74Adam Posted March 18, 2011 Share Posted March 18, 2011 Well, maybe not "off topic" since this is the general board, but anyway..... So, in the span of several months my otherwise miserly toyota has gone from upper 30's on the highway to upper 20's. It is completely stock (it's a corolla for eff's sake). The tire pressure is good and they are the factory size, the oil is fresh Mobil 1 5w-20 synthetic per specs, I have replaced the plugs with NGK iridium's per specs, the air filter is clean. The car has 75,000 on it and otherwise appears to be running perfectly fine. It feels like it has the same amount of power as it always has (which isn't much). It's a stick. Just got back from my sister's and my brother in law has a diagnostic tool that hooks up to a laptop. No codes came up but it read that the engine had a 12% load at idle which he thought was odd since his Subaru shows zero load at idle. It may just be a difference in the ECU's (I really don't know). It also read that the throttle position was 16.5% at idle. That DOES seem strange as I assumed that all newish cars control idle with an IAC not at the throttle plate. Well, this is getting long but I would appreciate any thoughts as I can't arbitrarily throw money at my car at the moment. thanks in advance Quote Link to comment Share on other sites More sharing options...
75280z Posted March 18, 2011 Share Posted March 18, 2011 O2 sensor is sometimes to blame for failing gas mileage. I don't know about the 12% idle thing, the throttle position does seem a little weird. Quote Link to comment Share on other sites More sharing options...
jasper Posted March 19, 2011 Share Posted March 19, 2011 No more iac (idle air contol valve). Drive by wire. Throttle position determines idle speed. (great for traction control) I don't even pay attention to customers with MPG concerns. (Toyota) RARELY does anyone DOCUMENT their mpg. The ECM's are very sophisticated, and would know if something was amiss. What has the weather and temperatures been like for the past several months? Have the fuels been reformulated for temperature changes? Has E85, or oxygenated fuels been in use?? Are you the only driver? More traffic than usual, Driving faster?? Do you now warm your car up on cold mornings,maybe to deice?? All these things ,and more, kill mpg. Quote Link to comment Share on other sites More sharing options...
74Adam Posted March 19, 2011 Author Share Posted March 19, 2011 Thanks guys. It's not bad enough that I am going to take it in at the moment but I'll just have to keep an eye on it. Jasper, thanks for educating me. I didn't realize that IAC's were "obsolete". I really can't think of anything that has been even slightly different regarding my driving conditions or habits. I live in Dallas and except for a few weeks ago we haven't had ice on the windshields. This is something that has been going on for several months now. I don't "document" my mileage to the extent that I keep a log book, but I am one of those anal people that is very aware of such things. Thanks again guys. Quote Link to comment Share on other sites More sharing options...
auxilary Posted March 20, 2011 Share Posted March 20, 2011 this might sound stupid, but have you hit a bad streak of red lights? my mazda 3 can eek out 31mpg on highway, but once i get into the city, fuel economy dies. this weekend i drove around parking lots more than usual, and city driving brought my average from 29mpg to 26. other than that, try resetting your ECU. disconnect battery for 5 minutes or so, or unplug the ecu for the same amount of time. it might take 200-400 miles for the ecu to recalibrate itself, so you may get worse than advertised fuel economy for that time as it uses default mapping Quote Link to comment Share on other sites More sharing options...
randy 77zt Posted March 21, 2011 Share Posted March 21, 2011 Maybe the thermostat in the cooling system is stuck open?Some cars wont log a trouble code for this .Car will remain in open loop status or run a little richer.Tstat can be checked in a pot of water with a thermometer.But you wife might not like car parts on the stove Quote Link to comment Share on other sites More sharing options...
74Adam Posted March 22, 2011 Author Share Posted March 22, 2011 That's an interesting thought Randy (and no wife to worry about!). May just try that and resetting the ECU may be worth a shot as well. 75,000 miles too soon to do an fuel system/injector cleaning? I tend to think so but what say ye? Quote Link to comment Share on other sites More sharing options...
dan5138 Posted March 22, 2011 Share Posted March 22, 2011 Don't put any fuel injector cleaner in it, modern injectors are supposed to be self cleaning, and at 75k they're relatively new. The first thing that needs to be done is hook up a real scan tool to it and see where long term fuel trim is at while cruising on the highway. This will usually point you in the right direction as far as it being a mechanical/electrical issue. O2 sensors can become lazy ( doesn't switch very quickly) or biased( the always read rich or lean). Best way to test an O2 is check it's pattern with a lab scope. As far as load at idle anywhere between 0% - 20% is normal this varies by manufacturer, lopp status, and idle speed. Quote Link to comment Share on other sites More sharing options...
74Adam Posted March 22, 2011 Author Share Posted March 22, 2011 Ok Dan. Sounds reasonable. Thanks. Quote Link to comment Share on other sites More sharing options...
auxilary Posted March 23, 2011 Share Posted March 23, 2011 That's an interesting thought Randy (and no wife to worry about!). May just try that and resetting the ECU may be worth a shot as well. 75,000 miles too soon to do an fuel system/injector cleaning? I tend to think so but what say ye? Well, the best thing about resetting your ECU is that it's free Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.