OK, this might be a long one so please bear with me. Background:
-'98 XJ Sport, stock, ~120k miles, kept outdoors since day 1
-been experiencing O2-type issues (rough idle, throttle drop followed by a 'pop', check engine light occasionally comes on with O2 sensor codes)

Now, here's the story. I'd had bad sensors in the past, so I was pretty sure this is what was going on. Took it into a mechanic for service, and they replaced the sensors (and in the process, mounts apparently rusted away and they had to put in a new cat/exhaust).

Well, after dropping them a check for an embarrassingly high amount of money, the Jeep wasn't in any better shape. I took it right back. They replaced the spark plugs, gave it back to me, no dice. They then outsourced to another shop, who decided it was the engine computer. They swapped in junk parts, didn't work, ordered a refurbished computer, got it programmed, same issue. The two shops then put heads together and decided one or both of the new sensors must be bad (my first suggestion, btw). They supposedly replaced them again, and gave it back to me.

That brings us to yesterday, and so I take it back out on the road. First thing that happens? Stalls while sitting at a light. Next run out later in the evening? Throttle drop and pop. Same issues.

I'm going nuts - Of course, I'm assuming they've actually done all the work they've claimed. Is it possible there's another issue here? Or should I just take the keys and go elsewhere? I really don't want to drop more money into a 13-year-old car, but I also don't want to drive it with an issue this big. Any help, advice, or insight is GREATLY appreciated.

 

Check CPS, TPS, IAC, any and all fuel and spark components.

 

Thanks for the quick response. I'm not really sure what any of that means or how to check them, so what's the clearest way to approach the shop about this?

Side note, noticed the Wantage location tag. Go Sussex County, grew up there myself. Hamburg. Small world, lots of XJs.

 

Find the CPS connection terminal, put a DMM across port B and C, should read inifinite resistance. If not replace it. Clean IAC and TPS with carb cleaner.

Go figure, Grew up in Sparta, Moved to wantage about 3 years ago. Lots of XJs haha

 

What happens if you just unplug the O2 sensors? Just curious. I had an O2 sensor problem on my Wrangler, but it cleared when I replaced it. But until I replaced it, I just unplugged it so it would quit acting up.

 

Downstream o2 has no effect on performance, it will just trip a cel.

First one plays a role in fuel/air and constantly checks the emissions.

 

Thanks for the suggestion, I actually had both O2 sensors replaced. After they did all sorts of other work, they decided it must have been a defective replacement part. Supposedly, they've since swapped in two new sensors, but it's still acting up in the same manner.

I guess my next step is to head over and see if they'll do Diesel's suggestions.

 

Well, I took it in, dropped the suggestions on them, and ultimately they're just throwing in the towel. So I guess I spent $1k on O2 sensors and cat+exhaust and am no better off.

CEL lit back up last night, too, and the guy says it's indicating the sensors again. If I take it to someone else, is it possible the CPS, TPS, or IAC being out of whack would cause a false alarm CEL on the O2 sensors?