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, Thu, 2 Oct 2014 03:25:31
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Chris,
for the crankshaft to be running (or spinning, whatever) the following conditions must be met:
- the engine bits must be solid and not damaged (i.e. cracked piston leads to leaky combustion chamber when all the gases are leaking thru instead of pushing the piston down; or an increased friction - either from missing lubrication from the oiling system or from mechanical stress happened due to heat stress happened due to defective cooling system - will give the engine an extra load which in extreme case will stop the crankshaft)
- in a case of gasoline engine with mechanical throttle drive the fuel management system must supply the proper amount of fuel (and the fuel must be of proper type with certain combustion value and evaporability)
- the ignition system must ignite the air-fuel mixture right at the proper time
- the exhaust system must take the whole charge from the combustion chamber and quickly take it away (i.e. a clogged exhaust will give you the same throttling as the stock throttle in the intake)
Since the issue appears to get resolved somehow, then it isn't something mechanical nor it is the exhaust (a clogged TWC usually doesn't get clean on its own). So it's either something from the fuel system or from the ignition system. You didn't say anything about rain or cold mornings so it's hardly the ignition wires. Moreover, ignition system defects usually give you a noticeable detonation, lack of power/overheating or uneven farts in most engine running modes - which you didn't mention either - so I'd strike the ignition system out. So we have the fuel system only. Let have a closer look...
You didn't say anything about drivability or the changengine indicator so it isn't something like general system fault or emissions-related issue. According to your description the engine was having the only issue which is running when the accelerator pedal was depressed. In this mode the engine is breathing thru the IAC valve only which is driven by the EFI ECU. So most probably this valve wasn't opening enough to provide the engine with sufficient amount of air. This happens if:
- the IAC is internally mechanically or electrically damaged (i.e. stuck or burnt out; the latter should not be your case since it later cured on its own - burnt devices do not do that)
- there isn't enough current to drive IAC (ECU FET faulty, bad IAC wiring, damaged IAC connector, bad engine power ground connection)
- the EFI ECU is fooled and is running using incorrect data (this can come from almost everything: from bad signal ground thru intake (aka vacuum) leaks to defective ECU RAM/EEPROM)
As a sidenote I'd add another interesting (and quite real!) possible reason for this faulty: worn wiring in the engine wiring loom which got old and lost its flexibility. An idling engine is producing some certain vibrations in a certain frequency spectrum. So if the wiring is no longer flexible then it can not withstand vibration stress and can give you a whole lot of possible troubles at resonant frequency. Lower RPMs mean lower frequencies and higher wave lengths so it may be worth inspecting wiring loom especially having a closer look at its lengthy segments.
Oh, damn, I wrote a book!..
Zig
posted by 5.18.176...
, Fri, 3 Oct 2014 11:34:19, Wed, 1 Oct 2014 13:47:36
, Wed, 1 Oct 2014 15:22:58, Thu, 2 Oct 2014 03:24:17, Thu, 2 Oct 2014 03:25:31, Thu, 2 Oct 2014 08:14:00, Wed, 1 Oct 2014 10:10:59, Wed, 1 Oct 2014 10:27:56, Wed, 1 Oct 2014 10:54:58
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