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95 4.6l still not running right

407 Views 1 Reply 2 Participants Last post by  General Zod
alright guys, here we go, i have a 95 tbird that i was getting some help on here for an injector problem. the problem now, is that i have replaced the injectors, edis, ecc, plugs, wires,and the MAF and i still have a rough idle that appears to clear up under throttle. it is not setting any codes. while viewing data on the scanner while the car is running it appears that two of the 02 sensors are not functioning properly. they very seldom read an input. could this cause my crappy idle. any other suggestions.
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if they are the sensors before the catalytic converters, then yes, they could cause a crappy idle, since those two are the ones the EEC uses to fine-tune the air/fuel mixture when in closed-loop operation........if the two sensors that came up are the ones after the cats, then you need not worry about those, as those are only used for monitoring catalyst operation

when you give it some throttle, it is quite possible that the bad idle clears up since at large throttle openings, the EEC switches to open-loop operation, and does not use oxygen sensor feedback to fine-tune the air/fuel ratio, rather it only goes by the MAF signal and some preset tables in the EEC.......if this is the case, then it means your O2s are switching slowly, but are still within the EEC's pre-determined acceptable limits

another possibility is a vacuum leak....when at idle, the air ingested thru a vacuum leak can be significant compared to what the engine normally ingests thru the maf.......but when you open the throttle, the air thru a vacuum leak is so small compared to the air coming thru the MAF, that it becomes insignificant and wreaks no havoc on the air/fuel ratio
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