Working on a 98 S70 T5 manual trans, I've had for awhile now. It's got me stumped. Under light acceleration and while driving at a steady speed the car will sometimes begin hesitating, almost like the igniton is cutting out then just as fast as it started it will stop again. It is throwing no codes. Everything I've seen on here and other forums that seems close to my problem either acts up under hard acceleration or it will also have idling and stalling problems. My car has neither problem, if you put your foot to the floor it won't miss a beat, likewise, it has never stalled. It won't even miss a beat at idle if you clutch while the car is hesitating at let the engine drop to idle, it will just purr like nothings wrong. So what could be causing behavior like that? I have done all the routine things that I've seen recommended because I did have an occasional missfire when I first got the car. I've replaced the plugs (NGK), wires (Bosch), dist cap/rotor (Bosch), coil, cleaned the throttle body (which is still the non electronic/cable style), checked throttle position sensor with scan tool, cleaned MAF sensor and rerouted and strapped the cable to the MAF sensor per an old service bulletin I found. I've got no codes, but it still hesitates and shudders randomly. Any ideas?

 

The key word here is RANDOMLY. It's likely the fuel pump relay. That should be a time change item, every 10 years.