I recently had to replace the engine in my 1979 Volvo 245. When I picked it up from the shop, I noticed that when I initially started the car, the idle RPM was a little rough. As I drove off and the engine warmed up, the new engine seemed to run very well and the car had better acceleration. However, after driving the car 3 1/2 hours back home on the interstate, when I stopped at a red light I noticed the engine idleing at 1700 RPM (normal is 900 RPM). Also, I noticed I was almost out of gas. Normally I get around 320 miles to the tank but now I'm only getting about 215 miles. After 2 weeks, the poor gas milage and high RPM problem continues. I've discussed this with the shop that installed the engine and they believe this problem is unrelated to their installation. I've asked a few guys at IPD if they had any insight into the problem. They think I may have a problem with an engine sensor or vaccuum line leak. I have checked the vaccuum lines and everything appears in good order. Does anyone else have additional insight and ideas on how I can trouble shoot and fix this problem? For example, I'm told by IPD that when a sensor fails the fuel systems defaults to full rich. Can anyone verify this, and tell me where the sensors are and how can I test them to see if there is a problem?

Also, I have noticed that the shop that did the engine installation failed to reattach the vertical metal tubular support from the block to the bottom side of the plenum (I'm not totally sure if that's the right name for it but I believe it's the air intake and distribution manifold). The rod is attached to the block but is not bolted to the bottom of the plenum. Could this be a problem?

And lastly...since I had the new engine installed, I discovered the negative wire from the alternator was not properly connected. The mechanic attached the wire and then loosely put the nut on the alternator negative post. He forgot to go back and tighten it down. The car did fine for a few days or so, then one morning it wouldn't start...the battery was at 8 volts. I jump started the car and tested the alternator and it tested good, 14 volts. I installed a new battery. Yesterday the car would not start with the new battery. This time I did a more thorough check and that's when I found the loose connector. My question is...could this in any way be related to my problem with poor fuel performance. I have noticed a slight decrease in idle RPM (now at about 1350 RPM, still high) or is this just a coincidence? (it's too early to determine if my gas milage has improved any).

Thanks in advance for any help!!