2002 Intrepid 2.7L 123K mi. - Engine misfires at idle only. Hesitates some coming off idle but smooth through the rest of the R.P.M. range. It doesn't happen ALL the time, but increasingly more often than not. Sets the P0300 code. Installed new O.E. plugs and inspected coil packs for corrosion on conducters. No change. It is my wife's car, but when I drive it, it seems like it doesn't happen until the engine is warmed up. Any thoughts?

 

May be fuel related (low pressure...clogged up filter, when was the last one changed?).

 

That was kind of what I was leaning towards....a fuel delivery issue...but I hesitate to go that route because it is SO intermittent. Really it is a car that gets driven 7 days a week and it happens maybe once or twice a week. Seems to me a clogged fuel filter or a weak (or bad) fuel pump would cause the symptom all the time. Idle air control valve? egr valve? Catalytic converter? Maybe something is getting sticky with gunk and not operating like it should? I don't know. In answer to your question i haven't changed anything fuel delivery related on the car since I've owned it. I regularly run BG Products fuels system cleaner through it, does have a new PCV valve and fuel tank cap. I inspected vacuum lines and replaced a few questionable ones. I also get the "EGR System Malfunction" code set on a regular basis. Gotta love those intermittent problems!

 

What EGR code? There may be an indirect link... EGR system d/n come on line until engine temp is up. You said intermittent but "but when I drive it, it seems like it doesn't happen until the engine is warmed up.” Do you notice or feel the misfire or just get a code? The misfire detection is via the PCM monitoring the crankshaft speed variation but can be induced by fuel system (or other "false misfire") because the PCM can not determine if there is a clog in the fuel system (or other causes...a lean or rich condition, exhaust leak, poor compression etc).

Now assume the EGR is malfunctioning intermittently...if too much recirculated emissions were to dump into the engine because the response time was lagging behind RPMs. That may cause a false misfire code (I think). What do you think?

 

For the EGR it is the P0440 code. Sometimes sets the P0441 code as well. Yes, I definetly notice the misfire. It's not a false code for sure. When it does it, say at a stoplight, if you put it in park or neutral it quits misfiring. I have no idea whether it is related or not-can't see how it could be- but here goes-Now the wife tells me that every once in a while (maybe twice a week) when taking off from a stop it doesn't shift from 1st to 2nd...goes half a block at 10mph until it finally shifts. Obviously a transmission problem. She seems to think all of this started happening around the same time (misfiring and tranny shift problem). I cannot see how the two could be related. Anyway I'm going to drive it the rest of the week and weekend. I personally haven't experienced the tranny problem, but definetly the misfire at idle. Getting info out of the wife about what the car is doing is like pulling teeth.

 

By the way..never have received a transmission code. I have a scanner that I can read realtime data if that would help.

 

I had a transmission shift problem in the past. With my issue, I also had the speedometer go dead so it was easy to trace back to the speed output sensor on the trany (for the output shaft RPMs from the tranny to the PCM). Do you have any flux or odd speedometer issues?

There is also a speed input sensor from the transmission (for the RPMs of the input shaft of the transmission to the PCM). The PCM uses these for MANY systems to include: emission control and the idle air motor (to set air volume lean/rich) and engine timing (only used in timing computation when the engine is WARMED UP)!

If either one is bad, the PCM is supposed to be able to determine it and flag a code. I have however seen many faults go undetected in the past that were causing problems.

The sensors are not too expensive or hard to change. I’d say it’s worth a shot. If your speedo looks normal try the input sensor first. If it’s a fix, great. If not, keep the new sensor in and install a new output also.

For the location, to the top of the second gen forum and open the post “the holy grail” Go to pg 21-146.

Good luck,

Kurt

 

After reading your reply I think that is the best place to start. Those systems being tied together like that makes sense with the issues I am having. I really don't think the shift problem is mechanical or hydraulic because it is SO intermittent. I have done tranny flushes at 50k & 100K. The tranny shifts flawlessly (and firmly) 99% of the time. I'm driving it until it does it to me so I can experience it for myself - so far nothing. I will definetely check into replacing those sensors and let u know how it goes.

THANK YOU for your time and input!!

Jason

 

You're welcome. I hope it works out for you.

Kurt