Bad misfire at idle on cylinder 4, can't find problem

[FPGT24]

I posted here about three times before concerning the problem I have been having with my Mystique.

It misfires pretty bad at idle on cylinder #4. It will fire, misfire, fire, fire, misfire, misfire, fire, fire, a pattern like that. CEL will come on within ten seconds of it being started up and it flashes. When I drive the vehicle, the CEL will stop flashing and all cylinders are alive. However, when it goes into 4th gear (automatic), the engine shudders really bad. I thought it was the transmission going out, but i've held it around 1,500RPM-2,000RPM steadily when it was at a standstill in neutral, and the engine shudders then too. So its the misfire problem causing the shudder.

What could this be? Why would it only misfire bad at idle then run great till it shifts into 4th gear? When the engine shudders in 4th, the CEL is not flashing. The CEL stops flashing right after I take off and it starts flashing again when I slow to a stop.

I have been told its likely a bad injector on cyl 4. What else could this be? coil pack? I'm stumped. Plugs were replaced, and the wires look new.

Please help if you can. Thanks much.

 

[Lost Arrow]

I think if someone told me it was probably the injector, and I was stumped, I'd start there.

Then I would grab a service manual, and go down the symptoms list, and try everything, in the order listed, until it was fixed.

If none of that did it, I'd probably drive it with a miss, until I was done being pissed, and do it all again.

It's just a machine.

Cheers :blackeye:

 

[DuratecDave]

I am assuming since you know its a misfire on #4, you have a code reader & thats what it told you? Try swapping the plug wires at coil & at the plugs on cylinders 4 & 5. That, in my troubled reasoning, will prove or the coil pack/wires/plugs are good/bad. If the trouble follows to cylinder 5, put it back and replace the plug in #4, if trouble persists replace #4 new-looking plug wire, and if trouble persists replace coil pack. Used coil can be picked up at a salvage for the price of a pizza. If nothing else, you will have a new spare. (note: due to the length of the plug wires, you will likely have to remove them from their retaining clips at the motor mount & each head corner temporarily)

If cylinder #4 still misfires using #5's plug wire, you very well could have a bad or clogged injector. If clogged, the spray pattern will be affected at the different RPMs you describe. I'd get a bottle or two of the better injector cleaner. (Think $6, not .99) If still no joy, source a new/used injector. Added benefit to changing the injector is a healthy cleaning to the UIM, LIM, and TB.

You mention that the plug wires look new -- did you change them? If so, is this when the trouble began, or a result of the misfire? Same question with the plugs.

Hope this helps.

 

[FPGT24]

I am assuming since you know its a misfire on #4, you have a code reader & thats what it told you? Try swapping the plug wires at coil & at the plugs on cylinders 4 & 5. That, in my troubled reasoning, will prove or the coil pack/wires/plugs are good/bad. If the trouble follows to cylinder 5, put it back and replace the plug in #4, if trouble persists replace #4 new-looking plug wire, and if trouble persists replace coil pack. Used coil can be picked up at a salvage for the price of a pizza. If nothing else, you will have a new spare. (note: due to the length of the plug wires, you will likely have to remove them from their retaining clips at the motor mount & each head corner temporarily)

If cylinder #4 still misfires using #5's plug wire, you very well could have a bad or clogged injector. If clogged, the spray pattern will be affected at the different RPMs you describe. I'd get a bottle or two of the better injector cleaner. (Think $6, not .99) If still no joy, source a new/used injector. Added benefit to changing the injector is a healthy cleaning to the UIM, LIM, and TB.

You mention that the plug wires look new -- did you change them? If so, is this when the trouble began, or a result of the misfire? Same question with the plugs.

Hope this helps.

Strange thing happened today, I hooked my code scanner up and now it is also throwing a P0402 code along with the P0304 which it throws within 10 seconds of it starting up. P0402 is too much flow through the EGR system. I wonder if that could be the cause of the misfire? It misfires at idle and when i hold the throttle open steadily between 1,500-2,000 RPM, the engine sputters like its gonna stall and the RPMs go up and down but when i hold it steadily at that RPM, the check engine light stops flashing. Once the car gets up to speed the CEL will stop flashing and it will have full power till it shifts into 4th gear where the RPM band is around 1,500-2,000, then it will sputter again but the CEL doesnt flash. Very strange. Ive never seen anything like this and Im really stumped with it. Been trying to figure this out since February 1st with no luck.

 

[kcobra]

Check the egr solenoid. They can fail one of 2 ways
1. stays open never cutting flow of vacuum to egr valve, ie egr is getting vacuum and flowing all the time. This could be your problem. The part is only about 20 bucks so if it fails testing replace and clear codes.
2. never opens and the egr never seems vacuum.