Recently my 1999 S70 GLT engine IDLE RPM starts to oscillate/hunt between around 800 and 1300 and Check Engine light is on. A local technician said there is a faulty code with speed sensor and it costs $95 parts + 3 hours of labor. After spending $400, the RPM surge issue remains. Can someone suggest the possible cause of this problem ? Also, anyone knows a reputable Volvo shop around San Francisco Bay Area (I am in Hayward, CA but will drive for a good mechanic :-)
Please help. Thanks ! Ming
I assume GLT, that this is a turbo engine. The throttle plate might be gummed up with oil vapors. It is like the flue in a fire place. At Idle the plate is almost closed. The PVC systems sends oil vapors into the engine past the throttle plate.Hot oil vapors will collect on the cooler throttle plate. Over time the vapors will build up and restrict the air flow at idle. Idle will go below spec and the brain opens up the throttle unit to let more air past. Too much air, or higher idle the brain closes the t-plate. This is how or why the idle surge takes place. Cleaning off the oil junk residue from the throttle plate can restore smooth idle again. It can take 2 to 3 hours to remove the throttle plate to clean it. Sometimes cleaning the throttle plate can cause it to fail very soon. If the throttle unit is origional, it may be starting to fail. Sometimes updating the software can cause it to fail. All of the above is because it was about to fail any way. Something else you can try or have your repair shop try. This may or may not help. In the center of the intake manifold, below the fuel rail cover area is a black vacuum line. Cut off the steel band and carefully remove the vacuum hose from the brass nipple. If you cut the vacuum line, there is enough hose to cut the hose end off and put it back on latter. Get a 3 to 5 inch piece of rubber hose to go over the exposed nipple. Probably 5/16" or 3/8" hose will work. Push the short hose piece onto the brass nipple. Get a can of Carb cleaner. Put the plastic straw on the can place straw into the short hose. Put a rag around the straw and short hose. Spray carb cleaner into the intake for about 5 or 10 seconds. Do not let the straw blow off of the can into the intake. Let the cleaner set for 2 or 3 minutes. This hose area is almost top center of the throttle plate area. This will help to disolve the oil junk on the throttle plate. Install the removed vacuum line. You can use a regular plastic tie strap to secure the vacuum line onto the brass nipple. Do this cleaning outside in an open area. Hold the gas pedal to the floor and start the car. It will not even try to start at first. Too much carb cleaner being sucked into the engine. It might take 10 to 20 seconds of cranking for the car to try to start up. It will stumble really badly when it does try to start. Keep the pedal floored untill it does start and then maintain some rpm's above ldle for a few seconds or so untill it smooths out. It will blow a lot of white smoke out the tailpipe. This is the carb cleaner burning off. Try not the breath the vapors. If the ilde surge is due to a dirty throttle plate the above cleanig method should help.
BD
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"Ming" wrote in message news: snipped-for-privacy@z14g2000cwz.googlegroups.com...
I would check to make sure the air intake system is sealed up, such as all air cleaner snaps engages, no loose hose connections. I would look over every item carefully when the engine is running.
Also, try brickboard or swedespeed for similar posts.
That's the first sign of impending Electronic Throttle Module failure. Click this for lots of interesting reading.
I had the same problem with my 99 S70 T5. The Electronic Throttle Control System is the problem. Parts and labor ~ $900. This was done twice in 18 months.
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