savannahvolvoguy Posted February 12, 2017 Report Share Posted February 12, 2017 Copy and paste from my cam seal thread to get started... Then some new developments. I recently did the TB on my XC70 and the whole procedure went smoothly right to the point when I started the car. It started right up but then proceeded to hunt for an idle. It would idle up and down for about 30 seconds or so before settling on its final normal idle RPMs. I assumed this might be not be too bad of a sign as maybe the computer was making some small adjustments or something. However... The first long drive I took with the car after the change I noticed that the fuel economy was somewhat reduced. It went from like 25 to 27 on the highway to something more like 23 or 24. Not a big change but I wouldn't really expect any change at all. I've also started to notice that maybe it doesn't have quite as much power and perhaps doesn't feel quite as smooth. It also doesn't sound like its making as much boost. It also seemed to me at the time that maybe it was a little more difficult to turn over with the new belt back on. At this point I'm not even sure if I'm just imagining this. It seems possible even that the gas mileage hasn't actually changed and I just hand't noticed that the gas mileage has reduced to its current level before doing the work. Its also possible that I haven't gone on a long drive with it in the winter months and perhaps the colder denser air might be making a difference in my gas mileage. The only thing I can think I could have done during a timing belt change is that maybe I got one of the cams off by a tooth. The confusing thing is that I would think that CVVT could either account for the one tooth variance or the car would throw a code of some sort. There are no warnings to speak of. At this point I've put about 500 miles on the car hoping it was a software thing or my butt dyno would figure out that nothing has changed but no such luck. So my question is... What could I have done? and am I just crazy? So in review. There are no OBD codes and the car has nearly stalled on startup once. Today I've checked the timing to make sure that all is well there and everything is perfect. I've seen in another thread someone talking about resetting the ECU by disconnecting the battery. Any chance that's all I would need to do? I always do TB changes with battery disconnected so the ECU should have "reset" when I did that. Is there anything else I could have done during the timing belt change that would have caused these issues? Again this was a rather smooth TB change. Probably my smoothest. The other weird thing I did perhaps was I started the car to check that the belt was riding evenly on the rollers with the accessory drive belt off. Could the car be holding a grudge from weird computer things that might have popped up when I did that? Could the near-stall yesterday have been unrelated? Perhaps a MAF starting to go? Thanks a lot for the input! Link to comment Share on other sites More sharing options...
Ihatespeedbumps Posted February 12, 2017 Report Share Posted February 12, 2017 If the timing is off the check engine light would be on after the second key cycle. It sounds to me like there is a small vacuum leak or the throttle body is dirty and this is coincidence. Link to comment Share on other sites More sharing options...
savannahvolvoguy Posted February 12, 2017 Author Report Share Posted February 12, 2017 I'm starting to suspect throttle body. When I start the car in the morning and it starts to idle high (you know... like normal) while the idle is settling down you can see the needle for the tach moving maybe 50 RPMs up and down until it settles down. The scanner shows there is a fluctuation in the idle of a couple RPM. Not enough to see or feel. If the ETM were to not behave as expected would that cause the car to stumble at startup? It also feels perhaps a little laggy now which may be related to delayed opening of the throttle. I even have a gasket in stock so maybe its time to pull it and see what happens. Link to comment Share on other sites More sharing options...
Ihatespeedbumps Posted February 12, 2017 Report Share Posted February 12, 2017 Just clean it out and see where you get. Be sure not to spray the cleaner directly into the throttle body, always needs to be sprayed on a rag first. If the deposits are especially stubborn use a brash wire brush or gently scrape with a screwdriver. Link to comment Share on other sites More sharing options...
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