I have a 04 with 113k miles now. I installed some magnaflows a couple days ago which may contribute. But the problem started about a week now. My car no longer shifts smoothly from 1st to second gear, it also has to reach a higher mpg to shift to the next gear. There seems to be power loss whenever I start from a stop. I have the current mpg screen and it drops down to 7-8 whenever i baby it from a stoplight or stop sign. Another is that the down shifts i think from 5-1 arent smooth either. It would jerk from gear to gear. I can feel my car lunge when stopping. My car never did this before. I tried disconnecting the battery and reset ecu but it didnt help. I also tried to clean my maf as well. I recently cleaned my throttle body, maf and air filter not too long ago. My 90k service was done with plugs as well. I dont know how to diagnose this problem without a check engine light. Any insight? I want my baby back in top condition.

If all you changed were the mufflers I doubt this would the cause these symtoms. I would look more at the work done at your 90K service. Did you notice it right after the service? It is possible that a hard reset of the ECU will cause the car to re-learn driving style and shift points but this should take no longer then a week. Difficult to diagnose without any cel. Can you narrow down the symptoms to an exact time? Are you mashing her around town?

The problem arised about a week ago, before I installed the mufflers. My 90 k was done in November of 2013. It just recently started happening out of nowhere. I don't drive her hard at all. I'm try to save as much gas as possible

I'm a total amateur so I'd check all the easy stuff first, particularly air flow and connections on vacuum hoses. Check air filter and entire air intake assemble (plastic parts, clamps, hoses, electrical connects, etc) from filter to TB for any leaks or blockage. Check MAF for debris or loose connection. With recent work some hose or connector could be intermittently loose or have poor connection or have small crack, etc.

Has the issue happened on 1 tank of gas or does it span multiple tanks of gas? A tank of bad gas can make the car behave weirdly.

I am going to clean the maf, and throttle body again maybe tomorrow when I have time. That may be the problem, I filled gas last week on Thursday at sams. I use premium but maybe it was a bad batch of gas. I didn't even think of that. I am gonna try to waste all the gas with some spirited driving and fill up with some techron fuel system cleaner and dump some shell or chevron. Thanks. Hopefully this solves the problem. *crossing fingers*

was there a Transmission fluid change/check/top-off during that 90k Service? Also was it done @ Lexus?

The transmission has never been serviced before. I should probably do drain and fill. The 90k was done by my friend who is a lexus tech at my local lexus dealer using oem parts.

then it should be fine if it was never opened up. If you/he decides it needs servicing, he should know about this TSB already then if he's a Lexus Tech.

http://www.google.com/url?sa=t&rct=j...63738703,d.cWc

So an update, I was cleaning my maf, cleaning my air filter and took out the throttle body to clean again. To my surprise, two hoses were leaking coolant on the throttle body. I dont know if the throttle body is bad now or not. I went out to home depot and bought two clamps where you can tighten with a screw and hopefully that fixes the issue. When i took out the throttle body, I did notice some coolant around the opening of the intake manifold. Maybe coolant leaking inside is causing my problem. I cleaned up as much as I could. Lets hope I caught it early enough. I will be taking the car to school tomorrow and see if the response and mpg is better.

I have a similar problem on the non-Lexus car and I also tightened the hoses but I ordered replacement just to make sure that they don't explode down the line and leave me stranded.

when I had this problem I got a new battery and it fixed it


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Well, if he is leaking coolant on and in his throttle body he is definitely looking at the right place. Waiting for an update.

It seems as if my problem is now fixed. I guess age is taking its toll on the rubber hoses. My baby is now smooth like before and I also seemed to have gained 2 mpg according to the mpg calculator. I will check the throttle body again for any signs of leaking this weekend.

Another update, hopefully the last one. About a week from my last post, the symptoms came back. I was like WTF IS GOING ON?!?! So that weekend (4/12) I rechecked all my work and also went to advance auto to buy another throttle body gasket since it is still the original and I have taken off the throttle body a couple times already. Surprisingly the felpro gasket is made in Japan and looks identical to the oem. Anyway upon further inspection, the hose that connect from the pcv to the throttle body was cracked through a couple inches. It was hidden by the foam cover, so I didn't see it the first time. I put on the new throttle body gasket and bought a new hose to install. Been a little over a week and no returning symptoms. And my car shifts A LOT smoother, like how it supposed to be. No more jerking, power loss, or higher rpms to get going. So It either was the hose connecting the pcv to the throttle body or the new throttle body gasket that fixed my problem. Hopefully anyone else with these symptoms will kind of have an idea where to look.