Here's the problem in a nutshell.

'89 240 DL. Started 'stumbling' between 1800 and 2000 RPM under load, but only uphill. On the flat, you can gun the engine to your hearts content and accelerate like a rat up a drain pipe on fire without even the hint of a stumble.

If you shift up a gear to get the RPM under 1800 RPM, the stumble goes away, but then you eventually slow down to a crawl and have to down shift, at which point the vehicle stumbles again if you get to about 1800 RPM and you lose power.

None of this happens on the flat or down hill, only up hill and decreasing the throttle doesn't stop the stumble until the RPM drops below 1800. The problem is getting progressively worse.

I'm thinking, in this order:

Dirty fuel filter, bad electrical connection, bad low pressure fuel pump or possibly throttle position switch.

Anyone ever hear of this problem before?

 

fuel delivery would be high on my list of things to check. when my in-tank pump went out, and the car was under 1/2 tank of fuel, it would starve and stumble under heavy throttle at upper mid RPMs in 2nd or 3rd (automatic). new in tank pump, and varooom.

See In the Tank - 240 Volvo Tank Pump and Sender for ways to diagnose this...

 

That was my suspicion (In tank fuel pump). Oh, joy. ;D