92 3FE High Idle & Rev Surge (1 Viewer)

Joined
Apr 25, 2020
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Modesto, CA
Hoping someone’s come across this issue.

New to me 80. At startup, idles at 1600 RPMs. P & N is 1600. Any gear idle is 1000 RPMs.

Another issue is that at startup, when I press the brake to put it in D, the RPMs drop to 900 and surge up to 1200 repeatedly. This stops when I go into D, then it holds steady at 1000. This won’t happen though if I put it back in P and press the brake. But it’ll happen again if I turn the ignition off and start it up again. Every time I start and press brake, the surging happens until I go to gear.

The high idle problem has been going on since after I bought the truck 2 months ago. I didn’t take note of what the idle was when I bought it because I didn’t know what was normal. I learned what idle should be while doing baselining tasks. Among other things, I’ve replaced worn vacuum hoses, cleaned throttle body, intake plenum. Vacuum hoses seem to be ok and the tubes from the air filter aren’t cracked.

The surging happens for a few days then will not happen for a week or two.

I replaced the O2 sensors today since I would intermittently get 25/26 CELs.

Throttle wires aren’t stuck. Ran the FSM diagnostic on the TPS and it checked out OK.

At a loss. Any ideas?
 

YMT

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Mar 20, 2017
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El Portal, CA
Check the large hoses on your intake for any tears. Mine did the same, and my hoses were bad.

Also wouldn't hurt to check all your rubber under the hood and make sure they're all good.

Have you baselined your rig yet? Assuming not, replacing hoses is almost a necessity.
 
Joined
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If you're idle speed is 1600 rpm, then your throttle is open.
The 3FE is a fuel injected tractor motor. The mechanical adjustments have to be correct first.
Proper adjustment procedure of the throttle cable is to have someone slowly depress the accelerator pedal fully while you watch the throttle plate. Once the pedal is on the "floor" the throttle plate should just be touching the endstop. When released, there should be some slack in the cable.

Other than the cable adjustment, you should also make certain that the mechanical movement of the throttle is smooth from endstop to endstop. If a chunk of carbon or other foreign matter is preventing the plate from closing, then it's going to screw with the idle.
 
Joined
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Modesto, CA
If you're idle speed is 1600 rpm, then your throttle is open.
The 3FE is a fuel injected tractor motor. The mechanical adjustments have to be correct first.
Proper adjustment procedure of the throttle cable is to have someone slowly depress the accelerator pedal fully while you watch the throttle plate. Once the pedal is on the "floor" the throttle plate should just be touching the endstop. When released, there should be some slack in the cable.

Other than the cable adjustment, you should also make certain that the mechanical movement of the throttle is smooth from endstop to endstop. If a chunk of carbon or other foreign matter is preventing the plate from closing, then it's going to screw with the idle.
Thanks, Jon. I cleaned the TB and plenum when I purchased, but I took it off again to see if anything was blocking closure. Mechanical adjustments were good. Opens fully when pedal is bottomed out, and closes fully when released. Stop screw isn’t preventing closure with no clearance. There’s a little slack in cables when pedal is released.

Resistance at TPS terminals check out per manual.

i adjusted the golden screw a half turn from full clockwise and rpm at P/N is down to 1200 from 1600.

There seems to be a problem with the Idle Speed Control (ISC) Valve, but I’d like to confirm I’m testing it correctly. When applying + battery to B1 and B2, and grounding S1 - S4 / S4 - S1, I hear a slight click with each grounding, but the valve doesn’t move up/down. It should move up and down, right?

I’ve attached a picture of the valve and FSM page with the test procedure. That is the position it’s been in since I pulled it out of the plenum.

Could the ISC Valve be the problem?

2E8E9E55-7E4F-4EDF-AF7F-39AC0CB5A8AC.jpeg


29CEBE6F-ED32-46C2-BCC8-0DA3A7A853C8.jpeg
 
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I see now that the ISC doesn’t cycle up/down with just one S1-S4-S1 sequence. Mine does move 1mm or less with each grounding. So the ISC seems to work.
 
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Modesto, CA
FIXED

Got the idle down to normal. Not sure which of these made the difference, but for anyone in the same spot, I did the following:

Removed and cleaned ISC/IAC valve. Diagnosed as instructed in FSM and confirmed it functioned ok.

Recalibrated TPS per FSM. It was off slightly.

Tightened kickdown cable slightly and loosened throttle cable accordingly.

Double checked stop screw and dash pot screw per FSM.

Sprayed silicone lube on dash pot spring.

EBA0913A-55D9-4485-BF02-8C114362EF3D.jpeg
 
Joined
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Good. That idle speed is a perfect 650.
Assuming all mechanicals are correct, the combination of the ECU reading the info from the TPS and bumping the stepper motor in the ISC is what controls the idle speed.
I would suggest pulling the EFI fuse and allow the ECU to relearn the sensors. This should result in a slightly higher idle speed for a few drive cycles, but will come back down to 650. There should be no other ill effects.
The "golden screw" DOES NOT set idle speed. Adjusting it will have only a temporary effect as the ECU will continue to push the ISC to make the idle speed correct.
 
