tapping pedal when starting cold??
#1
12-20-2006, 09:45 AM
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#2
12-20-2006, 10:29 AM
Two Problems come to mind. Defective TPS ( Throttle Position Sensor) or dirty/defective IAC (Idle Air Control) valve. Remove and clean the IAC valve. Do you have access to a Multimeter to test the voltage of the TPS? Do you know where the IAC is? If not I need to know which engine you have to show pics of where it is.
JMC
JMC
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12-20-2006, 10:37 AM
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Thank you for quick response. 4.6 is the motor I have. Just my luck though. Since I started this tread I found out that I may have blown a head gasket. So I guess that is my main concearn now. I am new to the site and enjoying already. Even though I just received some bad news about the motor.
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12-20-2006, 08:21 PM
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#5
12-20-2006, 11:33 PM
Assuming there is no major faults like your indicating, you should be able to put the key in the ignition switch and crank the engine to start without ever touching the throttle.
The system is set up that way by intent.
You would need to know how it does it to be able to check out the areas that are involved. The TPS isn't a big factor in cold starts since it never moves at that time unless the throttle is moved.
The IAC, IAT and ECT are the major players in cold starting.
Why: As you turn the ignition switch to run before start, the PCM looks at the cold values of the ECT and IAT. This sets the fuel injection rich and fully opens the IAC so the idle goes high. This is how the PCM knows it is to be a cold start.
Then as both the OX sensors come up to temp, a PCM internal timer brings the idle speed down slowly and according to how cold the ambient temp outside is, the OX sesnors take over fuel control.
Anything that does not operate correctly will interfere with this action.
By opening the throttle, you are adding extra air only and almost no fuel of any amount as compaired to the PCM's control cold fueling, at that time.
You can see the areas that can affect the total result.
Sorry it's not easy but thats how it's done.
The system is set up that way by intent.
You would need to know how it does it to be able to check out the areas that are involved. The TPS isn't a big factor in cold starts since it never moves at that time unless the throttle is moved.
The IAC, IAT and ECT are the major players in cold starting.
Why: As you turn the ignition switch to run before start, the PCM looks at the cold values of the ECT and IAT. This sets the fuel injection rich and fully opens the IAC so the idle goes high. This is how the PCM knows it is to be a cold start.
Then as both the OX sensors come up to temp, a PCM internal timer brings the idle speed down slowly and according to how cold the ambient temp outside is, the OX sesnors take over fuel control.
Anything that does not operate correctly will interfere with this action.
By opening the throttle, you are adding extra air only and almost no fuel of any amount as compaired to the PCM's control cold fueling, at that time.
You can see the areas that can affect the total result.
Sorry it's not easy but thats how it's done.