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A friend of mines 1998 S10 2.2L truck started idleing rough just the other day it has around 135,000 miles on it no major issues that I know or he had the 02 sensors and cat replaced about a year ago. I told him I would ask on here to see if I could find the most likely problem he is not very mechanical and we work very different scheduales so im trying to keep the diagnosis parts as simple as possible Thanks in advance for everyones help.
Forgot to add that he had it scanned and it came up with a p0705 p0301 and p0420
the p0301 is a misfire the 705 is a transaxle sensor and the 420 is a fuel mixture issue I believe.
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P0420 is a cat code. Aftermarket cats dont last very long in comparison to OEM replacements. I would see if that is still under warranty.
Do you have a scan tool that shows PID data? The post cat o2 sensor voltage should be a steady 0.45v. If its fluctuating, you have either a bad cat, exhaust leak or misfire.
For the cylinder #1 misfire, have you completed any basic testing yet such as checking for spark or fuel to that cylinder along with vacuum leaks?
For the P0705, you ‘may’ have an issue with your PRNDL switch. You would need to consult a wiring diagram and a troubleshooting flow chart for that particular code on that particular vehicle.
I havent looked at it yet I’m going to look at it this weekend I just wanted to get some ideas before I do Im mainly concerned with the misfire cause that seems to be the only one effecting the car Im leaning towards it being a vaccum leak cause the problem only shows at idle and not while driving. do you know if the misfire would be what is causing the P0420 code because the fuel air mixture is off?
Thank you for your help
It’s possible the misfire caused the P0420 but I would focus on the misfire cause first. It’s not likely the P0420 has anything to do with the O2 sensors, it’s more likely you have a bad cat. As for the misfires look to the tune up stuff first, plugs wires, and also check for vacuum leaks.
You can use the above videos for that. Good luck and keep us posted.
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