Coolant gauge reading low... rough idle.. 4.0

Ok.. This is on a 1994 ZJ 4.0. I know that this is an XJ forum (I have an Xj as well), but it is a probelm on teh 4.0 engine, so it is very similar.

Any ways.. first problem. The coolant gauge reads low. really low. I had the dealer verify that the engine was heating up with the DRB machine. It was.. at the time it was at 190*, but the gauge was only 1/8 of the way up (the gauge is in teh same increments as on the XJ). I replaced the sender twice. tested the sender as well. This is the sender on teh back of the head. I checked teh wire going to the gauge for continuty and avoltage drop and it was found good. I also swapped out the orginal gauge cluster for a used one and the same thing happens. I also checked teh plugs becaus eif it was actually reading that low the plugs would show it. And they looked good. The gas mileage is fine as well.

Any ideas? I am stumped on this one.

Also it runs rough at idle after it heats up. The engine mounts are good, replaced the tranny mount. Did a full tune up not to long ago (plugs, wires, dis cap, dis rotor, air filter). I also took off the TB and cleaned it and the IAC. This is only at idle that it runs rough. I was thinking maybe the TPS?

-Chris

Sounds dumb check ground strap to engine. Are any other gauges doing something strange?

No, the rest of the gauges are fine. As for the ground strap... I just checked that and I can't find it... and Idea where it should be on a ZJ??

-Chris

ground strap should be attached in the back of the engine near where the guage sending unit is.. it loops around a studded head bolt and attaches to the firewall. If it isnt there, make one. Also make a good battery to body ground.