I recently picked up a 99 Max. Auto. Nice car and all and so far has been great. Since I picked it up I have noticed a weird issue. As the car is at idle or coming down to idle when stopping. The car will kind of thump, as well as lose a little bit of RPM. It usually does it about every 20-30 sec. Tonight it was doing it about every 5 sec., so it is getting worse. It happens randomly when I drive it, meaning some days it does it some days it won't. Otherwise the car drives great and as far as I can tell it hasn't effected it's performance. Oh and I also just recently replaced the rear o2 sensor/reset the ECU.

Any help with this issue would be great.

Thanks in advance.

 

A 99 that has a bump in the idle generally has bad coil packs.

 

coil packs! had exact same problem with my 99....got new coils from autozone and installed in about 45mins...f the dealer..they wanted $800...i did it myself for $410. oh and my autozone coils are still working perfect and ive had them for about 4-5 months (some people tell you that autozone coils wont work very well, i dont believe them from experience.)

 

Autozone sells our ignition coils now?
very interesting...

 

yea, they only carry 1 front bank and 1 rear bank though, so i had to go to 3 different stores unless i wanted to wait like a week

 

Isn't there a clutch on one of the accessories (is it AC compressor?) that kicks in every now and then. Mines always had that kinda click/bump then a slight increase in revs.

Doesn't sound like trouble to me?!?!?

 

These guys are correct. I had the same symptom for months and it was a dying coil pack. 6 new coils and a set of spark plugs later, no more bump!

When it's a coil, the RPMs 'bump' down (not up) maybe 150-200 from regular idle and then back to normal repeatedly. At least that's what my dying one was doing.

 

a bump and then an increase in revs may just be a downshift coming from the auto

 

Please tell me how is a bad coil pack cause a car to have a bad idle?

Please take a look at this and tell me if it make sense.....


The Engine idle is un-balanced and is hunting.
Follow this link for, CASE HISTORIES
THE SLOW RETURN TO IDLE PROBLEM MAY OCCUR IF BATTERY POWER IS DISCONNECTED FROM THE ECU, OR IF THE BATTERY HAS BEEN RECENTLY FLAT.
THE CAUSE OF THE SLOW TO RETURN TO IDLE IS THE EEC IV COMPUTER NOT KNOWING WHERE THE T.P.S. IS POSITIONED.
REMEDY - TO RE-ESTABLISH THE IDLE MEMORY INTO THE EEC IV COMPUTER DO THE FOLLOWING :
* START THE ENGINE AND ALLOW IT TO REACH NORMAL OPERATING TEMPERATURE.

* ALLOW THE ENGINE TO IDLE FOR AT LEAST 30 SECONDS AT OPERATING TEMPERATURE IN NEUTRAL POSITION, IF A MANUAL OR IN DRIVE IN AN AUTOMATIC.

*NOTE ALL ACCESSORIES MUST BE TURNED OFF WHILE IDLING.

Follow this link for, " KNOW HOW"
CAUSE: - A FAULTY CONNECTION AT THE IDLE SPEED CONTROL MOTOR D.C. IS RESPONSIBLE FOR THIS.
REMEDY - REPAIR THIS CONNECTION AND RETRY.

CAUSE: - THE IDLE SPEED CONTROL MOTOR slide IS RESPONSIBLE FOR THIS. (jammed, lifted by carbon build up etc.)
REMEDY - REPAIR THIS FAULT WITH THE INTER-JECT SERVICE ONLY!

CAUSE: - THE OPTICS MODULE AND PLATE IN THE DISTRIBUTOR IS DIRTY CAUSED BY A FAULTY SHAFT SEAL AND ENGINE BACK PRESSURE OILS ALL COMPONENTS INSIDE THE DISTRIBUTOR (NISSAN, VL, RODEO. ETC.)

CAUSE: - SOME ONE ALTERED THE THROTTLE BLADE STOP.
EA, EB, GAS CONVERSION FITTERS DO THIS, AND ALSO CAR OWNERS THEM SELF'S TO IMPROVE IDLING CHARACTERISTICS.
THIS CAUSES A CONFLICT BETWEEN OXYGEN SENSOR, ECU, AND THE IDLE STABILISER VALVE.
REMEDY - SET THE BUTTERFLY STOP TO CLOSED, DO A FULL INTERJECT SERVICE.

PROBLEM - ENGINE MISFIRING, ENGINE HUNTING AND INTERMITTENT FLAT SPOTS.
CAUSE: - FUEL PUMP.
REMEDY - REPLACE THE FUEL PUMP.

