2.5 slow to return to idle

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Wingnut537

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Jun 9, 2021
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Arizona, Louisiana, Florida
Ok so last week I cleaned the throttle body with some crc throttle body cleaner, I let it take some in through the IAC several times. I did this to resolve a bit of a rough idle and it did the trick. Now after a few days of driving it has a new issue.
When coming to a stop the rpm hangs at about 1500 and will slowly come down to idle (10-15 seconds). If I wait until the revs are down below 1000 before depressing the clutch then all is as it should be.
Today I took off the IAC and cleaned it, it was dirty but you could tell that last weeks cleaning while running did do some cleaning. I have searched for a vacuum leak to no avail. And there are no codes or check engine light.
Ideas?
 
When cleaning the throttlebody you should really remove the IAC, clean both the disc and seat along with the port that goes thru to the inside of the throttlebody throat. Not cleaning the disc and seat can cause sluggish response or debris to remain which will cause an idle high issue.
 
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CharlesHS said:
When cleaning the throttlebody you should really remove the IAC, clean both the disc and seat along with the port that goes thru to the inside of the throttlebody throat. Not cleaning the disc and seat can cause sluggish response or debris to remain which will cause an idle high issue.
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I did that today thinking this was the issue from last weeks cleaning, no change.
 
Wingnut537 said:
I did that today thinking this was the issue from last weeks cleaning, no change.
Click to expand...
I also clean the shaft of the solenoid where the disc is attached. There are times when the IAC solenoid is sluggish to respond due to resistance buildup in the coils windings. Check the connector terminals for greyish residue and clean as needed.
 
Disconnect your linkages see if the throttle plate snaps back closed. Remove TPS and do the same. See if there is a difference. I have seen videos where the bushings in the trottle body and the shaft for the trottle plate get worn maybe causing your issue.

I have an extra return spring on the linkage. I was having idle issues with my 2.5. It would stay high. I would quickly tap the gas peddle to get it to come down. Similar to a sticking choke on a carb. After a few days of that the TPS finally threw a code and I replaced it with a Mopar TPS
 
Ok, this morning I removed the TB, disassembled, cleaned, reassembled, and reinstalled. No change. Throttle snaps back as it should.
I can hear air rushing through the IAC port till the revs come down so I do believe it is a bad IAC. Is there a test I can do on it rather than just throwing parts at it?
 
Wingnut537 said:
Ok, this morning I removed the TB, disassembled, cleaned, reassembled, and reinstalled. No change. Throttle snaps back as it should.
I can hear air rushing through the IAC port till the revs come down so I do believe it is a bad IAC. Is there a test I can do on it rather than just throwing parts at it?
Click to expand...

In the FSM (which you can download here for free) there should be a procedure outlined for testing the IAC.
 
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Chris said:
In the FSM (which you can download here for free) there should be a procedure outlined for testing the IAC.
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Thanks Chris,
Unfortunately the test is going to require equipment that cost more than the part it seems.

"IDLE AIR CONTROL (IAC) MOTOR
To perform a complete test of the IAC motor and
its circuitry, refer to DRB scan tool and appropriate
Powertrain Diagnostics Procedures manual."
 
Wingnut537 said:
Thanks Chris,
Unfortunately the test is going to require equipment that cost more than the part it seems.

"IDLE AIR CONTROL (IAC) MOTOR
To perform a complete test of the IAC motor and
its circuitry, refer to DRB scan tool and appropriate
Powertrain Diagnostics Procedures manual."
Click to expand...
Oh yeah, the DRB tool. Any reputable Jeep mechanic will have one, but they aren’t cheap on the secondhand market for sure.
 
May want to look at the condition of the throttle plate shaft to see if there is excessive play. The newest 2.5 throttle bodies are now 20 plus years old and a worn shaft can cause weird idle conditions and cleaning it may have removed crap providing a seal.
 
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TJ4Jim said:
May want to look at the condition of the throttle plate shaft to see if there is excessive play. The newest 2.5 throttle bodies are now 20 plus years old and a worn shaft can cause weird idle conditions and cleaning it may have removed crap providing a seal.
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I did this morning. Minimal play and smooth. It is 24 years old but it's only got 119k miles.
 
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