Hey guys I have a 98 discovery 3 years and 30-40k miles only few issues have happened. Now this year I keep getting couple codes and running issues. First one middle muffler broke off mount so i had it fixed. I get p0420 started running rough so I replaced exhaust last weekend and just cleared code today. I just bought an obd2 scanner because of issues best purchase so far. The other code p1178 code couple times. What it started to do is misfire and run rough after warming up. Doesn't idle right unless I rev it up for second before driving. So what I have done lately clean MAF, new filter, iac replaced from high idle issue that I still have when i first cold start. New plugs, wires, temp sensor, crank sensor and wire from other issues had year ago. Fuel filter at last oil change check vacuum lines. So I haven't changed MAF or done anything with intake gaskets Any test for those. I have 170k on it now I only paid $100 for it 3 years ago and now have $1800 into it with all repair after I replace power steering hoses this weekend. Any info would be great guys thanks

 

OK, a couple of things first... Welcome to the board. Always good to have new people. There is a specific D1 section so future threads should be posted there. Also, to prevent having to specify which truck you have, it is best to put that info in your signature. Find the 'user CP' section and edit your signature there.

Now onto the problems... p0420 is a "Catalyst Efficiency Low Fault Bank A". When you say you replaced the exhaust, did that include the catalytic converters? If not, I suspect your driver's side cat is on its way out. The p1178 "Maximum Positive AMFR Correction Fault", very likely to also be related to the cats.

Cats for these trucks are fairly expensive so I'd try new upstream O2 sensors first. If you wind up having to put in new cats, you'd probably want new O2 sensors anyway.

O2's can be had at Amazon for ~$55. Look for NTK 250044.

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