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Car Forum / Lexus Cars / July 2005Engine runs rough above 40 mph
I have a 1991 Lexus es250 126000 mile engine that runs rough above 40 mph for a while, then runs smooth, then runs rough. Mechanics tuned it up and replaced spark plugs,ignition wires, distributor, rotor, air flow meter, air filter, alternator belt. None of which solved the problem. Thanks for any suggestions. See if there are any codes stored in the computer, could be a sensor.  SignatureEd Smith"I came into the world with nothing and I still have most of it" >I have a 1991 Lexus es250 126000 mile engine that runs rough above 40 mph > for a while, then runs smooth, then runs rough. Mechanics tuned it up and > replaced spark plugs,ignition wires, distributor, rotor, air flow meter, > air filter, alternator belt. None of which solved the problem. Thanks for > any suggestions. There are no codes stored >I have a 1991 Lexus es250 126000 mile engine that runs rough above 40 mph > for a while, then runs smooth, then runs rough. Mechanics tuned it up and > replaced spark plugs,ignition wires, distributor, rotor, air flow meter, > air filter, alternator belt. None of which solved the problem. Thanks for > any suggestions. internally broken exhaust, esp. cat converter, may give those symptoms. have you had the fuel filter changed, again that is a possibility. mrcheerful Check engine light came on today when I got to 55 mph. It was codes 25 and 26. According to the manual, codes 25,26 have the following in common;engine ground bolt loose,open or short in injector circuit, fuel line pressure,open or short in oxygen sensor circuit,oxygen sensor,water temp sensor,foreign object caught in valve, and ECU. What would be the most likely cause? > Check engine light came on today when I got to 55 mph. It was codes > 25 and 26. According to the manual, codes 25,26 have the following in > common;engine ground bolt loose,open or short in injector circuit, fuel > line pressure,open or short in oxygen sensor circuit,oxygen sensor,water > temp sensor,foreign object caught in valve, and ECU. > What would be the most likely cause? Most likely causes are oxygen sensor and loose ground bolt/poor connection to ground. SignatureRay O correct the return address punctuation to reply I ordered an O2 sensor for $67.00. With 126000 miles I guess it needs to be replaced good or bad. Hopefully this is the problem. Thanks for your suggestion. >I ordered an O2 sensor for $67.00. With 126000 miles I guess it needs to be > replaced good or bad. Hopefully this is the problem. Thanks for your > suggestion. To clarify, I doubt if the O2 sensor would cause the engine to run rough but it cold solve the check engine light. SignatureRay O correct the return address punctuation to reply >> Check engine light came on today when I got to 55 mph. It was codes >> 25 and 26. According to the manual, codes 25,26 have the following in [quoted text clipped - 5 lines] >Most likely causes are oxygen sensor and loose ground bolt/poor connection >to ground. also your mass airflow sensor...probably with that mileage, it's dirty. >>> Check engine light came on today when I got to 55 mph. It was >>> codes [quoted text clipped - 9 lines] > also your mass airflow sensor...probably with that mileage, it's > dirty. Good point! SignatureRay O correct the return address punctuation to reply The air intake sensor was replaced with the air flow meter. Also about 10 months ago the fuel pump,fuel filter and gas tank were replaced.The gas tank had rusted and clogged the fuel lines. The gas tank was replaced with a used gas tank. > The air intake sensor was replaced with the air flow meter. Also about 10 > months ago the fuel pump,fuel filter and gas tank were replaced.The gas > tank had rusted and clogged the fuel lines. The gas tank was replaced with > a used gas tank. I forget what type of vehicle you have, but an air intake sensor serves the same purpose as an air flow meter. I doubt if your car has both. Are the ignition wires and spark plugs OEM parts or aftermarket parts? SignatureRay O correct the return address punctuation to reply A mechanic installed the wires, they have Japanese letters on them.I was going to replace them myself until I saw I would have to remove the air intake chamber to get to the 3 in the back. Looking at the manual for my 1991 Lexus ES250 page FI-37, the air flow meter has an air temp sensor built into it. The O2 sensor should arrive today so I'll see if it fixes the problem. Also could the PCV valve cause this problem? >A mechanic installed the wires, they have Japanese letters on them.I was > going to replace them myself until I saw I would have to remove the air > intake chamber to get to the 3 in the back. Looking at the manual for my > 1991 Lexus ES250 page FI-37, the air flow meter has an air temp sensor > built into it. The O2 sensor should arrive today so I'll see if it fixes > the problem. Also could the PCV valve cause this problem? Genuine Toyota/Lexus ignition wires will say Toyota or Lexus or Nippon Denso or ND. Come to think of it, I don't think genuine Toyota/Lexus wires have Japanese writing on them. I'm