a magnetic revolution counter (to report needle valve movement) in the gear train. It's strictly an output device for the ECU, the mechanism by which the ECU controls the RPM when the throttle position switch says the throttle is closed.

The IAC could indeed be bad even though it passes multimeter tests; most commonly the needle valve breaks (many are plastic) or jams due to dirt or loss of lubricant. Rarely the motor dies -- I think they're conventional DC motors so brushes will eventually go. But I think it is impossible for this to cause trouble for the TCU.

You've made a lot of progress!

 

[SplayTick]

Now that the MAF is able to be plugged in and those codes have been cleared I have had one more code pop up. Checked it and it’s the coolant temperature sensor. I don’t know what it is about this town but just about everything for this car is between 4-7 days out on it coming in. Got one ordered but won’t be in until Tuesday next week.

You've got two dead TCUs. They do that, and when they discover they're dead, they go to limp mode.

The Idle Air Control is a motor driven needle valve with a magnetic revolution counter (to report needle valve movement) in the gear train. It's strictly an output device for the ECU, the mechanism by which the ECU controls the RPM when the throttle position switch says the throttle is closed.

The IAC could indeed be bad even though it passes multimeter tests; most commonly the needle valve breaks (many are plastic) or jams due to dirt or loss of lubricant. Rarely the motor dies -- I think they're conventional DC motors so brushes will eventually go. But I think it is impossible for this to cause trouble for the TCU.

You've made a lot of progress!

I appreciate the info. I’m looking into the toggle switches until I can get mine repaired.

I did remove the IAC the same day I tested the coils. I didn’t have any way to apply the proper voltage to it to test movement so the resistance is the only check that has been done. Since it’s only $37 online and it’s the factory one in the car right now I’m going to go ahead and order a new one when I get paid next week.

 

[Mech Addict]

I had ecm tuning give my ecu a full check and replace caps as precaution when I bought my car. Price was very reasonable, just sayin’. Not questioning your skills, but if they will work on tcu the same as ecu, hard to justify spending your time on it.

 

[streetraceboi]

Send them to ECMlink and have them reviewed and repaired. Theyre very good with pricing, as Mech mentioned. Itll save you time and a headache.

 

[SplayTick]

It’s been a bit since my last update. The car is running MUCH better now. I got a new IAC in it yesterday as well as a new coolant temperature sensor. Every now and then the idle bogs down to around 500 when in gear and it’s a little shaky but I don’t have the new BISS in yet. For some reason I’m still getting codes for the ECT sensor. The old one did check bad on the resistances and the new one checks good.

I got the TCU out yesterday as well and wired up the toggle switch shift. The post I was using on here said not to mess with the blue wire unless you want smooth shifts but it didn’t go into any more detail on that. All solenoids work and I have all gears now but I would like it to be smoother. Does anyone have any links they could give me to research more on what I need to do to the blue wire to control the line pressure?

 

[SplayTick]

Been a while since I updated anything on this. I broke my leg in June so all projects had to come to an end. I am on the upswing now. I have a TCU on the way. I’ve been driving for quite a while (minus the last two months) with toggle switches wired up for shifting which has been working pretty good. I am thinking the FIAV needs R&R because I get a high idle, around 2k, when I first start it and it slowly goes down. Once warm it idles around 650RPM. I saw a post on here months ago that led me to a kit for it but I can’t find it again. Would I be better off to R&R the FIAV or get a block off plate?