High idle when warm. Coolant temp sensor?
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Freshman User
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High idle when warm. Coolant temp sensor?
Hey guys I have another thread asking about fuel issues. I think I solved that problem and I’ll finish that thread tomorrow after I pull the bed and verify. I have an 89 f150 that’s idling high after warmup only I have replaced the intake manifold gasket, the map sensor, idle air control(fixed high idle after startup), and 02 sensor. I don’t see any issue with the vacuum line, replace the brake booster because that actually had a vacuum leak. I tested the tps at closed throttle and it reads right about .9 volts. I took a Mitty vac to the egr and it holds vacuum and works as far as I can tell. After initial start Up it idles around 1000-1100 then after a minute drops to about 600-750. After about 10 minutes or after driving down the road when I stop and park it it will idle at 1200-1500. It settles around 1500. I read on some other site (now I can’t find it) that the coolant sensor may be bad. The chiltons manual is no help but does anyone know how to proper test the temp sensor on the front of the engine to the pcm? Is there anything else I can check that could be the issue? As far as I can tell I don’t have a vacuum leak.
Cross-Country
Joined: Jul 2020
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Since we're throwing parts at it, make sure you get the sensor with 2 prongs. There's two sensors on these engines and only one sends info to the eec. You could check to see if your idle air control is fouled up as well (Not sure if speed density has these). If you want to eliminate egr as an issue, you could block that off with a plugged fender washer. Keep us posted.
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Freshman User
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Since we're throwing parts at it, make sure you get the sensor with 2 prongs. There's two sensors on these engines and only one sends info to the eec. You could check to see if your idle air control is fouled up as well (Not sure if speed density has these). If you want to eliminate egr as an issue, you could block that off with a plugged fender washer. Keep us posted.
Logistics Pro
Joined: Dec 2003
Posts: 3,777
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From: Foothills of NC
I have the resistance readings at different temps on my laptop. I will try to post it up around noon tomorrow.
When you get to warm high idle, try unplugging the temp sensor and see if your idle drops. Mine will.
If you have a 4.9, it's the sensor that's in the pipe coming off the water pump, that connects to the heater hose at the front passenger side of the valve cover.
When you get to warm high idle, try unplugging the temp sensor and see if your idle drops. Mine will.
If you have a 4.9, it's the sensor that's in the pipe coming off the water pump, that connects to the heater hose at the front passenger side of the valve cover.
Junior User
Joined: Oct 2020
Posts: 63
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From: Texas
if the control valve fixed the high idle after startups check to see if you have engine codes for running too lean or if your simply getting too much air to the combustion chamber. take a quick look around the intake and intake houses for large gaps, holes, or anything that would let too much air in. also check to see if your filter is clean and not damaged.
Last edited by rexf; Dec 20, 2020 at 11:07 PM. Reason: typo
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Freshman User
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I have the resistance readings at different temps on my laptop. I will try to post it up around noon tomorrow.
When you get to warm high idle, try unplugging the temp sensor and see if your idle drops. Mine will.
If you have a 4.9, it's the sensor that's in the pipe coming off the water pump, that connects to the heater hose at the front passenger side of the valve cover.
When you get to warm high idle, try unplugging the temp sensor and see if your idle drops. Mine will.
If you have a 4.9, it's the sensor that's in the pipe coming off the water pump, that connects to the heater hose at the front passenger side of the valve cover.
Logistics Pro
Joined: Dec 2003
Posts: 3,777
Likes: 863
From: Foothills of NC
Here's what I have for coolant temp sensor:
Fuel Injection Technical Library » Engine Coolant Temperature Sensor (ECT)
Here is a chart for intake air sensor:
http://www.fuelinjectedford.com/page29.html
Fuel Injection Technical Library » Engine Coolant Temperature Sensor (ECT)
Here is a chart for intake air sensor:
http://www.fuelinjectedford.com/page29.html
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Freshman User
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Thank you all. I’m m not seeing anything out of the normal with the sensor. Buddy of mine sprayed carb cleaner over the intake manifold like I’ve tried in the past and he actually got a result. So I’m going to pull the intake manifold off, again. Try a different gasket with some permatex and hopefully that solves it. It only does it when warm som I’m thinking the heat expansion is making a vacuum leak. Why is it whenever I spray the areas I get no result but when someone else does they get it the first try hahaha.
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Freshman User
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Welp
Well I messed up. I figured that maybe I needed to tighten the intake manifold stud to try to fix the leak and I ended up snapping one. Does anyone know the correct replacement for the upper intake manifold studs. Google isn’t much help.
Junior User
Joined: Oct 2020
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From: Texas
im not sure of the exact size and width but im sure if you went to a local junkyard and found a vehicle with the same engine you could get one of that and they might not even charge you. also i think you should loosen all the bolts again and re-torque them in the proper steps (if any) and good specs
Senior User
Joined: Dec 2018
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I Second the junk yard recommendation. Put a new gasket in and use a torque wrench. They don't need much torque.
Mi
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