PLEASE HELP!!!! ABOUT TO GIVE UP!!!!

Hey guys/gals I am in desperate need of some help with my 1999 XJ. I keep throwing a CHK ENG light and have done everything I can think of to fix it. I have been getting the following codes:

P0122 TPS Low Voltage
P1694 No Bus Message Received from Companion Module
Bank 1 Lean

My gas mileage has plummeted and the Jeep seems to run and idle well from a cold start. Yesterday I was working on it and had the battery disconnected so the CHK ENG light was cleared, I drove 70 miles on the interstate today and it ran fine and seemed as though gas mileage was normal. I stopped for gas, then went directly to a drive thru and the light came back on and the Jeep started to idle rough. From that time my gas mileage again was horrible. I drove 90 miles and when I would come to a stop light the idle was very rough and was on the brink of almost stalling. When I arrived at my destination I ran the ODB2 reader and it showed the same codes as above. Any Ideas???????

I have recently upgraded the injectors but I do not think this has any possible relation to the issue. As far as what I have done to reconcile the issue are as follows:

-checked the wiring harness for shorts and have even replaced the factory splices
-checked and cleaned all grounds to engine and firewall
-replaced TPS
-replaced MAP
-cleaned IAC
-replaced PCM

I have a Firepower kit from Performance Distributors on the way in case it is coil related. Any chance this can even be related?

Could the CPS have anything to do with this?

Thanks for the help fellow XJers.....

You may want to start by testing the TPS. Here's a chart that shows the steps.

I use a safety pin as a back probe.


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That was the first thing I did when I started getting the symptoms. 0.8v at idle 4.04v at WOT. Power coming into sensor is 5.12v

is the P1694 from the TCU? could be that's defective or has a short and pulling down the tps votage?

where is the TCU located? I did replace the computer in the engine bay if thats what you are referring to.

On 97+ models the ecu and tcu are in the same computer. Earlier models 96- the ecu is under the hood, and tcu located under the passenger dash.

My 89 is idling the same way after doing injector upgrades, new exhaust manifold gasket, new vacuum harness, new down pipe. I don't know what to do either. It idles just fine before.

Mine is a 99' so I know its not the computer due to the fact I just replaced it, I did run across a post about the positive wire off the fuse box to battery could be to blame as simple as that is. Will be home on Wed so will buy new terminals and see what happens, fingers crossed.

Ended up being a loose positive wire from the fuse box to battery of all things...