rough idle and rough or no start when warm
 

Hello everyone. For the last month I've been having some problems with my '99 S70 automatic non-turbo. Once it gets warmed up the idle will drop when pulling up to stops and then go back up to normal after a second or two, but it feels like it is almost going to stall before it does that. Then if I shut the car down I have to wait about an hour or more sometimes before I can get it to turn over again. It will crank but it will be really hard to start. Usually I can get it if I give it a little gas but recently it seems like it's getting even worse with wanting to start. These problems also seem to be tied to the weather outside as they seem to get worse when it is under 20 degrees F. I pulled the codes a while ago and got some related to the O2 sensor, so I replaced the upstream with a denso sensor. It seems to run a little bit better now but I am still having the rough idle and hard starts when warm. I pulled the codes again and the only ones in the system now and all I get is P0328 and P1057 "Manufacturer control" which I'm not sure what that means. Any advice is greatly appreciated as this is my only car and it has become very annoying to deal with like this. Thank you!

start by clearing the codes and see what resets. the P0328 is referencing a knock sensor - but that can get triggered by the misfires or it can point to a bad connection to the sensor etc. The P1057 is not a standard code so if you google it you may get different answers as to the reason. I did see one that suggested it may be an intake air temp sensor but didnt see any similar references. May be best to get a dealer to scan with VIDA

Ok, first and foremost, as mentioned, clear the codes and see what comes back. Secondly, the to main things that come to mind to me a re a weak fuel pump / fuel pump relay, or a failing intake temp sensor. This sensor is located right under the thermostat in the same housing and sends the engine temperature to the dashboard gauge as well as the engine computer. If it is failing, it will send an erroneous temp signal to the computer and the computer will then either lean or richen the fuel mixture based on the incorrect signal the sensor is sending it. This will cause the engine to idle and run poorly. A tip....... at the first start of the day (after sitting overnight, see what the temp gauge is reading before you start it. I once had a sensor that would cause the temp gauge to read as it would with a normally warmed up motor when the motor was stone cold. Car ran like crap until it actually warmed up.

Thanks for the advice so far guys. I'm going to clear the codes and check the temp gauge when I start it today. Ill report back any new info.

Any updates??