2000 Jimmy 4.3 vortec Hesitation

Problem: Hesitation/Lack of Power/Slow (Stumbling) RPM Increase on Acceleration from Idle or Cruise at Moderate Speeds. Occurs 70 - 80% every time. Can be Duplicated in Neutral in Garage. Condition occurs with Hot or Cold Engine. Vehicle always starts and idles normally, as if no problem exists

Parts Repaced in last 2 months: Fuel Pump & Sock Fuel Filter A/C Spark Plugs Dist. Cap & Rotor Spark Plug Wires Ignition Module (Coil Driver) MAP Sensor TPS Sensor

Injectors Chemically Cleaned 3X Fuel Pressure: 61 PSI (Pump Running) 58 PSI (Pump Off) 52 PSI (Engine Running at Idle) 57 PSI (Engine under Acceleration) Cam Retard at -7 degrees, CRK Learn - Successful No DTC's Set - No SES Light On All Grounds Checked and Seem to be Intact.

Scanner will indicate an indiscriminate random misfire, at times, on various cylinders, when cracking open throttle while parked, in neutral, when hesitation problem occurs.

Scanner indicates all other sensor readings normal and functioning correctly.

I am running out of hair to pull out, (and ideas), hoping for comments or suggestions.

thanks

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troublecode
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my 97 suburban does the same thing but only when it is hot. i am starting to think of installing a cooler thermostat. let me know when you figure out what is wrong with your jimmy. The only thing I don't see on your list is replacing the exhaust system. I did that on mine and its no better. Maybe a muffler shop can test to see if the exhaust system is plugged. I should have had mine tested before spending all that money.

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boxing

i found this post on another board Then I moved on to the Mass Airflow Sensor. I removed the airfilter unit, disassembled the Mass Airflow Sensor unit that is right behind the airfilter. It's a square metal block shape sandwiched in the flexible rubber air ducting. It also has an electrical connection to it. Just disconnect the electrical connector, pull the 4 torx screws out, carefully pull off the metal cover and then the MAS will pull right off. Be really careful with the MAS, it's expensive and delicate. I sprayed the daylights out of small sensor wires using CRC MAS Cleaner ($8 at PepBoys) but still two of the three wires still looked black in the center, thicker area of the wire. Almost a charred look ... I thought I was off to the parts store again. But I went ahead and got a pencil eraser (I read this in another post ... I didn't just think this up on my own) and VERY, VERY carefully rubbed the wires to get the gunk off. Be very patient and gentle! It did clean them up to where they looked like silver wires again. Then sprayed them again with the rest of the can of cleaner. Let everything dry about 20 mins and reassembled. My van is now running like it did years ago ... more power, better sounding and the SES Light went off on it's own! I have to believe that cleaning the Mass Airflow Sensor did the trick. Very, very easy to do.

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boxing

do.http://www.chevroletforum.com/m_8072/tm.htm I do hate to admit this, but cleaning the MAF Sensor did solve my problem. My SES Light was not on and I had no DTC's, (for MAF or anything else), and my scanner displayed the MAF signal responding normally or as expected

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troublecode

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