Gentlemen,

New situation here. I am looking through the FAQ but would appreciate any additional insights in this specific situation. Engine starts and runs, including restarting when warm. Temporarily, I am using the electric fan relay in place of the apparently defective radio suppression relay. The car is a 1990 745 T, automatic transmission, 202,000 mi., new NGK BPR6ES spark plugs, new spark plug wires and air filter.

The engine, however, until it has run for a couple of minutes, wants to stall, that is, the engine, left to run by itself with the driver's foot off the gas, will drop down to zero engine speed and the engine stops running - with the gear selector in park or neutral. The same engine, at the same time, will idle by itself, albeit at a high - for this car - rpm of 1100 if the car is in any gear. Engine idle with the transmission selector in gear like this is also smooth. But shifting into park or neutral returns the engine to needing careful gas pedal input to keep running.

Then after a couple of minutes of running, the engine idles by itself even in park and neutral, but at a high idle of about 1300 to 1400 rpm and with pulsating changes in rpm. The pulses were at about one second intervals and then, a minute or two later, the intervals were getting reduced to something like half a second. It sounded like the engine was gulping for air or gas. The air filter is new and the air box below the filter is clean and open at both ends. I did recently find the idle air control valve frozen nearly shut. I took it off the car then, stood it on end, sprayed a lot of WD 40 into it and left it that way overnight. The next day the shutter was opening and closing freely. That is the idle air control valve that is on the car now.

A current fuel pump check using a jumper wire to bridge the terminals on the relay board that match the fuel relay spades of 30 and 87/2 indicates that both the fuel pumps are running. The intake fuel pump sound that is audible at the gas filler neck also disappears and reappears with withdrawal and reinsertion of fuse No. 11 during that jumpered state. Please let me add here that tests a few days ago with the fuel line output going into a measured can suggested that the pre-pump in the tank was not adding to the amount of gas being pumped through the fuel system. Is it possible for the pre-pump in the tank to be running, but clogged up? Could this be causing or contributing to the pulsating idle in park and neutral?

By the way, my fuel pumps start running as soon as I jumper those terminals, even without the key in the ignition. Anything wrong with that? I have the impression from the FAQ discussion at -Fuel System: Pumps, Relays- that the jumpered pumps there start running only after that ignition key is turned to on (II ? ).
Note about the electric fan and radio suppression relays. The innards on my two relays look the same, although 10 X magnification indicates slight circular cracks around some of the solder points on the non-working radio suppression relay. Is that all it takes to render the relay defective? Geez, my car is 18 years old and full of electrical connections. Please let me add here that it is my conviction that the Volvo 740 turbos are probably the pinnacle of automotive passenger car engineering. I will do what it takes to keep driving this car. Thank you.