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1999 Es300 Hesitates When Warm Engine


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hey guys, im new to here and hope to be a participating member from here on out. I just purchased a 99 es300 with 150k on it, it has about 35k on a new motor replaced by lexus on this so called sludge issue.... when i bought it it had a p0303 stored in it and replaced the plugs... it did nothing then replaced the 3 coil, did nothing, i work at a shop so we ran 5 cans of toyota efi clean through the engine to try to unclog an injector... did not fix it. ended up replacing the 3 injector which fixed the stumble.. then checked compression on all 6 cyl, had 220 on all 6. ran it for a day and set codes for both afr sensor heater malfunctions and ciircuit response malfunction codes, 4 all together, at the same time. then i noticed a stumble in park when revving the engine, does it mostly about 30-45 seconds after a cold start, will not do it when engine is first started. i was able to use the toyota scanner to turn up injector rate 25% which cleared the strumble when revving in park.. my question is... can the afr sensors cause that stumble or are they mainly emissions sensors?? i would not rather replace them right now if i have another underlying problem at hand. any suggestions??

thanks in advance.


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I am guessing you mean A/F sensor. It iscalled that because it mean Air/Fuel sensor and can most certainly cause this problem. Most likey needs sensor replacement. Most likely tou have coated them in a bunch of crap with the over-use of the injector cleaner. I have yet to see a wiring problem with an O2 sensor, but I have only been in the field for so long.

There is a bunch of other crap I was going to add, but you are a technician and you know the ins and outs and tricks to the repair process.

good luck! Hope it works good after the replacement.

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