Help! still struggling with this 1990 740 wagon, rex regina sys. B230F 2.3L auto. 165K miles. I get a 1-2-2 code which means air temp sensor. Where is it located, I looked in the airbox but nothing there, haynes is little help as they don't feature much on the RR system. I originally thought the 1-2-2 code was the MAP sensor but I think I was reading the code diagnosis list wrong here. Also getting a 3-2-1 which is cold start valve, it says the problem source is the radio relay, is there any fix or test I can do with this? Idle is very rough, the whole car shakes when cold. Engine smoothens out at speed but still oscillates, so its still rough but higher rpm is smoothing it over. Runs strong otherwise. Also, how difficult is it to replace front wheel bearings?

You can take the cover off of the radio suppression relay in order to check it for dry soldered joints, which you can then re-solder. It might be easier just to buy a replacement ;) I have no idea about the air temp sensor, though; I think that most (if not all) 740s sold here had Bosch fuel injection. I've never changed wheel bearings, but apparently they are fairly easy to do... Good luck :)

Front Wheel Bearing 

Front wheel bearings are straight forward to change. The bearings come already assembled to the replacement hub and I wouldn't bother trying to change just the bearings unless you have loads of time and suitable equipment. Remove the brake caliper, the caliper mounting bracket and the brake disk. The hub is held on by a large hub nut which is very tight. I used a breaker bar, a good quality socket and a length of scaffolding pole. Once the nut is off then the whole hub / bearing assembly can be pulled off by hand. Reassembly is in reverse order, as they say but the new hub should come with a new nut which needs to be torqued to 74 lbf ft and then angle tightened 45 deg. I think there are three types of hub: Pre '88 (I think the brake disk is part of the hub) and two post '88 types which will be either for ABS or non-ABS brakes. The ABS sensor ring being part of the hub. Bought my hub through fleabay and changed it in under an hour in the street, including dragging tools from garage, making tea etc. etc.

Hi Jonesg , Sorry to hear you're still having problems. Would have thought the air temp sensor would be in the air trunking leading to the air filter. Look for a connector with wiring coming off it. Maybe its been broken off though at some time. Have a look underneath as well as above the trunking for any sign of where it might be fitted.

Thank you 

Thanx guys, I've been busy and getting busier with work, xmas catering. By coincidence I just met the guy who owned the car from new, he's doing plumbing for my landlord right now and asked how I liked the car etc. I asked 'when was the timing belt changed', he says "oh we never did any of that, its all original". He's a character.! So its got almost 170K on the timing belt already. Sensors aside...for right now...I'll get back to that.. Is it safe to say the rough idle is due to timing being way off ?, I don't have a timing light but it doesn't take a rocket scientist to see this car is basically solid yet seriously lacking some mechanical upkeep. I ought to change the water pump too right? Damn winter, it gets serious here in Boston. Thank you kindly.