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Good. That idle speed is a perfect 650.
Assuming all mechanicals are correct, the combination of the ECU reading the info from the TPS and bumping the stepper motor in the ISC is what controls the idle speed.
I would suggest pulling the EFI fuse and allow the ECU to relearn the sensors. This should result in a slightly higher idle speed for a few drive cycles, but will come back down to 650. There should be no other ill effects.
The "golden screw" DOES NOT set idle speed. Adjusting it will have only a temporary effect as the ECU will continue to push the ISC to make the idle speed correct.
I spoke too soon. RPMs soon crept back up to 1250 in P/N and 900 in gears. I've driven many cycles and about 60 miles since pulling the EFI fuse. The RPM surging is also back, but this seems to only happen after startup when the car is already fully warmed up.
 
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Northeast PA
I have the same issue with mine.. including the bouncing between 800-1200. I have not solved it yet.

I haven't looked at it much since replacing everything you've replaced.. but I have a sneaky suspicion it has something to do with a vacuum leak in the power brake system. I intent to check the vac line from the brake booster to the valve cover, the check valve, and the booster itself someday.

When my air conditioning is on, and I first start the car it will bounce ONLY after I hit the brakes. When I shift into Drive it settles out (although still high). Assuming the high idle, and the bouncing are related - that points toward the AC system, or the brakes (in my case). I'd imagine the AC ties back into the throttle in some manner to increase idle as the compressor loads. I also know the brake booster works because of vacuum.

I don't have any answers, or definitive leads.. I'm just spewing all the info that's in my head hoping it helps in some way.
 
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I have the same issue with mine.. including the bouncing between 800-1200. I have not solved it yet.

I haven't looked at it much since replacing everything you've replaced.. but I have a sneaky suspicion it has something to do with a vacuum leak in the power brake system. I intent to check the vac line from the brake booster to the valve cover, the check valve, and the booster itself someday.

When my air conditioning is on, and I first start the car it will bounce ONLY after I hit the brakes. When I shift into Drive it settles out (although still high). Assuming the high idle, and the bouncing are related - that points toward the AC system, or the brakes (in my case). I'd imagine the AC ties back into the throttle in some manner to increase idle as the compressor loads. I also know the brake booster works because of vacuum.

I don't have any answers, or definitive leads.. I'm just spewing all the info that's in my head hoping it helps in some way.
That's interesting. My AC doesn't work and I haven't really looked into it yet. PO said it worked right before I bought it, but now neither the compressor or AC dash light come on. You might be on to something between that and the brake system.
 
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I spoke too soon. RPMs soon crept back up to 1250 in P/N and 900 in gears. I've driven many cycles and about 60 miles since pulling the EFI fuse. The RPM surging is also back, but this seems to only happen after startup when the car is already fully warmed up.
When the engine is shut down, the ECU resets the ISC. You should hear 3 clicks from under the hood when this happens. It is a very distinctive sound.
If the ECU can't reset the ISC, it will remain in its last position.
I would carefully inspect the ISC wiring and make sure there is not a faulty connection.
 
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When the engine is shut down, the ECU resets the ISC. You should hear 3 clicks from under the hood when this happens. It is a very distinctive sound.
If the ECU can't reset the ISC, it will remain in its last position.
I would carefully inspect the ISC wiring and make sure there is not a faulty connection.
I'll check for a sound and wiring when I get home. Thanks.
 
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When the engine is shut down, the ECU resets the ISC. You should hear 3 clicks from under the hood when this happens. It is a very distinctive sound.
If the ECU can't reset the ISC, it will remain in its last position.
I would carefully inspect the ISC wiring and make sure there is not a faulty connection.
On shut down, the ISC makes a rattling noise followed by about 5 quick clicks. Normal?

Wiring looks to be in good shape.
 
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On shut down, the ISC makes a rattling noise followed by about 5 quick clicks. Normal?

Wiring looks to be in good shape.
I don't ever recall a "rattling noise", just the clicks as it resets.

If you are certain, and I mean ABSOLUTELY CERTAIN that:
1. The throttle cables are not sticking (pedal cable to cruise control actuator/cruise control actuator to throttle/transmission kick down cable)
2. That the cruise control actuator mechanism is not sticking
3. That the throttle cables are adjusted correctly
4. That the throttle mechanism is clear of debris
5. That the TPS has passed FSM tests and is adjusted correctly

Then it is possible that the ISC valve is failing or sticking in an open position.
The AC compressor "idle up" signal is a logic high (+12) to the ECU connector E6 pin 10 (black/white stripe). I doubt this is the issue, but it would be prudent to at least check it.
 
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Just wanted to update anyone troubleshooting this issue. My idle is fixed now and it turned out to be a simple problem - clogged coolant pipes on the ISC assembly. With no coolant getting in, the ISC would idle high as if the engine was cold. With warm coolant flowing, the valve closes and restrict air flow.
 

leonard_nemoy

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Just wanted to update anyone troubleshooting this issue. My idle is fixed now and it turned out to be a simple problem - clogged coolant pipes on the ISC assembly. With no coolant getting in, the ISC would idle high as if the engine was cold. With warm coolant flowing, the valve closes and restrict air flow.

From reading this thread I think you will have no problems keeping your rig maintained and running good. You should be able to drive that thing another 150,000 miles with no problems. I got lucky with my 3fe. She had 185,000 on the clock when I picked it up and I had very few issues to deal with. She was still running strong at 285,000ish when I totaled her last month. :frown:

Although my speedometer cable failed a few months ago and I tried everything to find a new one. They are completely unobtainable. If your ever take your dash apart you should take the entire cable assembly out and try to clean and lube it. And here is a link to a company is Aussie land that sells the discontinued sensor for the cruise control.

HALL EFFECT SENDER 12-24V 4 PULSE C6001
 

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