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Car: 2003 9-5 Linear, AT with Aero stage 1, 138K miles
When in bumper-to-bumper traffic, noticed that the engine speed stayed at around 1,200 to 1,500 rpm, car wanting to keep moving with my foot off the pedal (w/o braking.) Once the car comes to stop, it idles at the normal rpm and stays there. In Neutral or Park, when revving it up and sometimes the engine stays around 1,500 rpm for long time (i.e. over 1 minute.)
OBD II codes seen: P0507 (idle too high), P0455 (leak in EVAP purge line) and P0171 (lean mixture).
Initially suspected vacuum leak, replaced all hoses with 4mm silicone went them over many times for a few days. Checked each connection with MityVac and no leaks. All check valves open and close fine. Canister purge valve not stuck and working fine (checked with PWM signal), normally closed holding vacuum. I ruled out the vacuum leak as a root cause.
Then checked the TB (still original.) Cleaned inside (last done probably about 40K miles ago), some black residue at the butterfly but no hard build-up. No error codes so thought it is OK... drives fine, holds highway speed with cruise control just fine. Also cable is not too tight.
More driving and trying to figure out the trigger... and just noticed that whenever the engine speed gets stuck at higher rpm than normal idle speed (gear in N or P), AC compressor is on. So I turned ACC off just to try it and the engine speed dropped down to normal idle speed!!! I revved it up over 2,000 rpm several times trying to get it stuck at higher speed, but it always dropped nicely to normal idle speed. Then I flipped the AC back on and revved it up, and sure enough I could get it stuck at the higher rpm (not every time but 70-80% of tries), then idles back to normal with AC turned off (this happens 100% of time). So I basically could turn 'the high idle' on and off with AC!!!
My AC is all original, never recharged, and still blows cold air (colder than my 2009 Audi A3). It appears as if the throttle body is trying to compensate AC compressor load too much, causing higher idle speed. Is this a sign of a tired throttle body (i.e. solenoids), even though no fault codes yet? Or is there anything else that I should check into?
I could just get a rebuilt TB (probably not much life left anyway...), but I would like more confidence with my diagnosis before pulling a trigger. I appreciate your comments/ advise on this issue.
Thanks!
posted by 172.5.11...
, Sun, 25 May 2014 12:55:24, Sun, 25 May 2014 17:42:12, Mon, 26 May 2014 11:36:21
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