Thought I'd throw this out there to see if anyone else would know what this is.

I have a 97 5.9 wired to a 98 PCM in my Wrangler. Been trying to track poor fuel mileage for awhile, and been noticing a rough idle after a starting it after it's sat a bit (still warm).

It'll idle rough and a bit low, and a intake hiss/whoosh will accompany it. It'll smooth out when I rev and usually won't come back into a rough idle. But if I leave it idle it seems to load up on fuel and get lower rpm.

It has a newer TPS and idle/air control.

My 5.2 truck did the whooshing thing after I did the water pump and intake gasket if I remember right, but I don't think it ran rough.

Any ideas?

 

Where is the pre-cat O2 sensor located in the exhaust now? How old is it? What sensors did you use?

 

I'm using a modified Dakota y-pipe, so it's in the stock location at the Y. Newer Bosch sensor within the past year or two (only 4000 miles on it maybe). Secondary is right after a small Magnaflow spun cat.

One thing I've been wondering is if there are differences between the sensor ranges between 97 and 98. It's a 97 harness and sensors with 98 PCM. I doubt it, but I've always wondered.

 

There's the problem right there. Not going to guarantee anything, but I suggest you try an OEM or get an NTK o2 sensor. And go from there.

 

Put in a NTK sensor today. I can't imagine the Bosch sensor not doing well, being using them for years in my Jeeps. But for $40 it can't hurt to try I guess...

 

I did a search here yesterday on Bosch o2 sensors for the hell of it. And you would not believe how many different models of dodges don't like them. I thought it was just our Rams.

 

What kind of issues are they supposed to be causing? Just low MPG?

 

All the usual things associated with incorrect mixture ratio, including running rough.

 

+1..... I'm telling you, put "bosch o2 sensor" in the search box and read some of the threads. Any of them, doesn't have to be 2nd gen rams. You'll be amazed. I was.

 

YA I did a lot of research also and made me refund my money haha