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chris
chris, Auto Service Technician
Category: Car
Satisfied Customers: 59
Experience:  2 year tech degree and 13 years at chrysler,dodge and jeep dealership
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My car wont stay running unless my foot is on the gas.

Customer Question

I have a 97 Jeep Grand Cherokee. Randomlly when I first start it up it wont stay running unless I keep the gas applied. After running for awhile it works fine. Then happens acouple days later.
Submitted: 8 years ago.
Category: Car
Expert:  chris replied 8 years ago.
hows the battery on this veh? with out getting too detailed(unless you want the full version)if the battery is on the threshold of good/bad offten in the am after the car has sat for many hours when you start it the battery voltage drops below the recomended. and with electronics when the voltage drops too low things get weird. the IAC (idle air control motor) memory in the engine computer will get off and the veh will not idle for several minutes until the comp relerns the iac steps.There are MANY things that can cause this but thats the first thing that would come to mind if you brought this in to me at the dealership. I recomend you take it to a part store that does the free battery inspection and if it is on the low side of pass I would replace it. jumpping it wont help as once the voltage has spiked low and it stalls you have to drive it to get it to runn good again. hope this helps!
Customer: replied 8 years ago.
Reply to chris's Post: The battery was changed all ready. When the problem first accured I brought it into a shop and the insisted that the battery was the problem. I told them no I had the battery tested and it was fine. But continued to to assure me it would fix the problem. So I had them put a new battery in. Well it didnt happen again for a few weeks and so I though wow that was the problem. Then it started happening again. So I then tried some fuel injector cleaner a couple times and thought that helped a little. Then it did it again. So now what?
Expert:  chris replied 8 years ago.
hmmm. ok not to beat the horse here but do you have stuff like a cell phone charger,radar detector or any thing like that you keep pluged in all the time on a veh off live socket.there could be a draw on the battery and over time it will run a batt down.to check this you need an amp meeter that can mesure milli amps.since you said replacing the battery helped for a few weeks this would be my next test.there are lots of things that if not operating properly can draw the battery down.cell phone chargers were a big one that i have found.for the IOD (ignition off draw) test the milliamp spec is no more that 30 milli amps.Again there are many things that can cause this kind of problem(stall out)but based on the symptoms you are telling me I want to lean on the battery. if you are convinced this is not the problem then I have some other thoughts but are more technical. IOD test
1.     Verify that all electrical accessories are off. Turn off all lamps, remove the ignition key, and close all doors. If the vehicle is equipped with a illuminated entry system or electronically tuned radio, allow the electronic timer function of these systems to automatically shut off (time out) This may take up to three minutes.
2.     Determine that the under-hood lamp is operating properly, then unplug the lamp wire harness connector or remove the lamp bulb.
3.     Disconnect the battery negative cable.
4.     Connect a typical 12-volt test lamp (low-wattage bulb) between the disconnected battery negative cable clamp and the battery negative terminal post. Make sure that the doors remain closed so that the illuminated entry system is not activated. The test lamp may light brightly for up to three minutes, or may not light at all, depending upon the electrical equipment on the vehicle. The term "brightly," as used throughout the following tests, implies the brightness of the test lamp will be the same as if it were connected across the battery. The test lamp must be securely clamped to the battery negative cable clamp and the battery negative terminal post. If the continuity between the battery negative terminal post and cable clamp is lost during any part of the IOD test, the electronic timer function will be activated and all tests must be repeated.
5.     After three minutes, the test lamp should turn off or be dimly lit, depending upon the electrical equipment on the vehicle. If the test lamp remains brightly lit, do not disconnect it. Remove each fuse or circuit breaker (Refer to Wiring Diagrams for more information) until the test lamp is either off, or dimly lit. This will isolate each circuit and identify the source of the high-amperage IOD. If the test lamp is still brightly lit after disconnecting each fuse and circuit breaker, unplug the wire harness connector from the generator. If the test lamp now turns off or is dimly lit, Refer to Charging System to diagnose the faulty charging system. Do not disconnect the test lamp. After the high-amperage IOD has been corrected, the low-amperage IOD may be checked. It is now safe to install a milliampere meter to check the low-amperage IOD.
6.     With the test lamp still connected securely, clamp a milliampere meter between the battery negative terminal post and the negative cable clamp

