Why does my idle quality go to he!! with warmer temps?
11-26-2005, 10:17 AM
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Why does my idle quality go to he!! with warmer temps? Could someone explain why my idle in "D" is fine when the outside temps are below 40, but deteriorate steadily as temps increase? At 90 to 100 ambient temperatures, it feels like I'm sitting in a huge vibrator! There has got to be something funky going on... I have changed plugs and plug wires; no change. This car has done this almost from new... dealer is absolutely no help whatsoever (big shock), according to them it's "normal operation." I know that colder air is more dense, but I'm not educated enough to fill in the blanks. HELP!
11-27-2005, 10:03 AM
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Thanks. I have adjusted the throttle stop; 1 turn, unplug TPS, key on, key off, plug in TPS, etc. Seems to have helped cold weather idle but when it warms up outside it still idles like crap. Not sure why a "new" car with no mods (at the time) would require a custom tune to maintain consistent idle quality. The Predator was used initially to bump up idle speed 100 rpm; at 650 rpm the idle is perfectly smooth (except for the cam rock, which I fully expect and doesn't bother me). Drivability with a 650 rpm idle in "D" is compromised significantly. If this were a borderline race car, I wouldn't make a deal out of this. But this is supposed to be a premium high-performance GT; shouldn't idle like a 30 year old school bus when the weather gets warm.
Should I just shoot for a custom tune? Could this problem be fixed by a saavy tuner? Should I just invest in HPTuner and then spend the next year learning how to use it? I really like this car alot, otherwise I wouldn't be spending money to fix something that should be covered by the new-car warranty.
Should I just shoot for a custom tune? Could this problem be fixed by a saavy tuner? Should I just invest in HPTuner and then spend the next year learning how to use it? I really like this car alot, otherwise I wouldn't be spending money to fix something that should be covered by the new-car warranty.
11-27-2005, 12:15 PM
#5
Bone stock? A4s do idle pretty low because of the low stall torque converter. If raising the idle by 100 rpm didn't make it alot better, there is something mechanical wrong.
Don't mess with the tune; diagnois the real problem. I'd start by looking at your plugs and for vacuum leaks.
Don't mess with the tune; diagnois the real problem. I'd start by looking at your plugs and for vacuum leaks.
11-28-2005, 09:08 AM
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Raising 100 rpm did help smooth out the idle. It's just too irritating to drive that way all the time. I changed the plugs and plug wires... no difference. I have done an extensive vacuum leak check and found none. The car did have a vacuum leak on delivery, though. The HVAC control vacuum line was split; it was stuck in defrost mode under throttle. When you were at light throttle cruise, it would slowly go to vents that control was set on. This logically indicated to me that there was a vacuum leak; fuel rail cover had been snapped down onto one of the vacuum lines going to the heater control valve. I cut out the split section and re-connected; problem fixed. I even checked the power brake booster (some GTO's had been delivered with a defective brake booster vacuum check valve) but it checked out okay. The single biggest clue seems to be that it is temperature sensitive. Cold outside temperatures = smooth idle. Hot outside temperatures = crappy idle. I checked the IAC; it looked fine. I checked the TPS and it reads .61 volts at idle. I used my Predator to monitor IAT readings and it seems to be working; the idea there being maybe if the IAT wasn't functioning properly, the computer would always think the intake air was, say, 70 degrees, even when it was 105 and so wasn't compensating for warmer intake air, therefore leaning out significantly as ambient temperatures increased. Obviously, there are no codes being set; this is about the only thing the dealer service will do as far as diagnosing a problem... to them, no codes = no problem, regardless of how crappy the car idles.