My mysterious surging and rough idling problems were successfully resolved last night. Everything was very simple. In fact it was so simple that I feel a little embarrassed. Thanks to Warren who put me on the right track with his questioning my recent maintenance efforts. From that point I went back to the events of last Sunday and tried to trace back everything that I did. Here is the story.

Last Sunday I decided to clean the throttle body and the flame trap on my wife’s S90. This was not the first time for me: I performed this procedure several times on my previous Volvo car, ’86 744Ti. Everything seemed obvious. I disconnected the big black intake hose from the AMM, IAC and TB. Also, to get better access to the clamps and hoses, I removed the plastic black cover that covers throttle pulley and throttle spindle. I then cleaned TB without disassembling it. I had hard time getting the flame trap out of its housing. Finally, I used a screwdriver and applied a little force to get the whole housing out of the big intake hose. After cleaning both pieces thoroughly with carb cleaner, I put everything back the way it was before. Or so I thought…

A day later (on Tuesday) my wife complained about violent surging and rough idle after cold start. Since she did not complain on Monday, I assumed that this is a new symptom. When starting, the engine was surging to about 2000-2200 rpm and then dropping to about 1300-1500 rpm. Then it surged again to about 2000 rpm and then settled at about 1200-1400 rpm. Even after settling, it was kind of hunting around, but not as violent as in the first couple of seconds. Nevertheless, I checked all the connections around the intake hose again (without taking off the throttle pulley cover). It did resolve some of the surging problems temporarily, but the idle was still high. I also checked the wirings for IAC and TPS. While checking the flame trap connection, I accidentally cracked the flame trap housing and I dropped the o-ring and lost it! Oh yeah, and the “Check Engine” light finally came on. Bad luck?

On Wednesday, the rough idle and occasional surging was still present. I stopped by the dealer to get a new flame trap housing and the o-ring and started all over again. This time I did remove the plastic cover of the throttle linkage and … here it was! The throttle cable was stuck on the side of the pulley. I guess I accidentally dislocated it on Sunday. No wonder the car could not idle properly! I was relieved because I was already starting to prepare myself for the worst case scenario. Now, everything is back to normal. As the results, my car did get a brand new flame trap with o-ring and housing. Also, this little adventure helped me to bond closer with my Volvo. Finally, it made me order the Alex Peper’s obd-2 scan tool so that I can clear trouble codes myself. I will post an update about the tool when it arrives.

Lesson learned: be carefull with the throttle cable and throttle pulley next time you are working around TB!

Raphael