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I Have A Predicament. Need Help!

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Alright where to begin... I have a 99 RX300 (AWD) that suddenly stopped running one day. Got it to start at certain times, with a really bad idle and would never stay on... Yes i've read the other posts on this problem, but i have tried almost everything. I am also familiar with the problems with the 1MZFE engine regarding oil sludging. Currently the car will start up, idle like crap and eventually want to turn off after a few minutes with excessive exhaust both front and back of vehicle (enough to push through exhaust manifold flange). DEF not driveable. This leads me to believe it may be the cat, but i figured i'd see if anyone here had any input first. Ran diagnostic with AUTO X-ray scan tool which popped a Throttle position sensor, but the check engine light wont come on. Before it was popping codes for misfires in cylinders 1,2,3 but changing out the cam sensors and OCV fixed that. I dont think there is an issue with the TPS that would make it have such excessive exhaust and seem like the car isnt breathing and idling like crap. The diagnostic tool displayed TPS at 2% with engine off and 10% with engine on at a rough idle. I suspect possible O2 sensor issues because they were intermittently showing readings but were not throwing codes...

Here is what I have done so far (All OEM parts from lexus):

Replaced fuel pump and filter

Replaced both cam position sensors

Replaced both Oil Control Valves (OCV)

Cleaned the hell out of the throttle body and Idle Air Control Valve

All new plugs and coils

Replaced valve cover gaskets

Checked and cleaned MAF sensor

Ran seafoam in gas

Changed oil (fresh)

Does anyone think it would be a catalytic converter issue or possibly the TPS or maybe something completely different? HELP!


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If you're pushing exhaust gas out of the exhause manifold gaskets, you surely must have an obstruction in the exhaust system. Short of someone stuffing a potato in the exhaust pipe, I'd certainly be looking hard at the catalytic converter. At that age, cat failure is not that uncommon although I have a 2000 RX300 AWD with 175,000 miles and still with the OEM catalytic converter. That's probably my next major expense. Let us know what you find.

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I agree with Filehorse. If you are pushing exhaust out of the flange on the manifold there is definitely restriction somewhere and (barring the potato), the cat would be the logical conclusion. Have you ever heard of a smoke test? They use it to test for restriction in the exhaust system. It introduces smoke into the intake (over simplification) and that smoke should exit the tail pipe. If there are ANY leaks of any kind, or restrictions, the smoke will come out of those places and reveal them easily. If there is not adaquate smoke coming from the tail pipe it would also be an indication of restriction, probably the cat, but COULD also be baffles in the muffler that have come loose and blocked the flow of exhaust. It takes a "smoke machine" to do this test. I think you've thrown too many parts at it already that it probably didn't need. It probably wouldn't have to be a Lexus dealer that did the smoke test. I would want to watch the teast, no matter who did it.

P.S. You want to watch what you put in the gas or intake. There are a lot of things that can potentially "poison" a cat. I am NOT a believer in Seafoam. I personally believe it's snake oil and wouldn't use it in anything I own, regardless of what the salesmen in the auto parts stores say.

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Alright to update the situation... I just disconnected the exhaust before the cat, and the smoke problem went away. But the idle is still very rough and stalls out after about 15-30 seconds. If i give it gas to keep it going, it tries to correct itself and idle right, but still runs rough. If i put it in drive, it stalls. If i put my foot on the brake, give it a little gas and then put it in drive i can move forward or in reverse as long as i dont let it stall out. Could the seafoam be doing this? I thought from day 1 there was bad gas, but i cyphoned it out and put 2 gallons of 93 in with a but of seafoam. I dont see what else would make it run this way...

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I've been reading more about the IACV... Does anyone think I should just replace this? I cleaned the hell out of it, but when i took it out it was so gunked up that the valve didnt even move. It was stuck in position. But once cleaned it seemed at ease. Any ideas?

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The IACV is very critical to that idle. Did you read the post carefully and get the washer etc back in the correct position.? Also change the pcv valve as that could cause excessive pressure and blowing of oil throughout the system. Replacing the IACV might be the fix, but maybe dissasembly and careful cleaning might be in order, with careful re-assembly. Make sure all of the vacuum lines are good also that are going to the cracked might cause problems.

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