2000 Jeep Grand Cherokee / 4.7 liter engine/ stalling near idle speeds

This car has 245K miles on it. At very low speeds of maybe 10-15 mph, or when stopped at a stop sign, the engine will stall. No problems on initial crank, and NO problems at any speed other than at or near low idle. Engine will always restart, but sometimes hard to get into gear again and get going, as it stalls again at such low speed. So, to get it going, I have to keep the idle up to about 1000 rpm and then shift it real quick to drive, and take off.

I have noticed however, that in order to get it cranked again, I have to hold my accelerator pedal down to the floor. This has **never** been needed before, either when the engine is cold is hot.

Put in new CPS about a year ago. I am NOT a mechanic, but this seems to me like a fuel related problem, such as a fuel filter or fuel pump. Is it hard to "test" a fuel pump ?

Please give me some tips on this so that I can better discuss it with my mechanic.

Remember, no problems EVER above 20 mph, and no problems ever on initial crank.

Thank you !!

James

Reply to
James
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Reply to
Scott in Baltimore

then shift it real quick to drive, and take off.

needed before, either when the engine is cold is hot.

First off you need to pull the engine codes.

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the way, that's also a good site for information.

WOT (Wide Open Throttle) signals the ECU to go into "bypass mode" meaning a sensor is failing. But not always.

How dirty is the throttle body and the idle-air-passage? From a 4.0.

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that gets crudded up it can cause stalls. Will the Jeep start with just a light amount of depression on the gas pedal? If so then I'd suspect the IAP. This also makes the engine run rough.

It could still be the CPS. :(

Fuel filter and pump commonly cause pinging at high RPM and power sag on the highway.

Another possibility is a failing or weak coil or in the older system, bad spark plug cables. Even a bad plug. But that usually causes a stammer/shake and a WOT start won't help.

Could be the CPS plug is dirty. Follow the CPS lead up to the connector and disconnect/clean/reconnect.

Reply to
DougW

Thanks Doug and Scott, good ideas !!

Any other comments/ advice from the group ?

James

Reply to
James

My 4.0 (and several GM products) had more trouble with the TPS (sensor or connector) than anything else at idle but I know several mechanics who make a practice of cleaning the IAC port and pintle as the very first step.

Reply to
Will Honea

Update:

Auto shop did a scan with OBD tool, but it pulled no codes. Here is a summary of all the possibilities that have been mentioned here, as to why my car doesn't like to run at idle. Oh, btw, I have noticed that this problem is much worse when the car is cold. It will still cut off at idle at other times, but the problem is quite severe when the car is first cranked up in the morning.

On the following list, I have had the items repaired, cleaned, or replaced in the last year or so:

-----------------------------------

cps / done recently

cps plug/ maybe needs cleaning ?

tps /

gummy throttle body/ cleaned about a year ago

fuel pump / never been replaced

fuel filter / never replaced

idle air control/

manifold air sensor/ never replaced

vacumm leak ? // could be, but mechanic said would usually make it run lean, and pull a code

idle air passage / cleaned when throttle body cleaned about a year ago

weak coil/ and/or bad spark plug or cables/ ?? has original coil

---------------------------

On a cold morning, the car will start right off, run a second or two, then shut off. I may have to crank it 4 or 5 times to get the rpm up enough that I can throw it in gear and take off. At very low speeds of maybe 10-15 mph, or when stopped at a stop sign, the engine will stall. NO problems at any speed other than at or near low idle. Engine will always restart, but sometimes hard to get into gear again and get going, as it stalls again at such low speed. So, to get it going, I have to keep the idle up to about 1000 rpm and then shift it real quick to drive, and take off.

Any more ideas here ? Why is it more severe when engine is cold, first thing in the morning. I am not a mechanic, but it seems that should be a big hint....

Thank you !!

James

----------------------------

This car has 245K miles on it. At very low speeds of maybe 10-15 mph, or when stopped at a stop sign, the engine will stall. No problems on initial crank, and NO problems at any speed other than at or near low idle. Engine will always restart, but sometimes hard to get into gear again and get going, as it stalls again at such low speed. So, to get it going, I have to keep the idle up to about 1000 rpm and then shift it real quick to drive, and take off.

I have noticed however, that in order to get it cranked again, I have to hold my accelerator pedal down to the floor. This has **never** been needed before, either when the engine is cold is hot.

Put in new CPS about a year ago. I am NOT a mechanic, but this seems to me like a fuel related problem, such as a fuel filter or fuel pump. Is it hard to "test" a fuel pump ?

Please give me some tips on this so that I can better discuss it with my mechanic.

Remember, no problems EVER above 20 mph.

Thank you !!

James

Reply to
James

Maybe a clue here - it took me months to get an 88 MJ to idle right with similar cold clues. When I had tried everything else, I changed out the O2 sensor. I didn't think about it causing the idle issue but the tailpipe told me that it was running rich at idle and changing the sensor did the trick. I've since learned a bit more about the O2 sensor and the one I have has a heater in it that can fail. The sensor will work fine once it heats up but without the heater element working it takes a while for the exhaust heat to do the trick.

I still have a nuisance with cool (not cold) days. Seems like as the weather warms in the Spring and cools in the Fall there is a range where the !@#$% thing dies at the first stop sign. Starts fine, idles fine but that first stop kills it. All is well if it's warm or cold but that in-between temp is a PITA. I still can't figure that one out but after 10 years I guess I can live with it.

This is an outside WAG but you've tried everything else so look for smoke/soot on that cold start that would indicate a rich mixture and a lazy O2 sensor. Easiest way to see it is to start it when it's still dark out. Put a strong flashlight or spot light shining through the exhaust stream and it will make it easy to see the fine emissions.

Reply to
Will Honea

Not everything will store a code. So when you have problems and no apparent code it's time to check them.

- weak O2 sensor (usually also gives you crappy gas mileage)

- spark/coil/plugs (no sensors on them)

I'd zero in on this next.

There is a test device for coil strength.

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variants on that. The problem is you have COP (Coil On Plug) so the ol standby won't help. :( You can install one of these between the COP and the spark plug but there is an easier way.

So let's get low tech on it's ass.

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The high tech method. Most folks don't have this at home. :)
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Reply to
DougW

Thanks, Will and Doug !!

James

Reply to
James

I haven't seen it mentioned but by 245k ... you might not have functioning O2 sensors in the exhaust.

There are 3 or them on the 4.7 - one each side ahead of the quick CATs and one after the main CAT.

On my '99 YJ (4.0 so there was only one) the front 02 sensor went bad and it would stall during warm-up unless near WOT. It didn't throw a code and a nearby independent mechanic mis-diagnosed it as a MAP sensor (some of you will remember my rant).

SFAIK there isn't an easy way of diagnosing the problem except through symptoms.

Cold start OK During warm-up prone to stalling except when feeding throttle When warm can be OK or rough at idle Poor fuel consumption

reboot (yes, I still lurk)

Reply to
reboot

I am glad to report that this problem has now been fixed. My mechanic had to replaced the idle air control motor. It is running good now, no stalls at idle speed.

Thanks for all the helpful advice given here.

James

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Reply to
James

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