So, I have a 2003 Xtype 2.5L and on cold mornings it misfires on all 6 cylinders until the engine gets warm. It only happens intermittently when the temperature drops below 50F (10C). When I apply acceleration in neutral (or in drive) there is a 3-6 second delay in RPM increase, once above 2500 RPM the misfire stops, then when I let off the pedal and the RPM returns to idle it begins to misfire again.

I've replaced all six ignition coils, IMT seals, cleaned both the MAF sensor and throttle body, and I've smoked the system for a vacuum leak with no success.

The only codes my OBD2 throws is a misfire on all six cylinders and running lean on bank one and two. (Also bad catalytic converters, but that's a result of the misfire.)


I only know enough to be a little dangerous, which is why I've finally broken down and decided to come to the experts. Any and all help is appreciated.

Thanks,
-Zech

 

Hot engine, parked. Look at LTFTs at idle, then rev to about 2500 and look again. Were they quite big (say over 10) and drop nearer 0? If so you know you've an air leak not yet found.

Otherwise, tell us what LTFTs you see

 

Thanks, will do. I'll let you know how it goes.

-Zech

 

How many miles on this car, and when was fuel filter last changed? It's an inexpensive part and fairly simple DIY job. I'd estimate your local fast lube can put one in for about $50 if you didn't want to do it yourself. Here's a YouTube video on the job:

 

I apologize, I forgot to mention that I have replaced the fuel filter as well.
Also, the car has 163000 miles on it.

-Zech

 

Thanks for confirming, Zech. You mention having replaced the coils; what brand of spark plugs are you running, and how old are they? I'm only six months into owning my '04 3.0L (now at 109k miles), but I put in Denso Iridiums (sourced from Rock Auto) and they're working fine for me.