Low idle problems
$400chevymetro
06-02-2007, 11:25 AM
My 98 1.0 5 sp. started acting up a few days ago hopefully someone has had a similar problem and figured it out. When coming to stop if I kick it out of gear it while coasting it idles normally but when I come to a stop it will idle down till it almost dies then it will idle back up, it repeats this cycle as long as I'm sitting. Thanks in advance for any help.
1994 firefly
06-09-2007, 05:05 PM
Maybe check your PCV valve. I had a similar problem (not on a metro mind you) where it would do the same thing. try disconecting the pcv valve and blowing through it. It's a one way check valve that will let gasses out of the crank case to be burned. Shake the valve, if it rattles its' probably fine, if not, try blowing through it from the side that goes to the crank case, if you can't pass air through it, she's dead.
$400chevymetro
06-09-2007, 05:24 PM
Thanks for the reply but the PCV valve is fairly new and in working order. I just replaced plug wires and distributor cap. They didn't have the rotor in stock but it looks pretty good and I'll get one next time I get to town. I've been thinking it might be the O2 sensor. Damn things are pretty expensive I wonder if there is anyway to check them? Tried plug wires and cap but no help for $30, they really needed to be replaced so that isn't to bad. But the O2 sensor is a bit pricey if that's not the problem. My other thought was maybe the injector is clogged or worn out, the car does have 182,000 on it. Need to get over to father in laws and borrow his timing light so I can see what kind of cone the injector is putting out.
91Caprice9c1
06-10-2007, 03:39 AM
My 98 1.0 5 sp. started acting up a few days ago hopefully someone has had a similar problem and figured it out. When coming to stop if I kick it out of gear it while coasting it idles normally but when I come to a stop it will idle down till it almost dies then it will idle back up, it repeats this cycle as long as I'm sitting. Thanks in advance for any help.
Take off the air filter housing and make sure the Throttle body is clean, carbon build up in the throttle body is not only common to many cars (and especially common to ours), it plays havoc on idle quality.
Make sure you have no vacuum leaks. A vacuum leak will cause an unstable idle.
Verify that you EGR is not operating when it shouldn't be. Namely, at idle.
Unplug your Coolant temp sensor(s) while idling (one at a time if you have two) at the coolant outlet, and possibly one in the throttle body facing the driver side of the engine compartment. If either of those changes the idle condition you probably have one gone fubar, or a clogged coolant passage. This has happened to me, but it effected performace as well as idle quality.
Back probe the TPS with a DIGITAL Multi-meter and verify that it is properly adjusted via a service manual. I have found on my pre-96 cars that 0.5-0.6volts works well at idle although the manual suggests 0.9volts I think, and the TPS is a little tempermental so be packed with patience. I don't remember which two of the three wires to probe, but go through the possible combinations until you find one that varies voltage with throttle position and you found the two you need to check at idle. Maladjusted TPS's will create an unstable idle.
Unplug the MAP sensor while idling, your car should stumble, almost die, and then recover. If the problem goes away, make sure the tube from the sensor to the engine is clear and flows air, and then backprobe the sensor and compare to spec. via service manual.
Check the vaccuum for a healthy, solid reading. I have a metro that started idling like that because of terribly weak valve springs. This will represent itself on the vacuum gauge in the way of a needle that will not stay still (but move rapidly) at any rpm. Weak valve springs will effect performance in the higher rpms as well as idle quality.
You can check the O2 sensor with a scan tool (or preferably an oscilloscope) but a scan tool is easier to come by. Autozone (or similar parts stores) will let you use their's for free. You're looking for a voltage output that varies from ~0.3-0.8 volts in a regular pattern once the engine has reached operating temperature (fans kick on and off). This will almost certainly not be your problem. Not only because a bad O2 sensor is unlikely to tamper with idle speeds, but more importantly because if the sensor had a problem, your check engine light would be on. BTW - if you decide to check anyway, you want to check sensor 1, 1 (or, bank 1, sensor 1).
As long as you have a DMM you can do these for free (except for fuel costs) and narrow it down quite a bit. Thats all for now, report back, and I'll think more.
MechanicMatt
Take off the air filter housing and make sure the Throttle body is clean, carbon build up in the throttle body is not only common to many cars (and especially common to ours), it plays havoc on idle quality.
Make sure you have no vacuum leaks. A vacuum leak will cause an unstable idle.
Verify that you EGR is not operating when it shouldn't be. Namely, at idle.
Unplug your Coolant temp sensor(s) while idling (one at a time if you have two) at the coolant outlet, and possibly one in the throttle body facing the driver side of the engine compartment. If either of those changes the idle condition you probably have one gone fubar, or a clogged coolant passage. This has happened to me, but it effected performace as well as idle quality.
Back probe the TPS with a DIGITAL Multi-meter and verify that it is properly adjusted via a service manual. I have found on my pre-96 cars that 0.5-0.6volts works well at idle although the manual suggests 0.9volts I think, and the TPS is a little tempermental so be packed with patience. I don't remember which two of the three wires to probe, but go through the possible combinations until you find one that varies voltage with throttle position and you found the two you need to check at idle. Maladjusted TPS's will create an unstable idle.
Unplug the MAP sensor while idling, your car should stumble, almost die, and then recover. If the problem goes away, make sure the tube from the sensor to the engine is clear and flows air, and then backprobe the sensor and compare to spec. via service manual.
Check the vaccuum for a healthy, solid reading. I have a metro that started idling like that because of terribly weak valve springs. This will represent itself on the vacuum gauge in the way of a needle that will not stay still (but move rapidly) at any rpm. Weak valve springs will effect performance in the higher rpms as well as idle quality.
You can check the O2 sensor with a scan tool (or preferably an oscilloscope) but a scan tool is easier to come by. Autozone (or similar parts stores) will let you use their's for free. You're looking for a voltage output that varies from ~0.3-0.8 volts in a regular pattern once the engine has reached operating temperature (fans kick on and off). This will almost certainly not be your problem. Not only because a bad O2 sensor is unlikely to tamper with idle speeds, but more importantly because if the sensor had a problem, your check engine light would be on. BTW - if you decide to check anyway, you want to check sensor 1, 1 (or, bank 1, sensor 1).
As long as you have a DMM you can do these for free (except for fuel costs) and narrow it down quite a bit. Thats all for now, report back, and I'll think more.
MechanicMatt
$400chevymetro
06-10-2007, 03:33 PM
Matt thanks for the suggestions. I forgot to mention MPG has gone from 50 to 44 and performance has dropped just a little, that's one reason I thought it might be an O2 sensor. Thanks again and I will certainly start checking out some of your suggestions.
sas95
06-24-2007, 11:47 PM
And, do you have any diagnostic trouble codes (DTCs)? Check-engine light on?
Also suggest checking your Idle Speed Control system as much as you can to see it's working correctly.
Also suggest checking your Idle Speed Control system as much as you can to see it's working correctly.
Automotive Network, Inc., Copyright ©2026