Check Engine Light On Again. Help!

[mike brown]

i bought a 1996 gs 300 with 121500 miles on wednesday night. before we got about 20 miles away (bought ift from a person i know that sells cars on the side) the check engine light came on. took it to the dealer and they scaned it for free. needed one of the up front o2 sensors ($280 installed - sound fair?). when ahead and did it because the car seemed to run rough. seller offered to pay 1/2. got it back thursday afternoon and took it for an oil change.

friday afternoon the light came on again. it sometimes idles rough and has a little bit of shutter at about 45 mph when accelarating. other times it runs ok, seems to be rougher when engine is cold.

i took it to autozone for a free scan today and the code was PO305 - misfire on #5 cyclinder. auto zone thinks it may be a plug, plug wire or cap. cap and wires look pretty good from the outside. do you think this is all that's wrong? culd it be anything major that would warrant me taking the car back and asking for a refund?

should i take it back to the dealer, use a lexus cert. local shop auto zone suggested that i heard good things about or elsewhere? according to lexus it had a plug (readout did not say plugs) changed at 80k. should they just change the one plug or do a complete tuneup if that's it. how much should a complete tune up run?

thanks, mike

[TurboGS300]

There are 3 02 sensors all should be replaced at the same time and if the cap, rotor, and plug wires have never ben changed they should be done as well. Replacing one item is not really the way to go, you should replace things as a set. <_< I look at it this way any lexus you buy with that mileage is probably goig to need all the items I mentioned. Hey, you're also going to need to repalce the timing belt like right now, if it hasn't been done already. B)

[cruznroadking]

Mike, When the check engine light comes on it could be several different things. If the spark plugs were replaced at 80,000 miles I would suspect the spark plug wires are not firing properly. Average life of plug wires are 100-150,000 miles. The only way to determine if the spark plugs need replacement is to remove & inspect the wear on the center electrode. If the electrode is rounded & worn & black & sooty looking it's time to replace them. LOL

[mitymouse]

I'd be pretty upset with the person that sold you the car. Chances are that he disconnected the battery and reset the engine light for your test drive. It usually takes 30-60 miles before the light comes back on, even though the problems are immediate. A shifty dealer did the same thing to me and I got home, 70 miles from the dealer and it came on. Turned out to be a $750 charcoal canister and the dealer says tough cookie. More of an answer to your question -I know the 2nd gen GS has over 70 sensors that can set off the light and yours probably has close to the same. Your plugs should definitely be changed if they haven't yet. And the timing belt. Wires are probably ok but might as well change them to be sure. The 96 has a rotor cap??? My 99 has seperate coils for each cylinder.

[mike brown]

I'd be pretty upset with the person that sold you the car. 

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i bought the car from an old family friend and he offered to pay half without me even saying anything. says it never came on before so i'd prefer to believe him than not, although it is sort of strange. after taking it back to lexus and talking to a few lexus local shops, i think somebody has pressure washed the motor at one time and it may have water on #5. took it Monday and lexus dealship cleared the codes. they suggested plugs and wires. hasn't missed or come back on since, so i'll bide my time for now. btw, the lexus dealership wanted $400 for plugs/wires. talked to a brother-in-law of a guy i work with that is a retired lexus tech (and a wealth of info). he suggested 2 techs he used to work with that formed their own shop and specilize in lexus. they qouted me a price of $264.

thanks for the replys.