I have been having a problem with a cold start stutter and misfire. I get 1-4 codes telling me there is a misfire issue. The freeze frame data tells me that the ECT(Engine Coolant Temp) sensor and the IAT(Idle Air Temp) sensor are reading 419 degrees. The wires are testing out properly when the car is running while using a scanner to test the wires unplugged, unplugged and bridged, and plugged in.

I have checked for loose wires and grounds and I cant find any anywhere.

I also seem to be burning coolant and having pressure in the system somewhere as well. I don't know if the problems can be related or not, but something is going on. I would like to make this engine last forever, so I need to figure this out somehow.

I have checked for hydrocarbons in the coolant with a hydrocarbon test machine and it came up with 25 with a max of 100. So the test is telling me that the head gasket is fine.

I don't know if this issue of stuttering is an ECU/PCM problem or not. I cant imagine it is because of the tests I have done.

Also, the plugs are not switched because the car has run fine for years without an issue and it just started a couple months ago. I have never unplugged them before, so there is no way they are just switched.



*maybe an unrelated issue here, I am getting the code P0420 for Catalytic Efficiency Below Threshold(bank 1).

I assume that is the pre-cat o2 sensor. I have replaced the cat a long time ago after the old one was clogged. I have swapped the o2 sensors and I still get the same code, so it must be an outside source causing it. Once I clear the code with my code reader, the emissions status on the code reader still show a yellow light as if there is still an issue with the entire emissions status.

I don't know if any of this is related or not, but I need help!!!

Should also know that I have changed the cap and rotor, the distributor is functioning fine according to tests I have performed with it torn apart, the spark plugs have been changed, and the fuel pump and filter have been changed.