1995 Es 300 Spark Plug Replacement Issue

tsquare · July 30, 2013

I own a 1995 Lexus ES 300 with 110,000 miles and am located in Northern New Jersey. Recently I replaced all six spark plugs and all six plastic coil connector clips, which is the first time that these items have been replaced on my car. I used NGK OEM Iridium spark plugs from Autozone and OEM connector clips. After finishing the job, the car started OK the first few times but ran extremely rough and would not rev beyond about 3,000 RPM. After successfully starting it 3-4 times, it now will not start up at all. I have rechecked all of my electrical connectors and air hose connections, reset the on-board computer by unpligging the battery, and found no error codes on my OBD II reader. Wouild one bad plug/coil/connecotor set prevent the car from starting up? If so, is there any easy way to diagnose which plug/coil pair is causing my issue? If dirt or grease had accidentally gotten into my air intake manfold or throttle housing, could that be causing my start-up and rough engine issue?

Any suggestions on how to further troublseshoot and isolate my exact problem would be greatly appreciated. Thanks in advance for your guidance!

tsquare · August 3, 2013

I'ver spent much time over the last few days trying to diagnose and fix my problem without success. I have removed and thoroughly cleaned the throttle body and IAC Valve with Throttle Body Cleaner (both were very dirty with visible carbon build-up and had never been cleaned before). Also, I cleaned my MAF sensor with Electrical Cleaner. I also replaced my fuel filter, since it had never been replaced by the previous owner. I've also checked all of my hoses and gasket connections for air leaks. Currently, the car will start (although it takes 3-4 seconds in time) and it idles smothly at about 900-1000 RPM. However, the car experiences sluggish acceleration (especially in lower gears and and when driving up hills. In higher gears it seems to run better but still experiences some sluiggishness. After driving the car locally for about 35 miles, I am only getting a single error code: P0170 - Fuel Trim Malfunction (Bank 1). Also, I replaced my Rear Manifold O2 Sensor about 2 years ago, so I don't think that is the problem. According to the online reading that I have done, MAF Sensor failures in 1995 ES300 modles are realtively rare, so I tend to think that also is not my problem. Also, I don't think it is a transmission issue, since that system wasn't touched in any of my recent repair work. Could a dirty or failed EGR Valve cause this type of issue, or could a leak in my exhaust system be the root cause? I am starting to run out of ideas of things to check, so any suggestions on how to further troubleshoot would be greatly appreciated.

tsquare · October 31, 2013

I wanted to provide a follw-up post regarding my original problem. I took my car to a local MIdas dealer, who told me that I needed to replace my MAF sensor, which I did, but that did not fix my problem. Midas then diagnosed low fuel pressure (2 psi) at my new fuel filter port and told me that I needed to replace my fuel pump, which I did, but that still did not fix my problem. I then gave up on Midas and took my car to my local Lexus dealership for more diagnosis. After three hours of diagnostic time, they determined that my fuel pressure regulator (FPR) had failed (due to human error - the air intake nozzle had become bent and thereby damaged the internal components in my FPR. Interestingly, my FPR passed 4 of the 5 diagnostic tests that Lexus had performed on it. They ended up removing the FPR and then saw via visual inspection that the FPR was physically damaged. Also, I was getting no black smoke out of my exhaust system (typical when an FPR fails), and FPRs rarely fail on mid-90's Lexus and Toyotya models, so this was definmitely an extremely rare failure mode. Just glad that my problem is finally fixed! The FPR is extremely easy to remove, so it is well worth your time to visually inspect it when you are trouibleshooting your fuel system.