Please help I have been working on this thing for a while my 1999 Lexus RX 300 is stuttering from about 2200 rpm’s to about 3000 only once a gets warm it does it and if you were fully end of the throttle it doesn’t do it at all either I have change the spaijrk plugs cleaned a bunch of the sensors as well as check the fuel injectors no codes are coming up no check engine light is there anybody out there that might be able to help please either give me a call at(916) 917-0144 or e-mail me at rawb1584@yahoo.com my name isRobbie and I thank you very much for your time and hope to hear something soon I have to go to work out of town Monday!!
Ps. The car does have 250000+ miles on it but has been well maintained and did run very well (other than lack of power) up until this point and I did stop driving immediately and took to the mechanics but he is having a hard time diagnosing the problem!!!

 

Maybe the timing is off? Have you checked for any codes recently?

 

Emission related problem will light up there CEL [includes, knock sensor, misfire etc]. If the CEL is lit up, have the codes read. Confirm the bulb is working, by nothing its light up when you move the ignition key from ACC to RUN (step before the start)

Salim

 

Yes it works but no it’s not on or has never came on yet at least it would make this a lot easier!!

 

Assuming no one has tampered with wiring, you dont have misfires and you dont have knock sensor problems.

How about quality of fuel and air filter condition?

Salim

 

i did replace the air cleaner less than 1k miles and don’t think that could be the issue unless it further down the air intake system? I know that the O2 sensor reading on two of them matched but the third was about 1k more than the other two but the mechanic said that’s beacuse that’s the one behind the catalytic converters? I was thinking more like the vvt system like the timing valve solenoid filter or maybe even something to do with the cam gears? I am stumped but won’t give up until I can get it fixed!!!

 

ask the mechanic to check the fuel pressure and flow rate.
Next would be live data monitoring.

Salim

 

Thank you all for all of your input and all of your help!! After many many long days of wrenching we have finally solved the problem! And it runs great! To start we cleaned all the sensors (MAF,throttle position,vvt sylenoid oil filter,O2 sensors,and every other one we could!!) changed the oil and filter, ran the sea foam top end cleaner through the top end, cleaned the boots for the spark plugs and checked and cleaned the connection prongs, changed the spark plugs (NGK iradium) the mechanic said that was a whole lot of fun he had to loosen the top end then lift it up about 2 inches and that gave him just enough room to get the boot to clear when you pull it off the spark plugs on the back side the on that is right in front of that little hole is easy but the other 2 are very difficult to get to (unless someone left the wiring harness in bolted so you have the room) without removing or raising it. It says you can on you tube I know but you try it and you will see what I’m talking about!! We reset the ECU, changed the air filter, and just made sure everything was plugged in good and wasn’t cracking to much around the wires and put dielectric grease on some of them, cleaned the terminals, and checked the rest of the fluids. We started up and it spun like a top!! There is still a slight vibration when it shifts sometimes and we figured out that it is the front knuckle on the drive shaft and when we looked at it the boot was blown out and there was some play in the fitting at the knuckle in front so tomorrow or within the next few days I get to go get a new one (luckily I found one for $200 instead of $750!!) and put that in (which looks pretty easy! Or I hope?) and do the breaks and then my baby will be all better and there will be nothing wrong with her once again!! She runs so much better and so smooth when it shifts and I got all the power I was missing back and then some plus I’m sure I am now getting much better gas mileage(TBD)!!!! I again thank you all and if I can help anyone please feel free to ask!!

 

Rawb1584,

What is the part number of the knuckle you are replacing?

 

also, OP, you did not mention if it was over heating or not ???? If it is over heating (needle over the middle mark) then I am fairly certain you have a blown head gasket.