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Replaced IAC, now throttle is 'sticking'.

fetishfrog

NAXJA Forum User
Location
Denver, Co
Hey all

97 XJ, basically stock.

Threw engine code 25 and was not holding idle very well anyway. Replaced the IAC.

Now the idle hold fine but, when I am driving and let off the gas, often the engine will maintain whatever RPM it is at for a moment (a few seconds) before the torque converter disengages and the engine drops to idle.

The only reason I don't think it's a torque converter issue is 1. this was not an issue prior to replacing the switch, and 2. when I tap the brake/come to a stop, there's no issue. Torque converter disengages fine.

Although I suppose two unrelated things breaking at the same time is the most Jeep thing you can do, I am still chasing a stuck throttle hypothesis.

Any thoughts on where to start?
 
Genuine Jeep IAC or a cheap Chinese clone part ? As I recall what you describe is one of the symptoms of the last faulty IAC I replaced. Did you re-set the ECM after the part install ? Any binding in the throttle/kickdown/cruise control cables? Any binding of the throttle body butterfly valve, rust, weak springs, or other issues that inhibits the throttle return ?

This procedure will erase the 1996+ OBD-II “Adaptive Memory” stored inside the PCM and allow a new “Adaptive Memory” to be developed. After performing this procedure the PCM will re-learn and store into Adaptive Memory your engines performance characteristics. Perform these steps exactly as they are written, in the order they are written. This will cause the adaptive memory in the PCM to be erased and cause the PCM to go into Fast Learn adaptive mode.

Disconnect the POSITIVE battery Terminal clamp and touch it to ground ( not the battery negative terminal ) for 30 seconds. The engine block or the A/C compressor pump will work as a ground. (This is to discharge the PCM capacitors, which maintain the Adaptive Memory).

Reconnect the Battery Cable
Turn Ignition Switch to the “On” position but DO NOT start the engine
Turn Headlight “On”
Turn Headlights “Off”
Turn Ignition Key “Off”

The PCM Adaptive memory has now been flashed, or erased from the PCM. When you start the engine it will be running off a set of pre-programmed tables that come with the PCM from the factory. When you get the engine up to operating temperature the PCM will start to collect data for the “Adaptive Memory”. The PCM will collect data for Adaptive Memory for the first 50 Warm-up Cycles.
 
Check/replace the ASD relay.
It is cheap and quick
 
Hey all

97 XJ, basically stock.

Threw engine code 25 and was not holding idle very well anyway. Replaced the IAC.

Now the idle hold fine but, when I am driving and let off the gas, often the engine will maintain whatever RPM it is at for a moment (a few seconds) before the torque converter disengages and the engine drops to idle.

The only reason I don't think it's a torque converter issue is 1. this was not an issue prior to replacing the switch, and 2. when I tap the brake/come to a stop, there's no issue. Torque converter disengages fine.

Although I suppose two unrelated things breaking at the same time is the most Jeep thing you can do, I am still chasing a stuck throttle hypothesis.

Any thoughts on where to start?

Possibly a bad TPS, not signaling to the trans computer that you're off the gas?
 
Basic TPS testing should determine if TPS is faulty or not.
 
Just following up. The problem seemed to abate on its own. Not exactly reassuring but testing showed no problems. Perhaps something was sticking and now is not.

Anyhow, if it returns, I'll restart the thread.
 
As already suggested, the ECM was likely using stored data parameters from the old IAC to run new IAC. Once the ECM learned the parameters of the new IAC, it is running correctly.
 
Throttle return spring?
 
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