Low/erratic idle when hot
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What the title says. Car starts and runs beautifully when cold. After reaching operating temperature, if I slow down (i.e. idle into a parking spot, reverse out of somewhere etc.) the idle dips, and it will occasionally die.
I found some vacuum diagrams and was going to try and take a look at the hoses. What else should I check?
Thanks!
I found some vacuum diagrams and was going to try and take a look at the hoses. What else should I check?
Thanks!
Last edited by benji808; 08-07-2023 at 11:27 PM.
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benji808 (08-08-2023)
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Ok, further testing: after driving about 15minutes, idling in a parking lot, the the engine speed bounces up down between 200 and 800. Otherwise seems to start, run,
and drive great.
vacuum hoses seem good (haven’t checked exhaustively but so far seem solid)
fuel pressure regulator holds vacuum
throttle body looks clean, and is gapped at .002”
Coolant temp sensor is showing proper resistances
it will start right back up so I doubt overheating electronics, but of course never say never
What else to check?
EDIT: After running the tests detailed here: O2 Sensor Test Information & Resetting the Light (jag-lovers.org) I believe the O2 sensor is bad. When I initially hooked up the multimeter, I registered voltage as expected. When I started the car and revved it for a while, the voltage was stuck high. I created a vacuum leak (used what I believe is the cruise control manifold port). The voltage did not respond immediately, then slowly, over a couple minutes, dropped to a low number. When I replugged the vacuum port, the voltage did not increase, but stayed "stuck" below 0.2. The engine ran rough for a bit then died. I'm interpreting that to mean that for whatever reason the O2 sensor is unresponsive or slow to respond to air/fuel mix changes, and should be replaced. Let me know if you have any different thoughts!
and drive great.
vacuum hoses seem good (haven’t checked exhaustively but so far seem solid)
fuel pressure regulator holds vacuum
throttle body looks clean, and is gapped at .002”
Coolant temp sensor is showing proper resistances
it will start right back up so I doubt overheating electronics, but of course never say never
What else to check?
EDIT: After running the tests detailed here: O2 Sensor Test Information & Resetting the Light (jag-lovers.org) I believe the O2 sensor is bad. When I initially hooked up the multimeter, I registered voltage as expected. When I started the car and revved it for a while, the voltage was stuck high. I created a vacuum leak (used what I believe is the cruise control manifold port). The voltage did not respond immediately, then slowly, over a couple minutes, dropped to a low number. When I replugged the vacuum port, the voltage did not increase, but stayed "stuck" below 0.2. The engine ran rough for a bit then died. I'm interpreting that to mean that for whatever reason the O2 sensor is unresponsive or slow to respond to air/fuel mix changes, and should be replaced. Let me know if you have any different thoughts!
Last edited by benji808; 08-08-2023 at 07:48 PM.
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