high RPMs in Park

[CJ's30]

Hi, great site. I have searched the site for this topic. I own a '97 J30 that due to Firestone's mechanic error threw a timing belt and locked the engine. I didn't know it was mechanic error until I had paid American Engine Installations to replace my engine with one they bought used from Japan. What a nightmare. Could have had Firestone pay to send to Infinity if I had know it was a mechanic error. Too late. The original engine had 112k miles and the used says 50k. AEI took all my parts from old engine and put on the new used engine. I (supposedly) paid to have a NEW water pump, entire gasket set, manifold gasket set, front and rear seals,new timing belt and sensor, new radiator, temp sending unit, themostat, fan clutch, oil sending unit and new hoses put on. It took the fight of my life and checking and rechecking the mechanic, but I didn't have much choice 'cause by the time they showed me that it was Firestone's fault, my engine was in 1000 pieces all over the shop floor. Firestone, by the way, was fabulous. It took 3 tries but the car is home and doing well EXCEPT that in Park, the RPM's run at 1250. In drive they settle in nicely at 950. My gas milege has gone from 310 miles a tank to 250 a tank. I have taken immaculate care of my J30. She is my Darling. I have done all required maintenance and changed oil every 3000 miles. Any suggestions? or should I be happy that she's home safe and sound? Thanks. Also, on another topic, is there a difference between a Service and Repair Manual which I have and a FSM that you refer to in the posting instuctions? The FSM sounds more detailed and I'd be interested in obtaining one. Thanks again

[driverdriver]

Welcome to NICO!!!

Do you let your J warm-up?

When I start up my J, the RPM's shoot to around 2000 and gradually settle down, hitting 1300rpms and then settling to around 1000rpms. This is normal.

As a rule, I let the car warm up till I see the temperature needle start to tick.

[95-J30tt]

i would guess that it is the Throttle Position Sensor (TPS).... not adjusted correctly and it could do what you mensioned, but it would also cause a harsh and incorrect gear changes....

the way to check for it is to get an ohm meter, and to follow the FSM on the correct voltage at fully closed throttle (from what i remember, it should be around 0.5 volts, but please double check).... i hope this helps, good luck