2001 Lexus rx300 misfire/ loss of power.

I am a novice with really no diagnostic tools. I have been part changing... I am at the end of what I can think of. The miss fire/ stumble under acceleration started after I fixed a cracked flex exhaust connection under the Lex. I have replaced all the plugs and coils, cleaned and tested the MAF. Cleaned the throttle body and replaced the IAC. The vehicle is running much stronger but still lack of power with quick acceleration and after the vehicle gets warmed up it seems the problem is worse. When in park their is no miss that I can detect. I am not sure what to do at this point. Help?

Do you have any way of checking fuel trims? These as with many toyotas suffer from blocked injectors which will show as positive trim numbers.

Seeing as how this happened after you fixed an exhaust leak, it is quite possible that you have an exhaust restriction. the vehicle could drive normally with the huge flex pipe leak, and then you fixed it and exhaust no longer had a way out.

I have no diagnostic tools. I am going to take this to a mechanic but want to know what i need to make sure he checks. I thought about the exhaust restriction, however the rpms do not raise when I experience the loss of power. . Also in the morning I do not seem to have the problem, I can push the pedal to the floor and have all the response one should get, after about 10-15 minutes of driving replicating the issue is as easy as trying to accelerate quickly. I had the codes checked at my local auto store. The history showed misfire in several cylinders, which I know before I changed the coils there were several bad. I had them clear the codes to see if they come back. I checked the MAF last night and when unplugged the vehicle dies, as it should.

Given limited info to work with it still sounds like a restriction. Follow along as I weave a possible scenario (something made up from the comfort of my chair).
Issue arose after fixing flex pipe.
Flex pipe usually a physical weak point in the exhaust chain.
Flex damage accelerated due to back pressure.
Back pressure is a leading cause of low power and stumble.

While driving to the local 7-Eleven, around 5:30pm on a Thursday, to get a Yoohoo, Slim-Jim, and Twinkies, you hit a pothole or something to jolt the 16 year old cat. The honey comb cracked and a section shifted out of alignment causing a severe blockage. The sudden pressure breaks the weak link and escapes out the crack so driveability didn't change much. Now YOU come along and fix the leak - removing the safety valve as it were - and all the exhaust pulses are back full force knocking the broken bits around. Meanwhile, the cat is expanding and contracting during heat cycles and when cold the broken bit is in alignment and flow is good. But when the cat is hot and expanded enough (say after 10-15 minutes), the broken bit can slide or is pushed out of alignment again and causing problems.
How's that for some Sherlockesque BS to tide you over?

I like it ! But I have an alternative scenario ! On the 16th of October when the Temps began to dip lower in the evening a lonely chipmunk climbed into the engine bay to escape the cooler evenings he took a nap in the air box where he Became entrapped! The next morning you started your vehicle and it was like hurricane force winds on that poor little guy who hung on for dear life for about 10 mins then was sacked into the intake tube and like a giant plug he became a huge restriction! Until you turned the engine off he was able to dislodge himself untill you fired the engine up again starting the whole process over ! Lol on a serious note I would get some live data on this car and see if this just happens to be when the vehicle switch from open to closed fuel loop...

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Yea, thanks guys..... Remind me not to ask serious questions on a site full of douche-bags.

Guys this website is about positivity and helping each other out. We all like a good joke but we do not tolerate disrespect or making fun of any of our members. Thank You.

You beat me to it Dylan this forum has an ethos of respect and learning so keep that in mind guys.

I sent JM1 a private message. I feel that the replies were intended to be helpful and they we misconstrued.

ScannerDanner wrote: I feel that the replies were intended to be helpful and they we misconstrued.

Agreed.