My 2001, 150000 miles, Sub just started running a bit rough, possibly a misfire, but not sure? Around 45 to 50 mph, 1200 to 1500 rpm, most pronounced going uphill, engine seems to skip, run rough, misfire?, If i downshift it doesn't seem to do it? Normal idle and low speed, smooth running. There isn't any check engine light on. I thought about plugs and new wires, but some of the stuff I have read here doesn't really back that up as a solution. Possibly and O2 sensor although I thought I would get a check engine light for something.

Does anyone have any thoughts or recommendations before spending a $1000 with mechanic checking things of the list. Thanks in advance for any help!!

 

may be a pending code in the computer...scan to see.

 

2001, 150K miles I'd start with a good clean tune up...run a few bottles of injector cleaner, check the fuel pressure... clean up the MAF sensor...

 

Hook up a vacuum gauge and read THIS.

 

More pronounced going up hill... might be the catalyst stopped up.

 

My 2005 z71 does the same thing except hills don't seem to affect it

 

ummm yeah. you got clogged cats if you have zero vacuum....