1991 fj80 idle issue. Not like the rest! (3 Viewers)

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yodanut91

yodanut91

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Sep 22, 2014
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So I did a carbon clean to the old 3fe and now every time I cycle the key the idle goes up slowly 100rpm per cycle and stops at 1200rpm. Removed cleaned and tested IAC according to the fsm. Iac works fine. No intake leaks. If I plug the inlet to the iac it idles perfectly. If I reset the ecm it idles fine for 2-3 key cycles but after that it does it again and slowly creeps up to 1200 and sits there. Either ECM or the IAC? I am stumped. I tested the TPS and it tested out ok, set the adjustment as per FSM. Help me!
 
I have no suggestions but will give you a sympathy bump. Good luck!
 
Carbon clean? Intake removal and carbon build up is removed... pretty common issue if the EGR leaks like mine did. And it idled fine before hand. I checked everything for leaks and found none. It idles fine when the ecm is reset. But slowly the IAC opens and bumps up the idle after each key cycle. I was thinking IAC. But I don't know. I removed the ecm last night and inspected it for bent/damaged pins. Put it all back together and so far it is still good.....it is almost like the ecm is being told to bump the idle up.
 
Is there a re learn procedure for the IAC? I could not find one.
 
The ECU wouldn't develop a bent pin by removing the intake manifold. I think it's a safe bet to say that something was not reassembled correctly.
The IAC valve is a 4 position stepper motor that gets pushed by the ECU. If the ECU keeps pushing it, then the ECU is getting the incorrect signal from the something.
 
That is what I was thinking, right now it is running fine after ecm removal and re installation. Possibly a bad connection on a pin? Not sure.... I will wait and see. I cleaned all the grounds and checked continuity to ground from the harness and the bolt it goes to. Checked the simple stuff first. I think the IAC might be to blame but I am not sure. I was going to throw a new one at it and see.
 
i did take everything back apart ad checked my work, i found nothing wrong. it came apart easy and went back together easy too. day 2 with the ecm R+R and still idling fine......not to sure what to think about this!
 
yodanut91 said:
i did take everything back apart ad checked my work, i found nothing wrong. it came apart easy and went back together easy too. day 2 with the ecm R+R and still idling fine......not to sure what to think about this!
Click to expand...
There was something I read 100 years ago before Ih8mud was born on the old 80sCool email list. It referenced a high idle on a 1FZ-FE and the fix was some sort of a spacer on the ISC valve. My brain is old and crusty and sometimes full of dirt, so I may not be remembering this correctly.
I believe that the ISC needs an OEM gasket to be positioned correctly in the throttle body. Did you use a new OEM gasket or re-use the old one?
IIRC there are also torque specifications for the screws, but I could be wrong.
 
I am not a mechanic by any means but doesn't the ECU have to "relearn" when you make changes sometimes. I've heard of guys disconnecting the negative battery terminal, driving for 15 minutes, and repeating 4-5 times. Someone correct me if I'm wrong. Once again, I am not a mechanic or expert at all.
 
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The intake kit did not come with one so I used a little sealant.... I will order the correct gasket right away. Thankyou!
 
LS1FJ40 said:
I am not a mechanic by any means but doesn't the ECU have to "relearn" when you make changes sometimes. I've heard of guys disconnecting the negative battery terminal, driving for 15 minutes, and repeating 4-5 times. Someone correct me if I'm wrong. Once again, I am not a mechanic or expert at all.
Click to expand...
You bring up a very valid point, but the OP has already done this.
Removing the 15 amp EFI fuse in the under hood fuse box for a few minutes is all that's required and is less invasive than removing battery terminals. This clears the memory of the ECU and allows it to relearn the basemaps of all sensors. I do this anytime I do any work under the hood.
 
I've heard guys on here say to do it 4-5 times and that it takes 15 minutes of driving to reset everything. No experience with it myself. I've only had one CEL in 22 years (knock on wood) and that was my igniter going bad. Could it be different on the fancy FZJ's compared to our tractors? ;)
 
LS1FJ40 said:
I've heard guys on here say to do it 4-5 times and that it takes 15 minutes of driving to reset everything. No experience with it myself. I've only had one CEL in 22 years (knock on wood) and that was my igniter going bad. Could it be different on the fancy FZJ's compared to our tractors? ;)
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LOL. This stuff is all 1985 technology. Doing it once or doing it 10 times makes no difference. Once the memory is cleared, the memory is cleared. It doesn't get "more cleared" :)
It also takes more than 15 minutes of driving for the ECU to get a correct base map on everything, depending on how/where you're driving.
 
jonheld said:
There was something I read 100 years ago before Ih8mud was born on the old 80sCool email list. It referenced a high idle on a 1FZ-FE and the fix was some sort of a spacer on the ISC valve. My brain is old and crusty and sometimes full of dirt, so I may not be remembering this correctly.
Click to expand...

I think this is what Jon was referring to: http://lcool.org/technical/80_series/fast_idle/fast_idle.html

I tried this many moons ago but didn't get the desired results but I may not have had the proper sized o-rings.
 
Thanks guys! I ordered the gasket and it is on its way from japan :)
 
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