CAUTION: Do not open any doors, or turn on any electrical accessories, with the test lamp disconnected or the milliampere meter may be damaged.
7.     Disconnect the test lamp. Observe the milliampere meter. The current draw should not exceed thirty milliamperes (0.030 ampere) If the draw exceeds thirty milliamperes, isolate each circuit by removing the circuit breakers and fuses. The milliampere meter reading will drop when the source of the draw is disconnected. Repair this circuit as required; whether a wiring short, incorrect switch adjustment, or a component failure is at fault.
Customer: replied 8 years ago.
Relist: I still need help.
The battery was changed all ready. When the problem first accured I brought it into a shop and the insisted that the battery was the problem. I told them no I had the battery tested and it was fine. But continued to to assure me it would fix the problem. So I had them put a new battery in. Well it didnt happen again for a few weeks and so I though wow that was the problem. Then it started happening again. So I then tried some fuel injector cleaner a couple times and thought that helped a little. Then it did it again. So now what?
Expert:  chris replied 8 years ago.
what brand and octane of gas do you use? when you have to keep it running does it run ok as long as you have your foot on the gas or does it run rough like it is missing?does it do it only on a cold start after sitting for 6 or 8+ hours or will it do it after sitting for 10 minutes or so?
Customer: replied 8 years ago.
Reply to chris's Post: I use the cheap gas. Lowest octane. It seems to run ok as long as my foot is on the gas. It only does it after sitting for over night or the weekend. Then once I get it going it takes a good distance before it will stay running. If I were to only go a short distance before the car really kicks in and I turn the car off, it will do it again. Once the car has drivin a while it will be pretty ok.
Expert:  chris replied 8 years ago.
the low octane is good,you may try a brand name fuel like mobil or bp just to rule that out(gas isn't gas)there is a motor bolted to the back of the throttle body called an IAC motor (Idle air control)that may be causing this. tipicaly when they malfunction it will stall out when comming to a stop but I have seen them do this sort of thing too. Also i would want to look at the ECT (enginge coolant temp sensor)when the veh was coold and make sure it was acurate to the outside temp.I have seen them show say 80df when the temp was 30df which is way to lean(computer adjusts fuel based on many inputs one of them being eng temp)and after running for awhile they show normal readings and everything is ok. with out a scan tool to check these and other things it may be next to impossible to diag this problem like this.you could try to clean the t-body with some carb cleaner (gumout) spray a little down the t-body blades and the opening on the top back(where the IAC gets its air)brush it with an old tooth brush(why doesnt the gumout melt the brush? which makes me ask what the hell is in our mouths that the brush needs to be built like that? then start it and while raising the rpms (say 1800)spray some in the t-body for a finish clean.both the Iac and ect sensor are not that expensive 25 to say 50 bucks I think(at the dealer)if you want to try something but i cant say for sure that it will cure your problem.hope you can get to the bottom of this and I will help any way that i can, IF and when this is fixed I would love an update on what did it.here is some info on fuel.SYMPTOM/CONDITION:

Long cold start times, warm-up sags, hesitations, and driveway die outs. These symptoms are most noticeable and severe at moderate ambient temperatures between 4 - 27 degrees C (40 - 80 degrees F).

DISCUSSION:

Gasoline with a high Driveability Index (DI) can cause the above described symptoms. DI is a measure of the gasolines total volatility, or tendency to vaporize completely. A high DI number is XXXXX volatile than a low DI number. Most premium gasoline sold in the U.S. has a higher (worse) DI index than regular or mid-grade gasoline. Use of premium gasoline is NOT recommended for vehicles designed to run on 87 (R+M)/2 regular or 89 (R+M)/2 mid-grade gasoline. High DI gasolines also cause higher emissions for the same reasons they cause driveability problems.

For vehicles that require an octane rating of 91 (R+M)/2, premium is recommended, or possibly required. Using premium fuel with a higher than recommended octane rating is not recommended. Owners who experience fuel related cold start and warm up driveability problems should try a gasoline with the recommended octane rating or different brands of gasoline until they find one that provides good performance.

The octane quality of gasoline is only a measure of its resistance to spark knock. The use of higher than recommended octane gasoline under normal operating conditions does NOT improve startability, idle quality, fuel economy, driveability, acceleration, engine durability, or emissions. In fact, most higher octane gasolines available in the U.S. have higher DI values than regular gasoline. Customers are most likely to experience poor driveability with premium gasoline than with regular.

Some vehicles, such as Viper, Prowler, 5.9L Grand Cherokee, 2.0L Turbo Talon, and 2.0L DOHC Neon have been specifically designed to take advantage of higher octane. These vehicles may have higher compression ratios, and/or more aggressive spark calibrations which provide optimum performance with the specified higher octane. However, other vehicles which are not specifically designed and calibrated to take advantage of higher octane will not benefit from higher octane.

Some vehicles may experience light spark knock in situations such as trailer towing or climbing steep sustained grades. Light knock or "ping" under these conditions is not harmful. However, if the customer is concerned about light knock under these circumstances, the use of 89 (R+M)/2 or even 91 (R+M)/2 premium gasoline may be temporarily warranted. If a vehicle is experiencing heavy spark knock on gasoline with its designed octane rating, this may be an indication of excessive combustion chamber deposits, or some other problem. Combustion chamber deposits can be removed with Mopar Combustion Chamber Conditioner p/n 04318001. Standard diagnostic procedures may help in identifying other potential causes of excessive knock.

Some gasoline marketers may advertise that their premium gasoline contains extra detergent additives. Under provisions of the Clean Air Act, ALL gasoline sold in the U.S. must contain effective deposit control additives. Nevertheless, if fuel injector or intake valve deposits are suspected of contributing to poor performance, occasional use of Mopar Fuel Injector Clean Up p/n 04549613 is a much less expensive way to maintain engine cleanliness than regular use of premium gasoline.

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