92 3FE High Idle & Rev Surge

[ocinataS]

Brilliant! I never even considered that.
Might want to address the rest of the coolant system.

Yes, a coolant flush is next on the list. I’m reading up on that to figure out the best way. Also want to dislodge passages where coolant may have clogged up. Maybe a cleaning agent of some sort might help.

Thanks for all the suggestions.

 

[ocinataS]

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.

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

Man... sorry to hear about your 3FE. Someone totaled a car I’ve had for 10 years and 167k miles last week while it was parked outside my house and it sucks to give it up after taking care of it for so long. My 92 runs strong and has plenty of life left in her. Thanks for those tips!

 

[ocinataS]

Might want to address the rest of the coolant system.

I’m going over the FSM before the flush. Are my coolant hoses wrong? The FSM shows a loop from thermostat, to ISC, to Intake (upper connection), and back from Intake (lower connection) to thermostat.

But my LC Goes from the thermostat, to ISC, to Intake (LOWER connection), and then back from Intake (UPPER connection) to thermostat - red arrows.

 

[jonheld]

Are my coolant hoses wrong?

Without having a 3FE in front of me, I can't tell.
It's difficult to see, but the hoses in your picture appear to be original.

 

[Rush]

Here's what the intake that came off my 3FE looks like:

I agree with Jon, your hoses look original.

 

[ocinataS]

Here's what the intake that came off my 3FE looks like:
View attachment 2370478
I agree with Jon, your hoses look original.

Mine look the same as yours. Thanks

 

[Rush]

Mine look the same as yours. Thanks

Thank you, dude. I'm gonna double check my ISC's coolant passages before I fire up the new motor.

As far as the flush goes:
1. I would do a backflush of the heater cores, to get the casting sand and aluminum/rust flakes out. The lines for this are the two pipes running along the head, to the firewall. I did a manual backflush (cheap harbor freight fluid transfer pump, with a gentle hand and two buckets) and I got more sand than I expected from a 245k mile truck. Flush both directions, but backward first.
2. I bought a bottle of coolant flush at O'Reilly's for ten bucks. I'll run it after initial break in.

 

[ocinataS]

Thank you, dude. I'm gonna double check my ISC's coolant passages before I fire up the new motor.

As far as the flush goes:
1. I would do a backflush of the heater cores, to get the casting sand and aluminum/rust flakes out. The lines for this are the two pipes running along the head, to the firewall. I did a manual backflush (cheap harbor freight fluid transfer pump, with a gentle hand and two buckets) and I got more sand than I expected from a 245k mile truck. Flush both directions, but backward first.
2. I bought a bottle of coolant flush at O'Reilly's for ten bucks. I'll run it after initial break in.

Yeah, double check that. Mine had a pretty good blockage (couldn't blow through). I think from sitting for periods of time before I bough it.

I appreciate the tips. I'll do that. Seems like everyone has a different way of doing it. Some more extensive than others.

I put in a bottle of Prestone Flush & Cleaner yesterday and will drive it around a bit before I do the flush. I bought 3 cases of distilled water and have coolant coming in this week.

 

[proteolytic]

Trying to make sense of this issue. Sounds like the coolant system in general needs to be flushed/maintenanced and possibly the temperature sensor checked per FSM. Coolant into the ISC, as I understand it, is to prevent the valve from freezing in cold climates (mine came completely bypassed when I purchased it). Issue sounds more likely is that the truck does not have a good flow in the cooling system which can throw off the temperature sensor and could affect idle (as well as gas mileage).

 

[ocinataS]

Coolant into the ISC, as I understand it, is to prevent the valve from freezing in cold climates.

I've seen people say this in different forums, but I haven't found anything convincing to confirm coolant flows here to prevent freezing. As the coolant warms, the ISC lets less air bypass the throttle body.

 

[proteolytic]

Looking at the FSM diagram and the actual ISC there doesn't look to be any temperature sensors in that part of the ISC let alone any other part of the ISC that would affect its operation at different temperatures. Yes, sorry, late response - working on my ISC for other reasons and came across this thread again. Looks like the coolant can warm up the metal part of the ISC but has no input into the actual activation of the mechanical side.

 

[91FJ80FD]

I have a crazy idle problem when in drive, it drops below 400 rpm's for a sec. then jumps back up and acks like its starving for fuel? I have de-smogged the engine 3FE, now looking for answers?

 

[Thor45]

@ocinataS did you replace ISC gasket when you removed it.

 

[ocinataS]

@ocinataS did you replace ISC gasket when you removed it.

It’s been so long, I don’t remember specifics on this. I’ve never reused a gasket on the LC, so I’m pretty sure I put in a new one.

Truck’s still running great, BTW.

 

[ocinataS]

@91FJ80FD sorry, I haven’t come across an issue like that

 

[jonheld]

I have a crazy idle problem when in drive, it drops below 400 rpm's for a sec. then jumps back up and acks like its starving for fuel? I have de-smogged the engine 3FE, now looking for answers?

Possibly torn intake plenum.