850 surge on Crusing speed

nitink · Post by **nitink** » 15 Jul 2006, 15:03

My volvo's cup of woes seems to be overflowing by day

My 850 surges badly on cursing speeds

, higher the speed more it surge and its progressively getting worst.

Also I notices if I am driving under 40mph its fine and as speed increases surge also increase..

I have newer spark plugs, fuel filter, air filter, oil filter, new rear breaks, , (5K Miles). new clean flame trap (150 miles)
Distributor cap & Rotor are about 3 yrs old but have only 12K miles on them.
Wires from distributor to spark plugs are about 5 yrs old.
I tried to locate vacuum leak but couldn

Post by **robert213** » 15 Jul 2006, 21:13

Usually surging results from ECU with mismatched injectors or sensors. Could previous owner have replaced with larger than original injectors?

Check Diag Trouble Codes for clues.

Check fuel pressure at shrader valve on fuel rail. Possible problems with fuel pump. Still, I would replace main fuel filter.

Possible bad O2 sensor.

Possible bad Mass Air Flow sensor.

nitink · Post by **nitink** » 16 Jul 2006, 02:21

Thanks robert
I cleaned MAF & its connector after hearing from you. MAF Connectors had slight white liquid on them. cleaned MAF & Connector with a dry paper towel. Car runs better now, but not perfect. I think if I should clean MAF with some commertial cleaner.

I don't think injectors were ever replaced. They are dirty as hell, I have to put a bottle of injector cleaner every month to keep it running.

How can I Check fuel pressure? and what is shrader valve on fuel rail ?

>> Possible bad O2 sensor.

Wouldn't it set any code? its a possibility as this car is suffering from poor and quite up/down gas milage.