QuestionQUESTION: I have a 2000 Grand Cherokee with 77K miles and the 4.7 eng, auto trans. When you start the vehicle it revs up to around 1500 rpm and drops back down to 500 or so, sometimes lower. When you drive the vehicle it's fine until you come to a stop then the RPM drops way down under 500 and most of the time it stalls unless you pop it in nuetral and hit the gas. It will do the same thing if you are in park and rev the gas up to the 1500 range and let off the gas. Rpms will drop and car stalls. I plugged my scan tool in and no codes are present not even in history. I checked some of the data and the target IAC reading is 180 and so is the IAC steps. My short term fuel is between 0 & 10% while the long term is 1 to 6.4%. those readings seem off to me. My O2s are sweeping fine. The map reading is 1.1, vacuum is 18.5, inj pulse 3.5ms, tps is .59, IAT is 106 degrees and 3.01 volts, coolant temp 205. I also ckd fuel pressure at 52psi. It makes me think the IAC isn't doing it's job so I used my scanner to actuate it in both directions & it works fine. I also ckd for TSB's and one did show up for an idle issue back in 2001 but I did notice it had a reprogram sticker under the hood for #882. Not sure if this is related to my problem or not. I also ckd around for any vacuum lks and none found. I'm not sure if you ran into this or not. Any other questions let me know. Any help would be great. Thanks
ANSWER: how do u have all of the sensor reading? do u work for a shop?
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QUESTION: I used to have a shop, now I just work on my own cars & relatives vehicles. Still have my scanner. I live in Idaho.
Answerthere is a TSB for PCM update for this sorta issue
THIS BULLETIN SUPERCEDES TECHNICAL SERVICE BULLETIN 18-023-00 REV. A,
DATED DEC. 21, 2000, WHICH SHOULD BE REMOVED FROM YOUR FILES. ALL
REVISIONS ARE HIGHLIGHTED WITH **ASTERISKS**. THIS LATEST REVISION
NOW INCLUDES THE WJ - CALIF. EMISSION PACKAGE.
SUBJECT:
4.7lL Engine Performance Enhancements
OVERVIEW:
This bulletin involves selectively erasing and reprogramming the Powertrain Control
Module (PCM) with new software (calibration level 99Cal20 and 00Cal17)
MODELS:
2000 (AN) Dakota
2000 (DN) Durango
1999 - 2000 (WJ) Grand Cherokee
NOTE: **THIS BULLETIN APPLIES TO VEHICLES EQUIPPED WITH A 4.7L ENGINE.**
SYMPTOM/CONDITION:
Some vehicle engines may exhibit several of the following engine performance conditions:
1. Part throttle or wide open throttle spark knock.
2. **Sag or hesitation following a cold engine start (except WJ with Calif. emissions).**
3. Rough idle.
4. Idle sag when decelerating to a stop.