not sure why, but Toyota/Lexus seem to run poorly on aftermarket ignition parts - plugs, wires, rotor, etc. Many of these kinds of driveability problems are solved by installing OEM ignition parts. I suspect that what you think are Japanese letters are actually Chinese. Many of the 8,000 characters are identical in Japanese and Chinese so someone who cannot read either language would have a very difficult time telling the 2 apart. I thought you had called it an air flow sensor, not an air temperature sensor. A bad air temperature sensor is unlikely to cause the drivability problems you are describing. I doubt if replacing the O2 sensor or PCV valve will solve the problem. I'd start with genuine Toyota or Lexus ignition wires and plugs, cap, and rotor. Also, make sure that the base ignition timing is correct and that it is advancing correctly. SignatureRay O correct the return address punctuation to reply > I doubt if replacing the O2 sensor or PCV valve will solve the problem. I'd My Lexus LS 400 1994 had the same symptoms. I replaced the PCV and changed the air filter. No improvements. I had two faulty O2 sensors, ignition wires and plugs replaced by the official Lexus shop using official parts. The engine seemed to run rougher below 1500 rpm than before, but had no problems above 75 km/h as it used to. I guess the O2 sensors were the most important factor in the improvement. However, gas consumption went up from 13 l / 100 km to around 14.5 l / 100 km when the "repair" was done. Now, after about 6 months and 5000 km, the symptoms are back. Car runs a bit rough above 60-75 km/h. Next, I am planning to replace the throttle position sensor (or actually swap the "unused" TPS from the ESP with the normal throttle TPS). Is this a good idea? Emissions measurements (3rd party) were fine before and after the repair. If someone knows the proper fix for this, I would be very pleased to hear about it. I wrote earlier: > Next, I am planning to replace the throttle position sensor (or actually > swap the "unused" TPS from the ESP with the normal throttle TPS). Is > this a good idea? The TPS in the normal throttle and the sub-throttle TPS were slightly different. The resistance over the normal TPS (Part# 89452-33010) is 4.2 kOhm over the resistor, while sub-throttle (Part# 89452-55020) has a resistance of 5 kOhm. Most likely I could have changed these and adjust the angular position of the potentiometer to find the right engine behavior. However, I soaked the two TPS devices in CRC 5-56 (contact aerosol) to reduce the possible noise created by the potentiometer inside. Once I installed them back, the slight roughness in engine in speeds of 60-90 km/h or so was gone. The measurements over the 1-2 and 1-3 pins were according to manufacturer specifications before and after soaking both the TPS in the contact spray. The roughness is easily explained by the bad contact in the potentiometer. Often, old integrated amplifiers share this behavior: the potentiometer starts creating noise. In the TPS, the noise is sensed by the engine computer as the driver (or traction control) constantly varying the throttle position, and the fuel injection system tries to compensate by pushing too much or too little fuel into the engine. This results in less than optimal smoothness. Both of my TPS dated mid 1993 (my LS is an early 1994). If you do not have traction control, you have only a single TPS to worry about. It is very difficult to diagnose this problem properly, since replacing the O2 sensors (and parts of the ignition) hide the symptoms for a while. Also, the guidance in the factory repair manuals do not give proper instructions on how to find out a worn TPS. The TPS has to be really seriously broken before the factory repair manual instructions will detect it as faulty. Summary: If your lexus runs slightly rough when driving about 75 km/h, repair or replace your throttle position sensors first. I replaced the throttle position sensor , but the problem still exists. I got under the car to replace the O2 sensor and noticed that something had leaked onto the O2 sensor wires. So, I decided to wait on replacing the O2 sensor until the leak was fixed. I took the car to a mechanic to figure out what was leaking. He said it was the power steering pump and gave me a price to replace the pump. I decided to wait a couple of months to save up to pay for it. I was hoping the leak onto the O2 wire was the problem. The power steering pump has been replaced( $210 for the pump and $325 for 4 hours labor which for some reason took 7 hours). I decided to wait to replace the O2 until the weekend. I noticed that the abs light now comes on after driving the car a few miles. I checked the code(31) and it means either front right wheel; 1.speed sensor, 2.Sensor rotor or 3.wire harness. I looked at the repair manual and it looks like something I can replace or repair myself at the same time I replace the O2 sensor. The nuts on the O2 sensor are extremely rusted on. I was wondering if the Speed Sensor could have anything to do with the rough engine since it might be easier to replace. |
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