PROBLEM - FUEL STARVATION. CAUSE: - PLASTIC STRAINER AT THE FUEL PUMP INLET BLOCKED. REMEDY - BACK FLUSH AND CLEAN THE STRAINER WITH INTER-JECTRON.
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The Engine has a very bad hesitation on acceleration.(flat spot)
Follow this link for, CASE HISTORIES
Most common faults as follow:
1. T.P.S SWITCH, TEMP SENSOR, DIRTY INJECTORS, FUEL PRESSURE REGULATOR BELOW REQUIRED SETTING, AIR FLOW METER FAULTY, CARBON ON THE BACK OF THE VALVES IS THE MOST COMMON FAULT
REMEDY:- A FULL INTER-JECT SERVICE WITH THE LB-291/2F IS REQUIRED!
2. WATER IN FUEL, (it's very common), FUEL FILTER, FUEL PUMP, LEAKY FUEL PRESSURE REGULATOR.
3. SPARK PLUG, LEADS, CONNECTORS, DISTRIBUTOR CAP, COIL PACK, IGNITION MODULE, IGNITION TIMING, WRONG FUEL WITH LOWER FLASH POINT AND OCTANE RATING.
4. VACUUM LEAKS ABOUT THE MANIFOLD AREA AND AIRFLOW METER, MAP SENSOR AREA,
5. SYSTEM IS NOT MATCHED PROPERLY TO A NEW OR SECOND HAND ENGINE, WRONG INJECTORS FITTED TO A LARGER ENGINE, STANDARD INJECTORS FITTED TO A TURBO ENGINE.
5. CAM BELT, VALVE TIMING, BENT OR SLIGHTLY BURNED VALVE, VALVE TO TIGHT, DISTRIBUTOR GEAR WORN, DISTRIBUTOR NEEDS REGRAPHING,
6. HIDDEN RESISTOR FITTED BY SOME ONE INTO THE TEMP CIRCUIT TO FOOL THE COMPUTER, SHORT OR DISCONNECTED AIR TEMP WIRING
7. THROTTLE BODY VERY DIRTY AND NOT CLOSING PROPERLY, ACCELERATOR CABLE FAULTY OR WRONG ADJUSTED, CRUSE CONTROL FAULTY.
8. WATER IN THE COMPUTER OR CORROSION ON THE CONNECTORS, VOLTAGE DROP FROM THE BATTERY, BAD EARTH.
9. ALTERNATOR DIODES FAULTY, TO MUCH AC CURRANT INTERFERING INTO THE DUTY CYCLE CURRENT OF THE IDLE STABILISER VALVE.
10. ECU RANDOM ACCESS MEMORY FAULTY, ECU NOT SET TO TPS LOCATION.


PROBLEM - INTERMITTENT NO SPARK. FUEL PUMP WORKING O.K.
CAUSE: - LOOSE EARTH CONNECTION ON THE RIGHT HAND STRUT TOWER.
REMEDY - REPAIR THE EARTH AND TIGHTEN.

CAUSE: - FAULTY HALL SENSOR IN DISTRIBUTOR.
REMEDY - REPLACE HALL DEVICE.

CAUSE: - INCORRECT ROUTING OF THE AIR CONDITIONING COMPRESSOR WIRING CAN INTERFERE WITH THE CRUISE CONTROL THROTTLE LINKAGE.
REMEDY - RELOCATE THE WIRING AWAY FROM THE THROTTLE LINKAGE AND SECURE IT WELL AS SO IT WILL NOT AFFECT ANY OTHER MOVING PARTS OF THE ENGINE.

PROBLEM - STALLS WHEN ACCELERATOR IS USED. IDLES GOOD THOUGH.
CAUSE: - FAULTY THROTTLE VALVE SWITCH.
REMEDY - REPLACE THE THROTTLE VALVE SWITCH.

PROBLEM: - THE ENGINE WOULD START O.K. AND RUN AT IDLE O.K., BUT WHEN THE CARS ACCELERATOR WAS USED, IT WOULD NOT ACCELERATE.
CAUSE: - THE FUEL PUMP WAS FOUND TO BE FAULTY.
REMEDY - REPLACE THE FUEL PUMP.

PROBLEM - THE ENGINE WOULD START BAD. RUN AT IDLE O.K., BUT WHEN THE CARS ACCELERATOR WAS USED, IT WOULD NOT ACCELERATE.
CAUSE:- THE FUEL PRESSURE REGULATOR WAS FOUND TO BE FAULTY. (LEAKING BADLY)
REMEDY - REPLACE THE FUEL PRESSURE REGULATOR ONLY AFTER AN ATTEMPTED CLEANING PROCESS WITH INTER-JECTRON. IF NO GO REPLACE THE REGULATOR.
The Engine has a hesitation only just above idle by moving the accelerator slightly. (noticeable flat spot)
Follow this link for, CASE HISTORIES
Most common faults:-
1. FAULTY SPARK PLUG LEADS, LEADS ARCING ACROSS, IMPEDANCE TO HIGH, WRONG TYPE OF SPARK PLUG, GAP TOO FAR APART, COIL, COIL PACK FAULTY.
2. T.P.S. CONTACTS DIRTY, WRONG ADJUSTED OR FAULTY.
3. THROTTLE SHAFT WORN, BUTTERFLY WORN ON THE EDGES, DIRTY THROTTLE BODY, AIR LEAK IN GENERAL.
4. AIR FLOW METER OUT OF CALIBRATION. (SEE CALIBRATION IN THE DATA POOL) |Trade-Secrets|
5. BRAKE POWER BOOSTER AIR LEAK, BOLT OR NUT LOOSE NEAR THE POWER BOOSTER HOSE CONNECTION ON THE INTAKE MANIFOLD OR GASKET LEAK.
6. OXYGEN SENSOR FAULTY, NO GOOD EARTH, EXHAUST HAS NO GOOD EARTH.
7. WORN DISTRIBUTOR, OR WORN DISTRIBUTOR GEAR.
8. VACUUM ADVANCE NOT WORKING, SPOUT WIRE NOT CONNECTED, ALTERNATOR EARTH POOR, POWER TRANSISTOR FAULTY.


