diagnosing high idle

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NWMO
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Re: diagnosing high idle

Post by NWMO »

I'd suspect a mechanical issue with the throttle plate/linkages instead of a vacuum leak with the rpm that high. Sort of like the fast idle cam is always stuck on.
The FSM is available here (if you haven't found it yet). Pages FU19-23 are where I would start. The choke valve (butterfly) on top needs to open for low idle. It sounds like it is staying closed.

Chris
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dirklc
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My tercel:: 1984 Tercel 4WD SR5
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Re: diagnosing high idle

Post by dirklc »

Thank you all for the advice. We will double-check the throttle plate and we will walk through all the vac hose routing. Agree 100% with the suggestion to diagnose before I start throwing parts at it. I'll keep you posted - hopefully I can get to the culprit!
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dlb
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Re: diagnosing high idle

Post by dlb »

Just thought of some more possibilities -- could be a damaged gasket at the base of the carb, or a loose or cracked intake manifold.
luketcommandeur
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Re: diagnosing high idle

Post by luketcommandeur »

Hi all, this is Dirk's son. Fast forward from when we last posted... I replaced the alternator which got it running really well, however when we took it on a spin around the block we noticed it stalled at idle. Then in the driveway we would start it and it would run until it got warm and then die, and then as time passed the amount of time where he would stay running would decrease until we could only turn it over and have it run for a few seconds before dying. So I replaced the egr valve which was completely blocked with black gunk, swapped all the diaphrams that weren't already swapped when the carb was rebuilt, replaced the fuel filter and the TVSV. Still nothing, I replaced the last diaphram just now and started it right up (super cold might I add) and it only ran for 5 or so seconds before dying. So my questions are 1) where to now? Dizzy/ spark plugs? 2) since the egr valve was so clogged up could other parts in the exhaust/ emissions system be similarly clogged causing the problem? 3) What is this float referenced in other forums? it sounds like another T4 member was having similar problems and that's what many people suggested.
Also a few other things to note, we did the timing belt a few months ago, the fuel pump is new, the carb has been rebuilt, I can't hear any vac leaks (the majority of the vac hose is new anyways) thanks for any suggestions I really appreciate it, I've been itching to finally drive this bad boy for a while now but am pretty stumped at the moment.
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dlb
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Re: diagnosing high idle

Post by dlb »

Welcome to the forum.

I wouldn't replace any more parts until you narrow down the cause of the high idle. Even the clogged EGR wouldn't cause the symptoms you are describing. It's possible there is carbon buildup elsewhere in the engine but again, that wouldn't cause these symptoms.

It's good that you replaced all the vac hoses but have you double checked that all of them are going to the right places?

The fuel level sight glass is located on the front of the carb. Remove the air filter housing and you will see it but you will probably need to give it a cleaning to actually see the fuel level through it. Make sure the car is on level ground when checking the carb fuel level. The fuel level should be between the upper and lower points on the sight glass. If it looks good, start the engine and watch the fuel level to see if it drops or rises when the engine dies. Very important though, there is a big vacuum hose that goes to the underside of the air filter housing, this hose must be plugged or the engine won't run.
luketcommandeur
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Re: diagnosing high idle

Post by luketcommandeur »

For right now the idle problem is fixed. When it was running it ran at just above 1k rpm which I’d say is pretty decent. Now it won’t run for more than 5 seconds
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Petros
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Re: diagnosing high idle

Post by Petros »

you might try a few simple tests to see if it fuel system or spark system related:

start and run it, (air cleaner off, and the big vac line from the base of the carb capped off) and than when it dies, spray starter fluid down the carb and see if it runs. sometimes you can keep it running with successive puffs of stater spray (careful when you do this not to draw a back fire flame out the carb, use short puffs only).

If it keeps running on puffs of starter spray, it is likely a fuel starvation problem (leaky fuel line, marginal fuel pump, partly blocked fuel filter). sometimes you can have a pin hole leak in the fuel line up stream of the fuel pump and it sucks air into the system rather than enough fuel to run it, but there will be no obvious leak since the section of fuel line between the tank and the fuel pump is a suction line.

If it does not run when you do this, might either be flooded or it has a weak component in the distributor (coil, igniter, bad contact), that works when it is cold, but as it heats up will short out. you can check for spark by clamping a spark plug wire contact so it is 1/4" from the metal part of the engine and crank it, you should see a strong bluish spark that makes an audible "snap, snap, snap". if you get little or no spark, or it is mostly weak and yellow, likely the problem is in the distributor.

If it is flooding, you should see it in the float sight glass as too full, or you might have a leaky AAP allowing fuel to get sucked into the intake manifold (pull off the vac line to it and see if it is wet with fuel, if so, the diaphragm is leaky).

Sometimes if it is running too lean you can make it stay running by putting your hand on the intake horn of the carb, cutting off some of the airflow to make it more rich. that is a simple "old school" test for it running too lean. that usually means inadequate fuel supply, or vac leak somewhere making it too lean (carb, manifiold gaskets, or one of the many vac lines). mis-routed vac lines can cause that too, it can act like a vac leak. so it might be good to do a quick check of the routing and condition of all the rubber and metal vac lines.

stay with it, once you learn how the system works you should be able to narrow it down, and than correct the problem. usually the fix is fairly simple, it is finding the problem that causes the frustrations.

good luck.
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SirFoxx
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Re: diagnosing high idle

Post by SirFoxx »

are you missing the hot air line between the exhaust manifold and the air cleaner?
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NWMO
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Re: diagnosing high idle

Post by NWMO »

Welcome Luke,

As Peter shared,
If it keeps running on puffs of starter spray, it is likely a fuel starvation problem (leaky fuel line, marginal fuel pump, partly blocked fuel filter). sometimes you can have a pin hole leak in the fuel line up stream of the fuel pump and it sucks air into the system rather than enough fuel to run it, but there will be no obvious leak since the section of fuel line between the tank and the fuel pump is a suction line.
I would certainly check fuel delivery, either a clogged filter or restricted line from the tank or rust/crap in the tank may be causing problems. If you're comfortable with your skills, you can "hang" a temp fuel supply from your open hood and feed it directly to the front of the carb. If that keeps the engine running and sounding good, you can narrow things down from there.
Psalm 37:4 "Delight yourself in the Lord and he will give you the desires of your heart"

In remembrance of my friend ARCHINSTL:

T4WD augury?
"Oh, do not ask, 'What is it?' Let us go and make our visit."
T.S. Eliot - "The Love Song of J. Alfred Prufrock"

"Now and then we had a hope that, if we lived and were good, God would permit us to be pirates."
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Re: diagnosing high idle

Post by xirdneh »

I have had several carbs with the butterfly hanging up. It gets worn out on one side . If you disconnect throttle cable and start the engine and work throttle gently letting it back down to idle. If idle is high see if a light push down on linkage brings it to lower idle. If so it could be the butterfly hanging up. I add another spring to pull downward.
If you look down throat of carb you can see if there is a flat spot on butterfly. If i remember correctly its usually on forward side

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