Hunting idle only while warm.
Posted: Sat Dec 08, 2007 12:48 am
This is sort of a recurring but seemingly intermittent problem that started about around the time I pulled the engine out last.
On any time I crank the car when it's cold, it starts and will idle fine on idle enrichment, but about the time it comes off of idle enrichment (cold start warmup) the idle will start hunting.
it's not bad, the normal idle for the last two years has been around 650-750rpms, but now it will idle there for a moment, maybe longer, then bounce down to 450-500rpms; the stall point is somewhere around 400rpms.
I've had it stall on me twice now, once I was sitting at the race track, car was warming up, gave it a little throttle up to about 1500rpms for a minute or two, let my foot off the throttle and the engine stalled, it wasn't violent; infact I didn't notice till I looked down at the gauges.
Second time was on the interstate, clutched in from running it at about 3000rpms in 5th gear (somewhere around 80mph) as I approached slow traffic, had my foot on the brake, traffic cleared up a little bit, looked down and had blinky lights flashing at me; first thought was "oh shit: I've popped a belt off, thrown a rod AND my brakes are shot" but I realized the tach registered 0 so I cranked it back up no worries.
It's not much of a concern now because it's not causing me driveability problems, but I suspect it's a symptom of something brewing and wanted to know if anyone else had any ideas.
No particular trama to the O2 sensor or the MAF sensor, both still read fine according to vrg's scan tool which I use periodically.
engine seems to lean out a little when it does this (O2 sensor goes lean) and I don't smell rich fuel, but by this warmup stage I shouldn't. I can't really tell if it's an actual lean condition because it only bounces to 0 volts then comes right back up, it doesn't hang out (as if it were a fueling issue)
the time between the idle hunt cycle can be as short as 20 seconds or as long as 2 minutes.
any thoughts?
On any time I crank the car when it's cold, it starts and will idle fine on idle enrichment, but about the time it comes off of idle enrichment (cold start warmup) the idle will start hunting.
it's not bad, the normal idle for the last two years has been around 650-750rpms, but now it will idle there for a moment, maybe longer, then bounce down to 450-500rpms; the stall point is somewhere around 400rpms.
I've had it stall on me twice now, once I was sitting at the race track, car was warming up, gave it a little throttle up to about 1500rpms for a minute or two, let my foot off the throttle and the engine stalled, it wasn't violent; infact I didn't notice till I looked down at the gauges.
Second time was on the interstate, clutched in from running it at about 3000rpms in 5th gear (somewhere around 80mph) as I approached slow traffic, had my foot on the brake, traffic cleared up a little bit, looked down and had blinky lights flashing at me; first thought was "oh shit: I've popped a belt off, thrown a rod AND my brakes are shot" but I realized the tach registered 0 so I cranked it back up no worries.
It's not much of a concern now because it's not causing me driveability problems, but I suspect it's a symptom of something brewing and wanted to know if anyone else had any ideas.
No particular trama to the O2 sensor or the MAF sensor, both still read fine according to vrg's scan tool which I use periodically.
engine seems to lean out a little when it does this (O2 sensor goes lean) and I don't smell rich fuel, but by this warmup stage I shouldn't. I can't really tell if it's an actual lean condition because it only bounces to 0 volts then comes right back up, it doesn't hang out (as if it were a fueling issue)
the time between the idle hunt cycle can be as short as 20 seconds or as long as 2 minutes.
any thoughts?