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Hi I have a 1999 R170 that shows up two fault codes, P0170 Fuel trim bank 1 and P0303 cylinder three misfire. I swapped no. 3 plug with no. 1 but still got the same result. The strange thing is the car runs and idles quite smoothly with no sign of a misfire. Can anyone suggest where to look next and what the P0170 code means?
 

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Hi I have a 1999 R170 that shows up two fault codes, P0170 Fuel trim bank 1 and P0303 cylinder three misfire. I swapped no. 3 plug with no. 1 but still got the same result. The strange thing is the car runs and idles quite smoothly with no sign of a misfire. Can anyone suggest where to look next and what the P0170 code means?
You swapped the plug or you swapped the coil pack? The coil pack is what you want to swap.

See http://www.obd-codes.com/p0170
 
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Thanks for the info. I cleaned the MAF last week before I ran any checks. The car is fine on light throttle but if I drive it hard it runs very lumpy on idle. Maybe I need to replace the MAF? This morning I swapped the coil packs over and the P0303 code cleared (misfire on 3) But shouldn't I have seen a fault on another cylinder? and also checked for vacuum leaks, all ok.
 

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You might want to change the MAF , cleaning doesn't always work , I've even heard of new , non OEM ones , not fixing the problem !
 

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Thanks for the info. I cleaned the MAF last week before I ran any checks. The car is fine on light throttle but if I drive it hard it runs very lumpy on idle. Maybe I need to replace the MAF? This morning I swapped the coil packs over and the P0303 code cleared (misfire on 3) But shouldn't I have seen a fault on another cylinder? and also checked for vacuum leaks, all ok.
I'd wait a bit to see if the P0303 code reappears. Certainly wouldn't replace anything until it does. As for the P0170 that often is a MAF issue. If you do decide to replace it, please read some posts about using a real Bosch MAF vs. some of the aftermarket junk that's out there.
 
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