00 XJ, newly rebuilt short block and head, all new cooling system components, , plugs, etc.

It starts right up, idles fine when cold. After it warms up it idles around 500rpm when sitting at a stop light and in gear and seems kinda rough. No codes, but my tail pipe is black and after only 1000 miles on this oil change the oil looks like it has 5000 miles on it. Very dark, not black but a whole lot darker than you would think with practically all new parts.

Could this be a O2 sensor, injector, intake manifild gasket issue? The throttle body was thoroughly cleaned when I had it all apart doing the swap so I know it is clean. No oil in any of the lines for breather or PCV.

And I barely am getting 11mpg. Down from about 16 prior to swap.




Put my sticker on today!

 

Bah, stupid iPhone...

 

Really, No one?

 

My first thought was a leaking injector; if so (that would mean it's isolated to one cyl), that plug should look different. If it's something like an O2 or MAP sensor (also good possibilities), all cyls would be affected. The real strange thing to me is that you have no code set.

 

+1 to what belvedere said. I'd check the MAP, upstream O2s, and coolant temp sensor.

 

my guess is the coolant temp sensor

 

X2

 

Can you access a scanner that you can view live data?

You can watch the O2S long term and short term fuel trim activity while its running. A high (-) will indicate a rich mixture is being compensated for. If the PCM is pulling too much fuel off it may trigger a lean mixture DTC. You can also see if the O2S heaters are working by watching how long it takes for the O2S's to start working. The O2S's should cyle every 2 seconds. A cylinder burning coolant will show up as a rich mixture.

With my scanner I can check the engine coolant temp and inlet air temps before I start the engine. I found a bad inlet air temp sensor that way. A bad ECT sensor can be seen in the same manner. A bad ECT sensor should show up with odd temp readings on your instrument cluster though.

 

I don't have access to one I just have a small $59 one I picked up at AA. Ill go there and see if they can hook one up for a while.

The engine coolant temp sensor I believe is good, it is new from dealership. I am more inclined to think it is MAP or injector related. I pulled my plugs out about 2 weeks ago and they were all very dirty after only 500 miles. Here is a pic.



I do have one injector at C1 that has a crack on the side of it, but no gas smell or anything and it seems to fire ok. I am planning on replacing all of them as soon as I stash enough $$ for the 4 hole ones from Fuelinjectorconnection but I want to get everything else taken care of first.

I do have new NTK Up and Down stream O2 sensors from Rock Auto parts # NTK 23099 and NTK 23506. I plan on putting those in on Sunday and am hoping that will help a bit.

Is the MAP sensor tricky to swap out or is it pretty straight forward?

 

The MAP sensor is just 2 torx screws on the throttle body. Easy swap. Let us know how it runs after the new o2 sensors are in. Good call on getting NTK

 

They were cheap on Rockauto, $30 and $34. A lot cheaper than the dealership.

For the MAP sensor, can I get that at AA or AZ and be ok, or is there an OEM brand that I should get?

 

Ok I just ordered a MAP and IAC from AA, pick them up in an hour. I just ordered the injectors as well.

My birthday was Tues. and the wife got "me" a new shop-vac yet informed me that if I wanted to use a shop-vac for anything other than cleaning her car out I have to use the old one... So happy B-Day to me!

For the IAC, is there anything special about the swap out or is it a straight swap like the MAP?

 

Hit up Programbo on here, he does a nice job of refurbishing injectors and they're about half the cost of those ones you linked.

 

While you're dealing with your O2S's, check mini fuse F17 in the PDC. It's the O2S heaters relays power fuse.

 

Yes the IAC is just as simple as the MAP sensor. 2 torx screws. #25 torx screws if IIRC