Idle surge in a 1990 fwd laser

[Rklock]

Okay so I just got my rebuilt ecu in from motoguys garage off ebay and now I idle surge and my idle at start up and in neutral is a little higher than with my old one. Do these ecu's need to relearn? I messed with the idle screw too that didnt do much of anything. its set low as it is. With my old one I idled at 1000rpm with the clutch in and or in neutral with no surge. Once i put the cluch in now it goes to about 1700 then slowly works its way to about 1200 surges a bit to 1400 then goes to 1000. and stays there fine.

Any help is appreciated. thanks.

 

[SBR Joe]

Its just your IAC. You have the coolant lines running to the TB still correct?


Joe
SBR

 

[Rklock]

Honestly i have no idea. I noticed a slight leak on my thermostat housing, but I dont over heat. Could that be part of the problem? And what is iac?

 

[SBR Joe]

Honestly i have no idea. I noticed a slight leak on my thermostat housing, but I dont over heat. Could that be part of the problem? And what is iac?

Well theres a coolant line going to the throttle body coming off the back of the t stat housing, and the return going to the back part of the water pipe. If theyre hooked up (which they probably are i assume) then its your IAC.

And your IAC is the black sensor on the lower back side of your throttle body. I hate the 90 throttle bodies because i usually block off the whole FIAV/IAC part to eliminate them acting up...you cannot on the 90's. In youre case youre better off just finding a new IAC if you can. Also if the BISS screw is too far out it will cause surge problems, or if teh O ring is completely angel dusted.


Joe
SBR

 

[DSM1G90]

After I also my ECU from Motoguys, I also had slight surges (I was idling dead on at 750 before my ECU died, but after the changeout then it would settle down at 900 to 1000 when warm), but I had to redo the timing by retarding the timing down a degree or two for the time being to eliminate the slight idle surges knowing that the system couldn't find that "sweet spot" to have a good idle for it was "hunting" to find that "sweet spot".

Now, I'm back on at 750 but still with the slight timing retard.

Oh, and for record's sake: I have no BISS screw. Just a plug is covering that hole. Works great and not gonna worry about it.

-DSM

 

[Rklock]

After I also my ECU from Motoguys, I also had slight surges (I was idling dead on at 750 before my ECU died, but after the changeout then it would settle down at 900 to 1000 when warm), but I had to redo the timing by retarding the timing down a degree or two for the time being to eliminate the slight idle surges knowing that the system couldn't find that "sweet spot" to have a good idle for it was "hunting" to find that "sweet spot".

Now, I'm back on at 750 but still with the slight timing retard.

Oh, and for record's sake: I have no BISS screw. Just a plug is covering that hole. Works great and not gonna worry about it.

-DSM

okay ill see what happens. im going to clean up the throttle body first

 

[Rklock]

Well I talked to my buddy who put the car together and he said we shouldn't need to do that since we cleaned the t/b when we put it all back together. (Like 7,000 miles ago) It did it when we first got it running too, we turned the biss screw and it was fine up untill when I put in the new ecu.

 

[Rklock]

Okay guys help is needed. It still surges, a little more now. It used to stop after a few surges in neutral, now it keeps on going. And I seem to chug some times then go right into boost. what the hell is that? I checked my coil, and what do you know a wire was loose. Fixed that and it still does it every once in a while. Please help.

Thanks

 

[DSM1G90]

I call it a bad IAC unit then if everything else is in order and time. Do a search on IAC units and how to diagnois problems if it is the IAC that is acting up. For when I did my ECU (you sure you got the right ECU model-a MD 128625 for a 90 FWD Turbo Federal?), I never had this problem after I did my install.

Do a check on that ECU and make sure that all of the plugs going into that thing are seated correctly and tight. You could have one plug that isn't seated all the way.

Good luck-DSM

 

[aaschneid]

i have a 91 and had the same problem i have tried to clean the entire throtle body and that didnt do it and also replaced the iac when i got the computer and that didnt do it either but if u go to moto guys gardge web site u can call in cause that is one of the main issues they have and u can send it back as long as it is still under warenty

 

[AWD_FIEND]

Okay guys help is needed. It still surges, a little more now. It used to stop after a few surges in neutral, now it keeps on going. And I seem to chug some times then go right into boost. what the hell is that? I checked my coil, and what do you know a wire was loose. Fixed that and it still does it every once in a while. Please help.

Thanks

You've already been assisted with your question, its the IAC (idle air control). Cleaning the throttle body has nothing to do with whether or not a major sensor has failed on your car. First do a search for "bad IAC" and get informed, then change your IAC before it fries your ECU again.

 

[AWD_FIEND]

This should get you started.

http://www.dsmtuners.com/forums/newbie-forum/347832-what-happened-my-ecu.html

 

[Ahnubus_29]

Yeah like AWD said its your IAC and you need to replace it quick before it burns up your new ecu.

 

[Rklock]

Alright thanks guys! where the hell is it located? (ISC)

 

[Jets303]

Alright thanks guys! where the hell is it located? (ISC)

Come on man, ## question was answered in the third post.

 

[ilco187]

After I also my ECU from Motoguys, I also had slight surges (I was idling dead on at 750 before my ECU died, but after the changeout then it would settle down at 900 to 1000 when warm), but I had to redo the timing by retarding the timing down a degree or two for the time being to eliminate the slight idle surges knowing that the system couldn't find that "sweet spot" to have a good idle for it was "hunting" to find that "sweet spot".

Now, I'm back on at 750 but still with the slight timing retard.

Oh, and for record's sake: I have no BISS screw. Just a plug is covering that hole. Works great and not gonna worry about it.

-DSM

im just curious to know if you have no biss screw and just the plug, how under boost are you not shooting it out the throttle body, and how is you car idling, that screw is needed i thought to balance out the air or something.

and i dont have idle surge in dead of winter i can start my dsm it will idle 1000rpm right off the bat, and in 80 degrees plus weather still idle 1000rpm right off first start hot or cold i love it, i fixed that high idle problem.