'97 4.2L 188K miles bone stock. Every week or two, winter or summer, on a cold startup first thing in the morning, I will start the truck and it will run VERY rough. Worse than a 2 or 3 cylinder misfire. If I let it run, it will work its way out of it in 2 to 10 seconds, the IAC will have worked out to hold up the idle so there is a big flare in idle RPM but it comes right back down. Alternatively, if I immediately turn it off, and immediately start it again, it is always perfect. Truck has always run just fine except for a couple of these per month. It has been this way for 8 years, no change as it ages.

It isn't the IAC because it is working out to hold the idle speed up, the flare verifies this. I don't suspect a fueling or secondary problem or I would have one at other times. Does the CKP or CMP ever mistime on startup on these cars? That's kind of what it feels like. Ideas?

Thanks

 

With that mileage, have you replaced the spark plugs? Air filter? Fuel filter? What type of gas are you using? It could be that the fuel pump is bleeding down overnight and the first start up is a little lean. Try turning the key from off to run two to three times BEFORE you start it for the first time. If this helps, or fixes it, you could just continue the key ritual, or look into why the fuel pressure is bleeding down. That is another story.

Robbie

 

bigbronc, thanks. I posted this two places. Turns out there is a TSB dating to mid '97 for a new calibration. It happens so infrequently I probably won't bother to have it flashed. This must mean I'm still driving on 8 year old firmware.

Just for grins, I replaced the plugs at 105,000 and the wires and coil (older DIS style) at the same time to fix a misfire.