Hi fellow members. I'm kinda frustrated. I have a 2003 LS with 138,xxx miles. Just yesterday i pulled into the gas station turned ignition off, got back in, and when i started her up the check engine light came on. I thought that was odd but continued to back out and get on the road. Immediately i noticed that the rpms were way too high, even just rolling at 5mph was over 2500. Got onto the main road and as i accelerated up to 65 the rpms never went under 3500 and also it didnt shift into fourth until I had to let off of the gas and hit the gas again. It continued to do this since. Same thing today too, except the check engine light turned off. Temperature is fine, no change in performance from cold to hot. Checked fluid levels, nothing extreme. It is killing my gas mileage. 2 months ago i had a new thermostat put in which solved previous shift issues, not the same issues as this though. Also, let me put in mind that the past few days here(minnesota) it has been below zero degrees. Im trying to include as many details that could relate, to my knowledge, to my problem. Any help would be great, thanks everyone in advance.

*forgot* i did just add a bottle of STP Fuel Injector & Carburetor Treatment to this round of gas, not for any particular reason, simply because it has been on my shelf for awhile and figured might as well, related? i dont know

 

First step would be to pull the trouble code that caused the check engine light to come on. It will still be stored in the computer even thought the light is out. That may lead you to a solution.

 

Get the code read. I would check the cat

 

Next time it doesn't shift, let off the gas and put it back on again, it might shift after that.

Get that code checked out. Could be the P0420 that is so common

 

just looked it up for you it is catalyst system, low effciency bank one. might be the cat and one of the sensors or both sensors or all three items i would go what is a little more easy on the pocet as in the sensors first if the code ond the problem comes up again it is the cat

 

thanks guys, im thinking its time for a new cat, starting with sensors. Its been showing all the symptoms before including harsh shifts, i knew i would need to sooner or later. When this sprung up i didnt know if it was also related or something new.