rough idle

Discussion in 'Fox 5.0 Mustang Tech' started by Nibbie, Apr 9, 2008.


  1. Nibbie

    Nibbie New Member

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    ok for about a month now my car has been idling like crap. it pops and idles extreamly rough sometimes, especialy when it warms up. pulled codes (no check engine light on ever) always get 61-91, hego not switching, or o2s lean bank 1. I replaced both o2 sensors last week and im still having the same problem. checked fuel pressure today and its at 34 koeo (saposed to be 30-35 koeo) so thats ok, with it running its at 35 psi-so i know thats ok also. it wont stall or or turn off but it sure really uses a lot of gas, my fuel millage has gone down so bad and when i get on it somtimes it smells like gas bad. I also noticed my exhaust on the passenger side is a lot warmer then the one on the left (note-lean bank 1) im thinking thats why. I checked the o2 sensors wires/conectors today and they both seem to have voltage but im trying to figure out why they dont work. any suggestions? :shrug:
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  2. Bullitt347

    Bullitt347 man bewbs please...

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    When you get a code for O2 sensors, it does not mean that the sensor is bad, it means that the sensor is seeing something out of normal operating parameters, and the whole system should be looked at. A vacuum leak can cause a lean condition and make the O2 sensor go out of range. Once the computer tries to correct the lean condition beyond I think 18% (or rich by the same %) it will trip a code. The O2 sensor is just doing its job and letting you know that there is a problem. A dirty MAF sensor can cause O2 sensor codes as well. So can about a dozen other things, like bad catalytic converters, engine miss-fire ect. So you need to check the whole EEC system out to sometimes find the problem. Also a base engine concern can cause the EEC system to get out of sorts.
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  3. bloopbloob

    bloopbloob Member

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    what's your timing at? it seems a little weird that those are your only codes....
    symptoms sound a lot like the ones i had when my EGR valve went bad though...
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  4. Nibbie

    Nibbie New Member

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    i think the timing was set at 12degrees, today i got those two codes, the other day i got a maf code-out of range (forgot #) also coolant temp sensor out of range (forgot #) transmission temp sensor out of range (forgot #) and the two
    o2 sensor codes. (*i think that was because i ran the koer test and the car was not fully warm-codes never came back on 2nd test*) I think i should clean my maf sensor, havent done so in a while, also cleaned my egr the other day, looks and seems to work fine, also cleaned out my iac. checked for vacume leaks today and found none. now if its a bad cat could i eliminate the cat and go cat-less with an x-pipe and not have a problem?
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  5. bloopbloob

    bloopbloob Member

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    have you checked your timing yourself? i also think you should get your car up to operating temp, dump the codes then post them ALL, it will be a lot easier to try to get this figured out. also, you said you cleaned your egr, but have you checked to see if it holds vacuum like it should? mine looked fine, wasn't even dirty, but still didn't function properly. i think it had a tear in the diaphragm, but i couldn't see one....
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  6. mustangfan1990

    mustangfan1990 New Member

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    how do you know that one side is getting hotter than the other. Sounds like you might haev a intake gasket leak or something......anytime you get unmetered air coming in it is going to run lean. That said you could have something wrong with ur MAF sensor. Clean in like you said if that dont work I would try a new one
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  7. Nibbie

    Nibbie New Member

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    cleaned my maf today, wasnt really dirty. I still have the same problem, i didnt get to pull codes but i will do that tomarow again., wright them all down. I usualy run the test with the car at normal operating temp. oh and with my exhaust the passenger side gets about 10* degrees hotter then the driverside. It seems weird and i have never seen anything like that, the only thing i can think of is i have an exhaust leak somewhere for it to do that. I will also check the egr again. **(when 1st started up it runs smooth-after about 1 minute or 2 thats when it starts to run bad, i also think the hotter the temp outside the worse it gets**) :(
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  8. mustangfan1990

    mustangfan1990 New Member

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    Do you have cats on your car. I know if one is clogged your pipe would get hotter is the only thing I can think of
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  9. Nibbie

    Nibbie New Member

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    yeah i still got all 4 cats, yeah that may be why one exhaust pipe gets hotter than the other, also im considering just getting a summit racing x-pipe and just remove the cats.
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