High idle, no codes after new transmission.

T

Timjtitus

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2000 3.4 4x4 5 speed

Swapped in a new transmission over the span of a few months. Ended up taking off a section of exhaust and replacing the gaskets to make room. Added some sea foam to the tank since it sat for a while. Truck started up with an idle around 1000, not the normal higher idle at start up. Once warm it settles at or around 1500. I’ve driven it on the highway for a few days, have reset the ecu and nothing has changed. No issues prior to the transmission swap. Fresh gas is in it now.
 
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That's strange that it's not setting any codes. I would suspect a vacuum leak somewhere, but I would also expect to get a lean code too. Does the warm idle stay high if you disconnect the accelerator cable and cruise control cables?
 
Bad Luck said:
That's strange that it's not setting any codes. I would suspect a vacuum leak somewhere, but I would also expect to get a lean code too. Does the warm idle stay high if you disconnect the accelerator cable and cruise control cables?
Click to expand...


And try and force the throttle plate closed more.

Remove and clean your IAC is another step to take.


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Bad Luck said:
That's strange that it's not setting any codes. I would suspect a vacuum leak somewhere, but I would also expect to get a lean code too. Does the warm idle stay high if you disconnect the accelerator cable and cruise control cables?
Click to expand...

Removed throttle and cruise control, idle remains high
 
Make sure your throttle cable is routed correctly. When I put my CC module back in place I forgot to snap the throttle cable back in its little clamp. That was enough to have an idle at 2k when I usually had an idle of 700. This made no codes.
 
Nothing about the transmission makes the engine idle up or down. Something else was bumped or loosened that's affecting it now. I also suspect something wrong with the cable or the throttle valve.
 
We’ll cleaning the throttle body and iac did not fix the problem. I couldn’t find any alligator clips so I didn’t test the iac while it was out.
 
Worked the valve and cleaned some more. Was able to get it to open and shut with power. Put everything back together and still have a 1500 idle. Gonna spray for vacuum leaks next.
 
Timjtitus said:
Worked the valve and cleaned some more. Was able to get it to open and shut with power. Put everything back together and still have a 1500 idle. Gonna spray for vacuum leaks next.
Click to expand...


Take it for a drive and let it try and relearn the new IAC position now that it’s working.


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After more driving I’ve finally got the idle bellow 1000. No vacuum leaks detected. I’ll get post again after my long drive
 
Typical “automatic up to temp idle rpm” is 750rpm in park and neutral and 600rpm in gear with foot on the brake.


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Timjtitus said:
After more driving I’ve finally got the idle bellow 1000. No vacuum leaks detected. I’ll get post again after my long drive
Click to expand...

Per the FSM, idle speed is to be 750 RPM +/- 50 RPM. You're pretty close. It should continue to adjust as you drive as when I reset my idle it usually takes about 3 days of driving of 2 or more stops to fully re-learn all idle conditions. It looks at data such as air temperature and engine coolant temperature so if one of those is different it has to re-learn the idle speed for that specific data set.
 
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