Question about 2002 Jeep Grand Cherokee

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Erratic idle Hey guys. As a tech myself, I went over the basics. smoked the intake for vacuum leaks. monitored o2 sensors. all within fuel trimk specs. cleaned t/body and replaced idle air control valve. reset fuel adaption and min. idle with MODIS(snap-on scanner). still no luck. It revs to about 1800 and stays for 1/2 minute after start up. hot or cold. also causing erratic down shift on decel. Do you know of a computer flash update as I've spent too much time with no answer.

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  • mechstress Aug 15, 2008

    yeah bro I'm trying to find out where to go . without paying another 15 bucks

  • mechstress Aug 15, 2008

    I clicked on your history whilw waiting for your reply and I got a stack line "0" error

  • chuckcloutie Sep 30, 2008

    Revs up to 2000 rpm when starting doesn't always go back down right away



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Hi this is CMV9 as i brought our chat back up it stated that you had disconnected the chat. i am wondering if you are still in need of my assistance or not. please let me know.

Posted on Aug 15, 2008

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  • Cameron Viseth
    Cameron Viseth Aug 15, 2008

    if we chat through here you can just rate the chat instead of paying again.

  • Cameron Viseth
    Cameron Viseth Aug 15, 2008

    thats ok i can still assist you through e-mail.

  • Cameron Viseth
    Cameron Viseth Aug 15, 2008

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Engine not revving out at times

black smoke is excess fuel entering the cylinders. and does not burn completely. poor fuel milage is also a complaint of black smoke from tailpipe.check your O2 sensor, your MAF sensor and for vacuum leaks. Could be air intake check your air filter, but probably the O2 sensor.The O2 sensor. located on the exhaust pipe prior to the muffler, looks like a spark plug with a wire that comes off the tip and leads into the wire loom.But the 02 sensor will turn the check engine light on.other intake components like sensors, fuel injectors and the fuel-pressure regulator.should be checked. good-day!

Apr 06, 2014 | 2007 Toyota 4Runner

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I can smell that my jeep is not burning all the fuel it is consuming and my fuel milage is down. There are no engine codes and it seems to have a decent amount of power. I have been running some fuel...

First thing I'd do is to remove the spark plugs and see how they look. Black plugs will confirm that something is causing it to run rich. I'd also look at the exhaust and see if there is any black smoke.
also check the running temperature of the engine (should run at near 210 degrees (f))...too cold can cause the computer to richen up the fuel mixture. If you smell raw fuel, take a good look at the fuel lines etc to make sure you have no leaks. Your throttle position sensor and map sensor have a large influence on fuel consumption as do the O2 sensors. In fact, all the engine sensors work together as the computer takes in all that information in order to decide where to put engine timing and fuel pulse length and frequency. It is possible to have one or more sensors just out of range enough to alter the fuel mix without setting a code. To find a problem like that you'd need to do individual component tests as outlined in chilton or haynes manuals, writing down your test results and comparing those to expected values also listed in the same publications. I'd also check all vacuum lines and for leaks at the intake manifold a small leak can change what the sensors see.
Tests take time and patience. They are necessary though.

Dec 10, 2010 | 1998 Jeep Cherokee 4WD

1 Answer

I have a 2003 Mercury Sable with engine code 1031 what is the problem,I need to get this corrected to have the car inspected.Thank you.

DTC P1031 - HO2S Heater Current Monitor Control Circuit Sensors 1

Its refer to the Oxigen Sensor; the most common issues for lean codes are:
1. Vacuum leaks - check for failed or loose vacuum lines, leaking intake gaskets, intake air tubes loose or any other source of un-metered air leaks (leaks after the Mass Air Flow Sensor)
2. Restricted fuel filter or bent/pinched fuel system lines
3. Incorrect input from other sensors, such as the Mass Air Flow Sensor, which may not always drop a separate code
4. Engine misfire – Yes I know this one may seem weird. You might think that if there is a misfire then you will have all that unburned fuel and it should read rich; right? Well the O2 sensors read only oxygen content in the exhaust, so if you have all that unburned fuel from incomplete combustion then, you guessed it, you also have all that unburned oxygen. High O2 content in exhaust equals a lean reading! There are also some other possibilities such as an internally leaking EGR system, (but this will typically set a separate code). A leak in the exhaust system before the O2 sensor will also cause incorrect readings. And always check for after- market modifications. These can throw a wrench into the works! The only other possibilities (however unlikely), are wiring issues, computer concerns or a bad O2 sensor! There now that I’ve said it, on to rich codes.

