GMC to Ford

I have recently developed an issue where the truck remains at high idle (~1000 RPM) when stopping at a light or coffee stand. It sporadically occurs under the same conditions (engine warm and stopped with the transmission in Drive). If I rev the engine, it returns to a high idle. Turning the engine off and back on will restore the idle back to normal ~600 RPM. I searched the forum without any luck. My truck has 63000 miles. Does anyone know of a possible cause? Also, I do not have any codes.

52merc

The first thing you should do is check of DTCs with a diagnostic tool.

[F2C]MaDMaXX

I'd be looking at the condition of the throttle body actually, give it a good clean and then perform the idle position reset once cleaned.

GMC to Ford

I will check for DTCs tomorrow.

GMC to Ford

I assume it is better to pull the throttle body for cleaning and install a new o-ring.

[F2C]MaDMaXX

Yup, but i wouldn't think you'd need a new o-ring, so long as the old one looks good.

Flamingtaco

Clean the o-ring and channel it sits in. If the o-ring still sticks slightly out of the channel, it will seal with no issues.

Kathy Sullivan

Did you ever figure out what was causing the high idle situation? I have the same problem right now and the dealership cannot figure it out.

GMC to Ford

No. I cleaned the throttle body and reset the throttle position, but the issue still randomly occurs with 94000 miles on the truck.

Bluegrass

High Idle occurs at cold start up due to the Ambient outside Temperature detection from the outside Sensor and the Sensor part of the MAP-T inside the intake.
At this point, the fuel is Richened up to support cold starts.
As a result the Idle is raised as part of the process and comes down as the engine heats up as detected by the CHT Sensor.
Even in Hot starts, the Idle may go up but come down quickly for Emission reasons and Cat heating.
I would be looking at the CHT and engine Temps with a Scanner looking at live data to see if there is an abnormal reading present that could result in raised Idle speed...falsely, as a result.
Often a poor or intermittent ground involving the CHT sensor can have the effect and affect Trans shifting and Ox Sensor ground as these circuits are part of a Current flow for these functions.
May even be a sticking open thermostat.
The CHT Sensor is a dual element detector that is able to send info from cold to a fully over heating range because it is not in contact with the Coolant, only the metal of the head in a blind hole.
Good luck.