I am not sure if yours is like my 740, but on mine, I had this problem, and it ended up being my RSR (radio suppresion relay). I swapped it with the Aux fan relay right next to it, connected to the overflow tank. It worked fine.

I didn't have that problem, until I replaced my head gasket a couple of years later. Now the 740 sits, but I drive it about 5 miles every two weeks, for circulation.

Kevin

1990 740GL Rex 216K
1997 960 126K

I used to have that exact model year. mine was that nice metallic dark grey.
I recently parted her out and sent the carcass to the junkyard.


Mine picked up a number of werid hard-to-diagnose problems before I quite driving it. Mine would actually sputter, loose power, and backfire several times before it started to drive properly. I never really got it solved, but in retrospect, I strongly suspect that the injector temperature sensor was telling the car it was cold, so it was continuously dumping too much fuel into the system

My FPR also went all wonky at one point and the ECU ramped up the main pump until it hissed and buzzed. This ended with the car flooding out and dying rather far from home.

btw: have you checked your throttlebody lately?
--
1967 P220 Amazon, 1972 145S, 1976 245 DL, 1983 245 DL, 1986 745 GLE, 1990 745 GL, 1995 945....
You mean to tell me that Volvo makes cars that are *NOT* Wagons?!?
1971 P1800E... Not a wagon, but it's just a donor car for the Amazon..

Consider that you could have a significant vacuum leak. The FI system may adapt to it when warmed up*, but the sudden acceleration shoots in slug of extra air (which is all the "gas pedal" provides) makes the already lean mixture too lean to run smoothly.

*When cold, the extra fuel provided by the ECU for cold running could be "masking" the false air sneaking in unreported by the AMM.

I use Propane to test for vacuum leaks. It's less messy—and no more volatile— than carb cleaner or other sprays. Take the nozzle tip off a propane torch and replace it with some snug fitting rubber hose about 2 feet long. Practice with the valve to get a moderate gas flow (not a roaring blast).

With the engine at a warm idle, open the gas valve and poke the end of the hose around each injector for a couple of seconds. If the seals leak, you should hear an RPM change when the propane gets sucked in and burned**.

Do the same around any other suspected areas, like hidden vacuum hose ends — and don't forget the intake manifold gasket itself.

To block the breeze from the (240) fan, lay a piece of cardboard from the fan shroud to the engine

**If you use a Digital Volt Meter to "read" the O2 sensor output voltage (O2 signal wire disconnected from ECU), you'll see the signal voltage rise instantly if any propane gets drawn in.

--
Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Bare with me... does the non turbo have a hose going over the top of the engine to the PVC valve? If so... pull this hose off, make sure it isn't clogged. I recommend this because my car had the same problem once... it took me quite sometime before I found the source of the problem.

Best Regards,
Anastasia

Cover the basics before sinking the money into computers. Does this have the original wiring harness? Know issue that can cause lots of symptoms.

Had the same problem on my '89 turbo. Turned out to be the ignition wires. I had replaced them also but purchased a cheaper "standard connection" brand that was designed to make contact with the walls of the distributor socket holes. The Volvo distributor has posts in the holes as contacts. The standard wires never touch the posts and creat an additional gap that the spark voltage has to jump before it reaches the plugs. This weakens the spark and causes missfires. If you don't have the proper wires I would suggest replacement.