Hi all, having problems in cruise control mode.

1996 Volvo 850 Turbo Wagon - Automatic - Engine Type 57 - 2.3 L - 127,000 miles

Lately with Cruise Control I am getting an RPM surge between 300 and 500+ RPM at random times even when the CC switch is ON and NOT engaged. Getting surges when running under CC also. At a stop with foot on brake it sometimes surges like that and is quite frankly pretty scary.

This does NOT happen when I turn off the CC switch. Only when it is on. No surges with the CC switch in the off position.

Any idea's where to troubleshoot this? Any help would be greatly appreciated.

Thanks in advance,

Clark

 

I'd think there's a few possible causes - there may be an issue with one of the speed sensors (sensor/reluctor rings etc) or you may have a fuel trim issue - MAF/fuel pressure/spark etc. You didnt mention any CEL codes or idle issues so I don't think its an intake air leak. Quite often spark issues can appear like a fuel trim issue - when was the last time the car had a full stage 0 tune - ie wires/plugs/cap/rotor? Any other symptoms - ie warm start issues etc?

 

thanks mt, I don't have any surges when the CC button is turned off on the stalk. Only when the switch is in the on position.

When it's in the On position it does it randomly. The only codes I have been pulling are the P0131 and P0137 codes which I believe is bad O2 sensors which I have been trying to isolate. I have had those codes for a few years without any CC problems.

This doesn't seem to fit your scenario. What do you think?

Thanks again,
Clark

 

I think the two could be connected. the front O2 sensor has a heating element and a sensor so its likely your fuel trim is slightly off which under load can turn into a misfire. The rear o2 sensor is there to monitor the catalytic converter and if its bad it won't really impact the engine's performance (but may indicate an issue like a clogged cat which could impact the engine). I'd start by replacing the front o2 sensor. If you want to save a few bucks you can buy a generic "splice in" sensor vs the 850 specific sensor where the harness is specific to the car. You should find the connectors on the firewall.

 

UPDATE:

I replaced the Cruise Control relay with one I salvaged a few years ago. So FAR it seems to be working correctly now. Still more tests in the works but no surging so far.
Thanks,
Clark