the solenoids are controlled by the vacuum switches on the right fender well. As I recall, one is is to cut off the fuel when down shifting so you do not allow unburnt fuel out the exhaust (also prevents back firing when down shifting, using the engine to slow the car.
The other one shuts off the fuel supply when the ignition is turned off to prevent run-on dieseling. If that one is closed no idle fuel will get to the engine, and it will not idle properly. Sounds like that one is the issue. Not sure if it is controlled by the ECU, I thought it was just supposed to be open when the engine is running, and closes when you turn off the ignition. So it seems it would be powered by the ignition switch. Check the wire diagram.
How to get rid of fast idle when hot?
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Petros
- Highest Ranking Member
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- My tercel:: '84 Tercel4wd w/extensive mods
- Location: Arlington WA USA
Re: How to get rid of fast idle when hot?
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)
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marlinh
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Re: How to get rid of fast idle when hot?
I have a factory wiring manual at home for an 85 (I think)that I can scan for you. At work right now. PM me a reminder and I will do that first chance I get.
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mrdance123
- Top Notch Member
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- My tercel:: 84 and 85 4wd wagons
Re: How to get rid of fast idle when hot?
Replaced the intake/exhaust gasket, problem 90% solved, idling much more stable.
My theory explaining the odd symptoms:
With a leaking intake manifold gasket,
the carburetor idle gets adjusted up to compensate and obtain normal idle speed.
When the head and manifolds heated during driving,
heat causes metals to expand, tightening things up,
reducing or eliminating the vacuum leak around the gasket, resulting in faster idle.
So it takes a while for things to cool, letting the idle fall to 'normal'.
Regarding the fuel cutoff solenoid:
I burned something out by mistake, applying 12 volts to the solenoid ground wire leading to the ECU.
Swapping in a known good ECU from another car did not resolve problem,
maybe the wiring lost it's continuity between the carb solenoid and ECU.
I cut the solenoid ground wire that led to the ECU, and grounded it directly.
Now the solenoid is always on with ignition.
But...it will never cut fuel during deceleration....it's cut only with ignition off.
Have not observed any odd behavior at deceleration. as a result.
Normally, the ECU will command solenoid fuel cutoff,
when there is sufficiently high RPM's, and the vacuum switch(es) detect high vacuum.
My theory explaining the odd symptoms:
With a leaking intake manifold gasket,
the carburetor idle gets adjusted up to compensate and obtain normal idle speed.
When the head and manifolds heated during driving,
heat causes metals to expand, tightening things up,
reducing or eliminating the vacuum leak around the gasket, resulting in faster idle.
So it takes a while for things to cool, letting the idle fall to 'normal'.
Regarding the fuel cutoff solenoid:
I burned something out by mistake, applying 12 volts to the solenoid ground wire leading to the ECU.
Swapping in a known good ECU from another car did not resolve problem,
maybe the wiring lost it's continuity between the carb solenoid and ECU.
I cut the solenoid ground wire that led to the ECU, and grounded it directly.
Now the solenoid is always on with ignition.
But...it will never cut fuel during deceleration....it's cut only with ignition off.
Have not observed any odd behavior at deceleration. as a result.
Normally, the ECU will command solenoid fuel cutoff,
when there is sufficiently high RPM's, and the vacuum switch(es) detect high vacuum.
85 T4 Speedy Blue, SR5, 270-312k, operational R12 A/C, in use.
84 T4 Curmudgeon Copper, 188-294k, my first T4 in 1990, now Dad's daily driver.
RIP - 84 T4 Foxy Blue, 256-288k, engine died 2021, sold to PNP
Sold: 86 T2 Silver, VIN ending 5847, 194k, cherry condition, now in a good home.
RIP - 83 T4 Smokin' Gold, 270k, rusted out body, parted & scrapped
RIP - 84 T4 Quicksilver SR5, 125k, blown engine no oil, had sat 10+ years, parted & scrapped.
RIP - 80 Corolla (purchased new), 0-473k, 358k original engine, rear-ended totaled in 2003.
84 T4 Curmudgeon Copper, 188-294k, my first T4 in 1990, now Dad's daily driver.
RIP - 84 T4 Foxy Blue, 256-288k, engine died 2021, sold to PNP
Sold: 86 T2 Silver, VIN ending 5847, 194k, cherry condition, now in a good home.
RIP - 83 T4 Smokin' Gold, 270k, rusted out body, parted & scrapped
RIP - 84 T4 Quicksilver SR5, 125k, blown engine no oil, had sat 10+ years, parted & scrapped.
RIP - 80 Corolla (purchased new), 0-473k, 358k original engine, rear-ended totaled in 2003.