1991 3FE engine idle changes at start. (1 Viewer)

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I recently traded my Ford Excursion for a 1991 fj80. I am digging my new truck and have been working out the bugs. This site has been a big help. The engine runs strong and sounds good but the idle changes at almost every start. I set the golden screw so that the lowest idle is around 600 and now sometimes it will start and Idle at around 1300. I have replaced the Fuel pressure regulator and TPS. I have checked that the ISC valve and MAF work correctly; they check out per FSM. I have checked fuel pressure and vacuum and both seem normal. It is drivable but the idle is driving me nuts. Are there any 3FE gurus out there who have heard of this problem?
 
Temp sensor near thermostat has a crappy wire connection, goes bad easily. can put a new connector on it pretty easily..


PS, is your Alt wire warm ? Clean and re-attach your coil holdown cage bolts. is a major ground that goes wonky
 
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The "golden screw" sets static air intake. The ECU will push the ISC to set the idle correctly.
The setting for the screw should be no more than 3/4 turn from fully seated.
Correct idle is 650 RPM.
 
HI, I've never changed the gold screw in any of our cruisers. Set it back to what Jon said . Look for vacuum hose leaks,there are lots of old vacuum hoses . Mike
 
Every once in a while the "idle adjustment screw" or "golden screw" thread pops up.
It sets the static air intake at the throttle body at idle. It will have a TEMPORARY effect on engine idle speed, but the ECU will continue to push the ISC to make the idle correct for the conditions it sees.

Remember, 1986 technology. The mechanicals have to be correct first or the sensors will be outside of the adjustment window that the ECU can "see".

You should also remove the 15 amp EFI fuse on the left fender after any sensor replacement (or really any underhood exercise) and allow the ECU to relearn the sensors. It will also clear out any existing error codes.
 
Thank you for the replies guys. I wasn't able to work on it yesterday and I have to work today. I plan to tool around on it tomorrow. When I set the golden screw to about 3/4 or a turn from closed it can sometimes idle around 650 and sound perfect. Then I turn it off and on again (within in seconds) and the idle will be about 300 and it will konk out. So I move the screw out until it idles at 650 and it will be fine. The next day I start it and it will be at 1300. I have checked all the vacuum hoses and replaced a few. Right now I think that Morganism is on the right track; it is starting to seem like an electrical problem. I will be working on it tomorrow. Thanks again
 
This may be obvious but are you taking into account that a "cold start" even in sunny Southern California the idle is not going to start at 650 RPM? High idle is normal to warm the engine as fast as possible to reduce exhaust emissions for the first few minutes. After that then idle should be at 650.
 
Thank you to everyone who has responded so far or is about to. I was able to find the time to work on my FJ80 this morning and I have found what seems to be an electrical problem. I am using the 3FE repair manual that I found online because I don't have the FSM or Wiring diagram for the proper year (short on money right now), it has been doing me well so far. I started by disconnecting the battery terminals to be safe. Then I disconnected the computer. I looked for continuity between terminals that on feel should have continuity and quickly found something strange. Terminal E1 shows up in 3 places that found in the 3FE repair manual. It is supposed to be body ground. When I check from the diagnostic port on E1 to body I get perfect continuity. From the computer E1 port to ground I get around 1k ohm. On E1 at the MAF to body I get infinity. None of the terminals show continuity to each other. Did the wiring diagram change from the 3FE manual to FSM in 1991? I believe all the E1s should always be tied together and connected to body. Where is this ground to body?
 
I am using the 3FE repair manual that I found online because I don't have the FSM or Wiring diagram for the proper year (short on money right now), it has been doing me well so far.

Look here and download.
 
I just realized that there are differences in the wiring from the 3fE repair manual to the 1991 version of the 3FE that I have. I looked at the documents at the download section that 4ADVNTR linked and I am not finding the one that matches what is actually going on in my engine. I am transferring money to my Paypal account to send to jonheld. It looks like I will have to wait a bit to figure it out. I need accurate drawings that I can be sure are correct.
 
I got the proper documentation now (the 3fe manual and the 1991 FSM do certainly have some differences in the electrical system). At this point I am all but certain that this idle problem is something electrical. I am starting by troubleshooting the grounding system. I have already found some funky results. It might take me a bit to figure it out but I will report when I get somewhere or get stuck.
 
(the 3fe manual and the 1991 FSM do certainly have some differences in the electrical system).

Can you report on some of your findings, there? I have the FSM printed out, but not the 3FE manual (just have the digital copy), and I haven't dug into very deep to see where there are discrepancies.
 
Odds are you have a vacuum leak as jonheld mentioned above. Look for cracked intake hoses from airbox to intake manifold and check all vacuum hoses.

The 91-92 FJ80 has many differences compared to the 88-89 FJ62 3FE. Off the top of my head the ECU and the TPS are different.
 
So I found the problem (at least one of them). One of the wires that leads to the ISC valve is open circuit. This would stop the ISC from working correctly. The problem is that to get to wires that I need to inspect and work on I have to take off the air intake (looks like a pain in the butt). If I do that I am going to need a bunch of gaskets to put it back together. Anyone have any suggestions before I undertake this mission?
 
Instead of doing the correct way and taking off the intake I decided to take a shortcut and run a single wire over and around. Good news is that the idle is correct now at somewhere around 650. I am choosing to wait to take off the intake until I have to money and time to buy new injectors and all the correct gaskets and other parts so that I only do it once and do it correctly. I would have figured it out a bit quicker if I had had the correct documentation from the beginning. Thank you to everyone who replied

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