My 99 xk8 has the same codes over and over restricted performance CEL on Ive checked every possible vacuum leak using maf spray and watching fuel trim levels. The car runs strong. I replaced the MAFS and the fuel pump and regulator are within specs. The o2 sensors check good. the vacuum hose to the EGR is good. Could the EGR be causing this? My mechanic thinks the control unit may be over sensitive is there a way to reduce the sensitivity? Ive checked every thread related to these codes p0171 and p0174 for ideas. I would appreciate any help.

Bill

 

I'd get more data. Engine hot, parked, watch fuel trims at idle then again when you rev to about 2500. Were they high and do they drop a lot? If they do you have an unfound leak. Also, are they similar bank to bank?

A $5 elm327 can do this....

 

Ok ill run that test today and post the results

 

The early XK8 did not have a egr valve. Make sure yours does. There would be a small pipe from the top of the right exhaust at the joint with the cat. Mine has a blanking plate there.
If you do have one common faults are a crack in that flex pipe or loose bolts holding the egr valve in.

 

+1 on the advice given so far.


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enjoy

 

Thanks sklimii, I wasn't paying close enough attention.

 

I ran the fuel trim tests and they did drop so we took the throttle body off and found the vacuum hose that connects to the bottom was split and also a crankcase vacuum hose was split. The fuel trims are good now and no vacuum leaks and no restrictive codes so far. Ill drive it awhile to be sure but it does look good. Thank you JagV8 so much.

Bill

 

Hey - good to hear it's fixed!