STSdriver Posted May 21, 2005 Report Share Posted May 21, 2005 I have a problem with an unstable idle, rough running at all speeds, and diminished power with my 1993 4.6 litre STS. I'm currently looking into two possible causes: Bad oxygen sensors: My car has 205,000 km (127,000 miles) on it, I've owned it for two years, and It's never run as roughly in the past. Could the oxygen sensors be defective? There have been no oxygen sensor trouble codes. I used the DIS to view the oxygen sensor voltage. PD32 is the front oxygen sensor voltage and PD33 is the rear oxygen sensor voltage. To get the DIS to display these, with the engine running, press OFF and WARM on the DIS and let the system step through its displays. When the computer asks PCM?, press the increase fan speed button. When the computer asks PCM DATA?, press the increase fan speed button again. Keep pressing this button until you see PD32 or PD33. You may now monitor the voltage and idle or drive your car. At idle, both PD32 and PD33 oscillate between 0.08 and 0.88 every 5 seconds. At faster RPM, the readings are the same and the oscillation speeds up with the RPM. After driving for 10 minutes, all these readings were the same. I am curious to know if these readings indicate the oxygen sensors are working normally? I looked into a few other possible causes: I checked the spark plugs and all were normal except #1 which was had a layer of black soot on it. I replaced this plug with no change in the rough running problem. Spark plug wires are all in good condition with resistances of between 1.23 and 1.40 kilo-ohms per foot. I replaced the fuel filter last summer. All my coils have been replaced in the past year (2 failed individually, and I replaced 2 trying to solve this rough running condition). The other cause I am looking into is dirty injectors. I took off the intake manifold cover and I checked the injector coil resistances. All coils had the same resistance. Everything looked fine, but I was surprised to see that there was gasoline pooled in the bottom of the intake manifold housing. Does this mean the injectors are leaking? I make two or four 5-10 minute trips to work during the week, so I wonder if these short trips can contribute to injector fouling. I just started to use premium fuel last month, I had been using the basic octane 87 fuel. Would having the injectors cleaned by a garage, using a cleaning product while operating the engine, do a reasonable job to clean out any fuel deposits? Is it a good idea to have them cleaned anyway, after 205,000 km? I read somewhere on this forum that there are instructions in the service manual for deactivating individual injectors, to see if there is a stuck or sticky injector. Would someone be so kind as to forward these instructions? I am interested in purchasing a service manual to help out with troubleshooting. I saw on another post that they were on sale for $30 earlier this year, but the price is back to $100. E-bay recently did not have a manual for sale for this car. Any other suggestions with this rough running problem would be much appreciated. I am hoping not to have to resort to the dealership - around here they charge $50 CDN just to look at the car using their instruments, and $99 per hour. Thanks for your advice, STSdriver Link to comment Share on other sites More sharing options...
This topic is now archived and is closed to further replies.