Misfiring, was intermittent, now less so...

[GPX]

My car started misfiring at the end of my 35 minute commute a few weeks ago. My mechanic found a cracked plug. The car seemed great the little it got driven that night, but the next day, started missing at the end of my trip.

 

Fast forward to today: fuel injectors have been tested, compression is good, ECU has been swapped out, coil pack has been swapped out. The missing is getting worse and now it wants to stall and actually stalled on the Interstate at 70 this morning. He has been able to find an intermittent no-signal from the injector drives on 2, and then 1 with the other ECU, but now he thinks it may happen to one or both sometimes as it misses worse sometimes than others. I'm starting think crank sensor. It briefly threw a code this morning but it came and went a few times, and of course, not when I got it to the shop.

 

Any better thoughts?

[White93z34]

has the ICM been changed?

[Galaxie500XL]

How old are the plug wires?  I'm betting they've been on there for awhile, right?

[primergray]

You might wanna try the old trick of popping the hood on a dark night, turning off the hood light, and see if you've got a lightning show with the plug wires.

[Nas Escobar]

Have you checked your IAC sensor? They can get carbon deposit and make the engine misfire.

[Nicutlass_Supremacy]

I had the same problem and I found that the IAC and all those conducts around it were filled with some kind of black rust. I´ve tried to clean it but I haven´t been succesful. I´m planning to buy a cleaner and some brushes to make a thorough clean.

[vipmiller803]

You are on the right path. Definitely sounds electrical. Crank or cam sensor could be suspects. ICM is also up there, along with connections to it. Poor grounds can increase in resistance with heat, enough to cause that. 

 

Since the issue is not isolated to idle, I would pretty much forget the IAC "sensor" (at the risk of sounding like a douche, I will correct it and say it is actually a motor).

 

Do you have the means to run tunerpro? That would likely feed you the problem on a silver platter.

[Nas Escobar]

 

Since the issue is not isolated to idle, I would pretty much forget the IAC "sensor" (at the risk of sounding like a douche, I will correct it and say it is actually a motor).

 

 

And it's marketed as a "Valve". The parts store lists it as "Idle Air Control Valve".

[GPX]

I appreciate all the feedback. My mechanic finally figured it out. While swapping the old ICM back in, he noticed a wiring harness had gotten loose, falling behind the motor and melting three wires on the manifold. These were occasionally shorting out, causing misfire. Heat shrink tubing and re-securing the harness have fixed it. Yay!