I have a 1999 Lexus RX300, Check Engine light is on, and I've being experiencing the following symptoms from it. In the mornings when the engine is cold, and I drive beyond 2000 RPM, the vehicle jerks, almost like its coughing, but the very moment the temperature gauge begin to move beyond the C mark, the vehicle runs Perfect All day, but then this happens all over again the following morning, but only if i go beyond 2000 RPM with the engine cold, otherwise it runs smoothly, aside from the slight engine spudder/miss felt in the steering. So far I’ve changed All spark plugs, All ignition coils, all the O2 sensors, MAF sensor, IACV, timing belt, water pump, Coolant temperature Sensor and even the Engine computer. Someone please Help me!!! The vehicle has 125 thousand miles on it. If ANYONE has a solution to this problem, you can email me at alexcambridge@hotmail.com. Thanks for any assistance...

Please give us your codes.

Hi,

Thanks for your quick response. I will go into auto zone this afternoon and have a diagnostics ran, and will post the codes.

Hello Lenore,

I just got back from Auto Zone, and unfortunately they were unable to retrieve any codes from my RX 300.

Something strange here. Are you sure you have a check engine light on? I have never heard of a CEL that didn't produce any codes. Why didn't Autozone reset the CEL light while they had the scanner plugged in? Assuming all that is correct, I would suggest disconnecting the negative battery cable for a few minutes to reset the ECU. Then drive and see if your CEL comes back on. If so get the codes read again.
Also you have changed a lot of parts. Did you always have the CEL and did you change the parts to try and solve it? Or did you cause the CEL somewhere along the way while changing all these parts. It just sounds like a lot of guessing at parts changing without getting a code read which will tell you what part to change.
Is it definetly the engine you are feeling or is it the trans trying to shift but failing to do so? When cold the ECU raises your shift points slightly, this is normal but the sputtering is not.

Hello Mikey00,

I've read many post and comments on the net, which mentioned how the trans in this vehicle tend to be faulty, however, I'm happy to say that I've had this vehicle for a little over 7 years and haven't had any transmission problems. Unfortunately I've had to resort to throwing parts at it with hopes of resolving this issue. In addition, when i changed the O2 sensors, they had in fact corrected some issues I had experienced.

The CEL came on a couple of months ago, and sadly I've been unable to get it to go away; obviously because i have not been able to figure out what is wrong with it. The timing belt, and water pump were changed out primarily for preventative maintenance reasons. After changing the ECU, i noticed a slight positive change with respect to the idling, but its still not a clean as i know it should be. Can anyone please advise as to whether or not my 99 RX 300 has a EGR valve, as I've read where people had similar symptoms as I do, and it turned out to be a faulty or clogged EGR valve?

I would concentrate on the CEL and trying to properly get the codes rather than continuing to throw parts at the problem. You must have lot of money spent on parts by now.
I see you are in the Bahamas. Is is safe to assume Auto Zone knows what they are doing when it comes to reading codes? If not find anyone with a scanner or by one for about $50.

At this point i guess it may be cheaper for me to purchase a scanner. This is the second time I've had it scanned and both times I was told that it didn't give any codes.

There are very basic OBDII readers available on Amazon and ebay for about $40. This should be a lot cheaper than throwing parts at the problem. The ECU alone should have been over $1000.
I didn't think it was possible to have a CEL without a code. So I question the reading of the code even though it is a simple process. Maybe someone else knows of a situation I am unaware of where you can have a CEL without a code. There's nothing you are leaving out like you bought a used ECU and the CEL came on after it was installed or anything like that?
You may want to try the battery disconnect I suggested above to reset the CEL.

Hello Mikey00,

Unfortunately the CEL showed up when the original ECU was installed, and then I then I purchased a used ECU and installed it, and i noticed a slight improvement in the idling, but several minutes after installing the ECU i purchased, the CEL showed up again. I have also attempted to reset the CEL by removing the negative battery cable, however; roughly 30 minutes or so later, the CEL returned.

You pretty much eliminated the ECU. And with the CEL returning after a battery disconnect It's not just a one time thing. I still say there has to be a code in there. Is there anyplace else you can try and have the code read?
There are so many things this could be like your new timing belt could be off a tooth, if your replacement sensors were not Denso, that sometimes causes a problem, etc. But all this is shooting in the dark without the code.

You gotta get the code it's throwing (don't clear it) I suspect a bad coil since the code comes back after 30 seconds (typical of a faulty coil) but you want the code to know which one. And a faulty coil would give the hesitation as mentioned. If all that isn't fruitful, I'd probably reinstall the old ecu, just to see if it acts the same....

Here is an interesting cheap code reader that Costco just started selling for $35.

Click to view attachment

In my opinion, very important... no aftermarket parts for me! Also, I wouldn't own a late model car in these days without have a scanner. Best money you'll ever spend!

Hello all,

Thanks for all your contributions. I found a nice scan tool on ebay, however; its not yet in my posession. As far as my original query, the jury is still out on that, and i'm tired of pulling my hair out over this issue, so i have taken my rx 300 back to my mechanic of 7 years and basically threaten him within 2 inches of his life, lol, and reminded him of the fact that i had paid to have this issue resolved but the vehicle was returned to me without resolution. That said, its been at the mechanic shop for 2 days, and they have no resolution to this matter as yet. I will keep you all posted on any developments. This is such a pain in the butt.

Hello all,

I just wanted to give an update on my issue. Unfortunately i am still seeking a resolution to this issue. I was able to purchase a very nice OB2 reader, but sadly i got the same results my mechanic, the folks at Auto Zone, and a friend of mines go, which was Nothing! The scanner showed that the malfunction indicator was on, however, it indicated that there were node codes. I even tested my new scanner on two other cars what had the check engine light illuminated, and it gave the codes immediately in both cases.

Now, after this unsuccessful attempt, i took my Rx 300 back to my mechanic and after almost 2 weeks, he was only able to tell me that he suspects that the problem is originating from coolant temperature sensor. He does not suspect that the sensor itself is bad, as i myself changed that several weeks ago, but he suspects that the underlying cause to my problems may be an electrical issue. I've had to take my RX 300 back from my mechanic as i had pretty much depleted a great deal of my funds on a rental car. In the interim, I will continue to do on-line research, and in a week or so, i will take it back to my mechanic for further investigations. Again, if there is anyone that can offer some insight into this issue, and a possible resolution, Please,Please do not hesitate to do so.

Could something have been left disconnected that would trigger CEL but not have a link to show a code?