First post ever on this forum! I'm very excited. I've been on JeepForum when I had a Wrangler and IFSJA.org when I had a Grand Wagoneer. Glad to be here with my XJ.

Ok here we go...1999 XJ Sport 4.0L. This morning I am driving it and simultaneously the gas guage drops from 3/4 full to E and the Check Engine light comes on. So I ran over to Autozone and had them run the Code. It was the IAC module so I bought a new one and put it in. Then things got silly.

After installing the new IAC my engine varied idle between 3000-4000 rpms. It will go down to 2000 then shoot back up. It shifts gears hard and has trouble breaking because the idle is so fast. The gas guage goes from E to Full, then back again, and the Check Engine light is still on. Basically it's a party.

I unplugged the battery for about an hour, plugged it back in. For about a minute it seemed things were normal, then it went crazy. I thought maybe it just had to reset itself so I drove it a couple miles at 45 mph. No joy. I unplugged the wires from the back of it and plugged them back in. No joy.


HELP.

 

Update: I took the new IAC Module off and put the old one back on and my idle issues were gone. I still had no fuel guage and a check engine light. I returned the part and got one from a different store...same issue, so I returned that one also.

As it stands I have a code saying Idle Air System, and no fuel guage. Help or I go to the mechanic in the morning!

 

It would be helpful if you could get the actual code. I'm not saying that idiotzone's code reader is NFG, but try O'reilly or Advance auto to get the code(s) read.

 

X2 on the code. A lot of times the codes mean that there is a problem within the problematic circuit which doesnt mean its the exact part. My TPS for instance gave me a CL light and so i replaced it and the problems continued. Try following the wiring harness to and from the CPS and see if there is a bad spot.

 

I had it read at advance also. The code says Idle Air system. What else would cause this?

 

What is the NUMBER of the code. You are telling us the interpretation - not the code.

Clean BOTH battery cables!

Reset the computer by disconnecting it at least 8 hours. Less than that does nothing.

See if the gauges work or the code comes back.

 

When you installed the new IAC did you reset your computer by disconnecting your battery and letting it sit for a minute before reconnecting it? If not I would give the new IAC another shot.

 

I did disconnect my battery for about 2 hours before re-trying the new IAC. I ended up taking it this morning to a mechanic I trust.

His conclusion: The ECM needs to be replaced. He said the dealer part was very expensive, I should buy a programmed one online and put it in myself.

Apparently the fuel circuit in the ECM is open and stuck that way. So I ordered the refab unit from Autozone, should be here Thursday.