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No fast idle at startup


Terry

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1987
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Ford Ranger
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Manual
Looked around here and did not find. My new to me 87 4 x 4, manual shift 2.9 ranger. I have been building on this truck for a while. I bought it for 300 with a blown head gasket. I have a dead 86 2 x 4, automatic 2.9 ext cab that I am robbing all the parts off of for the 87. I did an "old school" valve job "hand lapped" and put these heads on my new truck. This issue was there before the valve/ head gasket job. The truck does not high idle when in "open loop", start up. Once it wams up enough it will idle. My question is, when it is in open loop does the IAC control the cold start idle?
 


freedom5

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1987
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Automatic
Looked around here and did not find. My new to me 87 4 x 4, manual shift 2.9 ranger. I have been building on this truck for a while. I bought it for 300 with a blown head gasket. I have a dead 86 2 x 4, automatic 2.9 ext cab that I am robbing all the parts off of for the 87. I did an "old school" valve job "hand lapped" and put these heads on my new truck. This issue was there before the valve/ head gasket job. The truck does not high idle when in "open loop", start up. Once it wams up enough it will idle. My question is, when it is in open loop does the IAC control the cold start idle?
The engine also uses an Engine Coolant Sensor to control the IAC. It's the three wire sensor ( not the two wire that goes to the temp gage). It's kind of hard to get to. I ended up removing the thermostat housing to replace mine.
 

raggadie

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I agree with the above poster, I would check the same thing. Do you have any issues with smells while driving the truck when it is first started up?

I had the same issue, but mine was running rich all the time. After I replaced it, start up ran much better, and it no longer ran rich after it heated up.

After you test it, and it doesn't fix the problem, let us know. From that point we might be able to go further. Also, are there any other problems that you are having that might help us determine what the root cause is?
 

kimcrwbr1

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maplevalley WA
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ford
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It could be a plugged IAC valve or dirty throttle body? The TPS also controls the IAC it should fully close when you open the throttle butterfly so run it abut 2000 rpms after it has warmed up disconnect the IAC valve and let off the throttle the engine should stall or barely run. Plug it back in and it should idle normally.
 

freedom5

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I also have found that if I turn on the A/C right after start up and before the engine warms up a bit it will sometimes die. I am assuming that the computer tries to set the IAC based on the A/C being on. If I wait just a few minutes after starting and the high idle comes down to normal turning on the A/C doesn't affect it.
 

RonD

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Looked around here and did not find. My new to me 87 4 x 4, manual shift 2.9 ranger. I have been building on this truck for a while. I bought it for 300 with a blown head gasket. I have a dead 86 2 x 4, automatic 2.9 ext cab that I am robbing all the parts off of for the 87. I did an "old school" valve job "hand lapped" and put these heads on my new truck. This issue was there before the valve/ head gasket job. The truck does not high idle when in "open loop", start up. Once it wams up enough it will idle. My question is, when it is in open loop does the IAC control the cold start idle?
The IAC(idle air control) valve controls the idle at all times, cold or warm.
Fuel injected engines do not have "jets" like a carb, and idle needs to be constantly adjusted, so a "controlled vacuum leak" was used, the IAC valve.

Computer gets RPM of engine from CKP(crank position) sensor OR in your model year the TFI distributor sensor.
Computer has preset idle RPM values that are based on engine temperature.

Engine temp is read from the ECT(engine coolant temp) sensor, this is a TWO wire sensor.
Dash board gauge uses a ONE wire Sender.

Computer sends ECT sensor 5volts, and then reads the voltage coming back thru sensor, if engine is cold(60degF) computer will get back 3volts, as engine warms up voltage coming back will go down, under 1 volt is warmed up.
So on cold start RPM may be 1,100, then drop to 900 after a minute or two then drop to 750 after 5 minutes(warmed up).

IAC valve reads like it is not working at all in your case, because on cold or warm starts RPMs should go up to 1,500 then drop quickly to preset values, this is the computer open IAC valve all the way then closing it.

Often pulling it off and cleaning will get it working again.
 

Tedybear

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My credo
Failing is easy. Everyone can do it.
Unplug the coolant temp sensor and start the truck.

If the truck starts up and goes to about 2k RPM and holds---(Yes your CEL will come on doing this) Then shut the engine off and plug the sensor back in. Restart. If the truck dies? My money is on the coolant temp sensor.

I say this because my 89' with the 2.9 started like total &hit, coughing and spitting...rough...low engine vacuum.. Removed the plug to the sensor--and upon restarting the engine pegged 2k RPM and held it.

It's a test that costs zero to preform.

S-
 

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