The possible causes of rich codes are:
1. A leaking or faulty fuel injector
2. Fuel injector driver in computer shorted, or wiring short for injectors (likely a ground short)
3. Leaking or faulty fuel pressure regulator or restricted return line
4. Faulty evaporative emissions system - bleeding fuel vapors into engine (not commanded by computer)
5. On newer models a faulty fuel pump or fuel pump driver module
6. Faulty readings from other sensors such as a Mass Air Flow Sensor. You may actually be getting more air than the MAF tells the computer
7. Exhaust leaks before the sensor will cause erratic readings
8. After market components or performance chips
9. And yes, if I dare say it, possibly a computer, wiring issue or even a faulty O2 sensor!

The other codes we should address are those related to the sensors located after the catalytic converter. Though these may appear identical to the oxygen sensors pre-converter, they perform an entirely different task and are known as Monitors. The only job of these sensors is to “monitor” the efficiency of the catalytic converters. The readings from these sensors should be much more stable and not fluctuating like the front O2 sensors. The computer compares the readings from the oxygen sensors (pre cats) and the monitors (post cat) to determine if the catalytic converters are doing their job and “cleaning” the exhaust. You never want to replace a monitor for a rich/lean concern as they have no bearing on these codes. As the converters begin to fail, you will see the monitors voltage readings follow the oxygen sensor readings. Technically these are all “oxygen sensors” but it is important to distinguish the difference between pre-converter & post converter sensors, so I find it easiest to stick to calling the back ones monitors.

Hope helps (remember rated this).

Jul 14, 2010 | 2003 Mercury Sable

2 Answers

91 S10 rough idle, stalling ALDL problems

Make sure there is no vacuum leaks.

Vacuum leak at intake manifold and vacuum hose.

Bad Idle Air Control Motor (IAC)

Low compression (170 psi + is OK)

Start cleaning and repair these trouble spots and see is there any improvement.


For more advance DIY'er then you may try this.

Use a can of Berryman carburetor clean to locate the vacuum leak.


This is a 20-30 minutes job.

Vacuum leaks can occur in following locations.

Intake manifold AND/OR vacuum lines.

Intake manifold is not accessible unless the engine head if off.

You can still check the potential leak by spraying some Berryman near the intake manifold.

Listen for rpm increase after you introduce the Berryman (FUEL) at idle.

Do the same starting from the brake booster unit (the round unit) on the drive side fire all.

Carefully listen for increase of RPM right after to spray the Berryman to the potential vacuum spot.

Get a friend to HEAR the RPM increase or monitor for RPM on the tech.

DO NOT AIM the Berryman into any heat source.

PLEASE RATE my answer if it is useful to you.

Dec 17, 2009 | Chevrolet S 10 Cars & Trucks

2 Answers

1998 318ti erratic idle

you probly have a vaccum leak they are hard to find but make a very noticable difference when you find them. touch all small hoses untill you find something that changes

Oct 31, 2009 | 1999 BMW 318 ti

2 Answers

Rough idle

Scan the engine, look for codes, then look at fuel trim, O2, and MAS readings for a clue. If it's running lean, you may have an air leak on the intake side. If all checks out, then look at plugs, injectors, coil packs. Probably need to have scanned with equipment that can detect these failures.

Oct 20, 2009 | 2005 Cadillac Escalade

2 Answers

Erratic high idle

most of the time its the throttle pos sensor

Oct 13, 2009 | 1990 Nissan Sentra

2 Answers

Misfires at idle speed

CEL code or just hear the popping?

First check wires, plugs, coil pack, cam and crank sensors, basic timing, MAF, EGR system, fuel filter and fuel pump.....basically it is probably running lean

Jun 30, 2009 | 2000 Mazda MX-5 Miata

3 Answers

All 4 o2 sensors read bad

daves944 knows what he is talking about, u need to find the root cause of this problem, which is a problem any of th following can cause this, MAF, Intake leaks, engine conditions like low compression and many other things, the O2 codes are a Symptom not the problem, you may also have a wiring harness problem, check the harness connectors to the O2 sensors, look for exhaust heat related wiring damage, look for corrosion in connectors.

May 01, 2009 | Ford F-150 Cars & Trucks

1 Answer

2000 BMW 323i Check Engine Light Problem-10 codes!!! Help!

I would first check for a vacuum leak. Common areas of intake leaks are: 1. The crankcase vent valve located under the intake. 2.Check the intake boot at the throttle housing. You will find that there is an elbow where a small hose goes to your idle valve. Using your hand feel in the elbow area for a hole in the rubber. Your tech can use brake cleaner and spray the intake to check for leaks or use a smoke tester. 3.Possible failing Mass Air Meter.At idle, in park, and a/c not on the meter reading should be appr. 18-22 hz

Mar 06, 2009 | 1999 BMW 323 Series

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