Bought Grand Cherokee. Have a few problems. - Page 2 -
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post #16 of 16 Old 12-31-2003, 06:26 AM Thread Starter
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Join Date: Dec 2003
Posts: 94
Originally Posted by RockPaws
If its neither the IAC or TPS, I would take it some where and have the computer checked. I do not like throwing parts at a problem to see what fixes it. (we call it "Shotgun Maintenance").

Here is what the PCM looks at idle mode, at operating temp (closed loop). Inputs to the PCM:
1) A/C select signal
2) A/C request signal
3) Battery voltage
4) Crankshaft position sensor
5) Eng coolant temp sensor
6) Intake manifold air temp sensor
7) Manifold absolute pressure (MAP) sensor
8) TPS - throttle pos sensor
9) Camshaft position sensor (is distributor)
10) Park/neutral switch
11) O2 sensors
Based on these inputs - voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM wil them control injection sequence and injector pulse width by turning on and off voltage to each injector, thru its ground circuit.

The PCM monitors the O2 sensorsinput and adjusts air fuel ratio by injector pulse width. It also adjs eng idle speed thru the idle air control (IAC motor).
The PCM also adjs ignition timing by inc or dec spark advance.
Well I would rater place a couple sensors that are at 118,000 miles then adjust the idle least yet. I do know that should all be controlled with the computer that rec. the data from the if there is a bad sensor it is sending faulty data to the computer which in turn is not letting it adle correctly. I already bought the TPS sensor so I will replace it then I will take it to a stealership so they can charge me $50 to put there comptuer on it.


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