CAUSE: - CHECK ALL EARTHING POINTS ARE UNDER 0.03V.
IF ANY ARE OVER THIS, THERE MAY BE PROBLEMS WITH THE CARS FLAT SPOT ABOVE IDLE.
REMEDY - REPAIR / REPLACE EARTHS.

SYMPTOM - SPARK PLUGS FOULED, DUE TO OVERFUELING.
CAUSE: - FAULTY ECU.
REMEDY - REPAIR / REPLACE ECU.

PROBLEM - MISFIRING AND STALLING WHEN UNDER LOAD CONDITIONS. CAUSE: - ROTOR BUTTON HAS BURNT OUT.
REMEDY - REPLACE THE ROTOR BUTTON WITH THE GENUINE PART ONLY.

CAUSE:- INTEGRATION IGNITION ASSEMBLY (I.I.A.)
PICK-UP COIL WIRES INSULATION RUBBED THROUGH AND WERE INTERMITTENTLY SHORTING.
REMEDY - RE-INSULATE THE WIRES AND RE-ROUTE THEM.
| Shortcut back to Menu for more faults |
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The Engine has a hesitation only just above idle by moving the accelerator slightly. (noticeable flat spot)
Follow this link for, CASE HISTORIES
Most common faults:-
1. FAULTY SPARK PLUG LEADS, LEADS ARCING ACROSS, IMPEDANCE TO HIGH, WRONG TYPE OF SPARK PLUG, GAP TOO FAR APART, COIL, COIL PACK FAULTY.
2. T.P.S. CONTACTS DIRTY, WRONG ADJUSTED OR FAULTY.
3. THROTTLE SHAFT WORN, BUTTERFLY WORN ON THE EDGES, DIRTY THROTTLE BODY, AIR LEAK IN GENERAL.
4. AIR FLOW METER OUT OF CALIBRATION. (SEE CALIBRATION IN THE DATA POOL) |Trade-Secrets|
5. BRAKE POWER BOOSTER AIR LEAK, BOLT OR NUT LOOSE NEAR THE POWER BOOSTER HOSE CONNECTION ON THE INTAKE MANIFOLD OR GASKET LEAK.
6. OXYGEN SENSOR FAULTY, NO GOOD EARTH, EXHAUST HAS NO GOOD EARTH.
7. WORN DISTRIBUTOR, OR WORN DISTRIBUTOR GEAR.
8. VACUUM ADVANCE NOT WORKING, SPOUT WIRE NOT CONNECTED, ALTERNATOR EARTH POOR, POWER TRANSISTOR FAULTY.


CAUSE: - CHECK ALL EARTHING POINTS ARE UNDER 0.03V.
IF ANY ARE OVER THIS, THERE MAY BE PROBLEMS WITH THE CARS FLAT SPOT ABOVE IDLE.
REMEDY - REPAIR / REPLACE EARTHS.

SYMPTOM - SPARK PLUGS FOULED, DUE TO OVERFUELING.
CAUSE: - FAULTY ECU.
REMEDY - REPAIR / REPLACE ECU.

PROBLEM - MISFIRING AND STALLING WHEN UNDER LOAD CONDITIONS. CAUSE: - ROTOR BUTTON HAS BURNT OUT.
REMEDY - REPLACE THE ROTOR BUTTON WITH THE GENUINE PART ONLY.

CAUSE:- INTEGRATION IGNITION ASSEMBLY (I.I.A.)
PICK-UP COIL WIRES INSULATION RUBBED THROUGH AND WERE INTERMITTENTLY SHORTING.
REMEDY - RE-INSULATE THE WIRES AND RE-ROUTE THEM.
| Shortcut back to Menu for more faults |



http://www.users.bigpond.com/INTERJE...20is%20hunting.

 

if the coil pack has a different resistance then it was originally, it wont fire the cylinder fullyor at all, which in turn wont burn all the fuel or give a spark, which could cause an erratic idle or misfire

 

Misfire it is different then idle problem. Don't get that confused. Read the above statement, try to use your common sense. Usually a bad coil pack could cause major peformanace issue not idle problems like that. Misfire it is not consider idle problem, misfire is misfire. you can't miss a misfire, you will def feel it.

 

if the car is misfiring, he may not know its misfiring and to him it is idleing different than it used to. some people may be able to tell the diffrerence between a regular bad idle and misfire but someone that doesnt know much about their car or just got it may not know. a misfire would for sure throw a code

 

How could you not know your car is misfiring? Your car will run like crap. There will be a lot of hesitation When you step on the gas. Misfire = Performance issue...

I am sure most people would know about that.