High throttle at start up?
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Senior Member
Joined: Oct 2004
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From: Florida
High throttle at start up?
Simple question: When I start my truck uo after having not been run for a while, the throttle seems to hang high longer than it use to. It hangs around 1000 rpm's for like 5 minutes before it finally settles down to the 750 mark. Anyone have any suggestions.
Senior Member
Joined: Jan 2005
Posts: 130
Likes: 0
From: Dublin, OH
The IAC is responsible for controlling idle. It is normally commanded higher or lower as the actual RPM is lower or higher than the desired RPM. There are three choices:
1) The desired RPM is 1000 for several minutes
2) The IAC isn't responding to the lowered (750) desired RPM
3) A vacuum leak/dirty throttle is keeping the idle high
Testing (1). When it is at 1000 RPM, turn the air on and turn the wheel stop to stop to load the engine. If it initially dips and then returns to 1000 as you turn the wheel with the AC on and flares and settles back to 1000 as you stop turning and turn off the A/C, then the desired RPM is 1000. The most likely reason would be a bad ECT (coolant temperature sensor) or a bad IAT (intake air temperature sensor) making it think it's so cold that it needs to high idle longer. This would also make it run rich longer.
Testing (2). When cold, wait 1 minute so the idle should have slowed down and tap the IAC firmly with the handle of a screwdriver. If the RPMs drop then, it is dirty and should probably be replaced.
Testing (3). If neither above test, look for vacuum hoses unplugged, use a stethoscope or fuel hose to 'hear' vacuum leaks, use propane or carb cleaner, or use a smoke machine to see if there are vacuum leaks.
1) The desired RPM is 1000 for several minutes
2) The IAC isn't responding to the lowered (750) desired RPM
3) A vacuum leak/dirty throttle is keeping the idle high
Testing (1). When it is at 1000 RPM, turn the air on and turn the wheel stop to stop to load the engine. If it initially dips and then returns to 1000 as you turn the wheel with the AC on and flares and settles back to 1000 as you stop turning and turn off the A/C, then the desired RPM is 1000. The most likely reason would be a bad ECT (coolant temperature sensor) or a bad IAT (intake air temperature sensor) making it think it's so cold that it needs to high idle longer. This would also make it run rich longer.
Testing (2). When cold, wait 1 minute so the idle should have slowed down and tap the IAC firmly with the handle of a screwdriver. If the RPMs drop then, it is dirty and should probably be replaced.
Testing (3). If neither above test, look for vacuum hoses unplugged, use a stethoscope or fuel hose to 'hear' vacuum leaks, use propane or carb cleaner, or use a smoke machine to see if there are vacuum leaks.