Rough Idle - Oxygen Sensor?
03-20-2007, 12:02 AM
#1
Burning Brakes
Thread Starter
Rough Idle - Oxygen Sensor?
My 86.5 fires up no problem and idles fairly smoothly at first, right around 775-800 RPM. It actually is smoother at about 1100. But that's not what I am tackling right now.
When I start it and let it idle, it is okay for about 15 seconds. If I then rev it and let it idle again, the idle becomes rougher and the fuel mixture is stinky rich.
Is that the O2 sensor? As far as I know it is the original sensor and 74K miles.
Thanks,
Matt
When I start it and let it idle, it is okay for about 15 seconds. If I then rev it and let it idle again, the idle becomes rougher and the fuel mixture is stinky rich.
Is that the O2 sensor? As far as I know it is the original sensor and 74K miles.
Thanks,
Matt
03-20-2007, 12:15 AM
#2
Burning Brakes
I would guess that it is not the O2 sensor because it would act up at differnet conditions, not just idle. When it first starts it should be running a little rich to deal with the cold intake, etc. but it sounds like the cold start enrichment doesn't turn off. I would guess temperature sensor or conections to it/them. I would check the Temp II sensor first.
03-20-2007, 12:16 AM
#3
Burning Brakes
I would guess that it is not the O2 sensor because it would act up at different conditions, not just idle. When it first starts it should be running a little rich to deal with the cold intake, etc. but it sounds like the cold start enrichment doesn't turn off. I would guess temperature sensor or conections to it/them. I would check the Temp II sensor first.
03-20-2007, 12:42 AM
#4
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Hello members i had the same problem and replaced everything except oxygen o2 sensor.I asked Tom at 928 and ruled it out from beginning,but i decided to changed last weekend and it solved the problem.Parts and labor 150.00-whew i thought i was the injection computer... 
03-20-2007, 12:48 AM
#5
Rennlist Member
Originally Posted by RED SHARK 1990
Hello members i had the same problem and replaced everything except oxygen o2 sensor.I asked Tom at 928 and ruled it out from beginning,but i decided to changed last weekend and it solved the problem.Parts and labor 150.00-whew i thought i was the injection computer...
I have exactly the same symptoms ,replaced almost everything suggested and more.....perhaps the oxygen sensor is next.
03-20-2007, 10:40 AM
#7
Rennlist Member
count me in - my 86.5 started having this rough idle problem too....can somebody list all of the things that are fairly inexpensive and somewhat easy for us DIY guys to do at home? (like the Temp II sensor, the O2 sensor, etc). I got my car last fall, it was a FL car, had lots of work done, but some of these things under the hood are baked, and I suspect this is the problem. Also, I'd rather not tear into a MAF project if I don't have to...
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03-20-2007, 10:54 AM
#8
Burning Brakes
Thread Starter
Originally Posted by linderpat
count me in - my 86.5 started having this rough idle problem too....can somebody list all of the things that are fairly inexpensive and somewhat easy for us DIY guys to do at home? (like the Temp II sensor, the O2 sensor, etc). I got my car last fall, it was a FL car, had lots of work done, but some of these things under the hood are baked, and I suspect this is the problem. Also, I'd rather not tear into a MAF project if I don't have to...
I had my MAF rebuilt. It's probably easier to do than an O2 sensor. It's easy to get to, but you're out of commission while you have it rebuilt.
I am going to test my temp sensors and O2, and likely replace O2 if it's not corroded to the pipe since it's pretty old. I'll report back on whether it makes a difference.
Matt
03-20-2007, 11:09 AM
#9
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Matt,
I had some rough idle problems that I solved before I replaced my O2 sensor (if it's original I'd replace it anyway). The cause of mine was dried out/loose rubber fittings on the airboxes and intake. The replacement set for this is not expensive. I know you just got your MAF back, is it seated properly? Possibly you've got a vacuum leak?
Just my .02
BTW- My 02 sensor was part of the cat pipe so I just had to replace it. Might as well go with SS crossovers with high flow cats while your in there
.
I had some rough idle problems that I solved before I replaced my O2 sensor (if it's original I'd replace it anyway). The cause of mine was dried out/loose rubber fittings on the airboxes and intake. The replacement set for this is not expensive. I know you just got your MAF back, is it seated properly? Possibly you've got a vacuum leak?
Just my .02
BTW- My 02 sensor was part of the cat pipe so I just had to replace it. Might as well go with SS crossovers with high flow cats while your in there
.
03-20-2007, 11:34 AM
#10
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I had that same problem last year. I, too changed everything. But the final culprit turned out to be bad wiring from the throttle position switch to the LH computer. The early part of the TPS movement handles the idle business at the LH. There are many posts about trouble-shooting the TPS circuit. Once I got that solved, the engine started up right on the money and settled in at 640 rpms. Also, along the way I found a bad pressure regulator (passenger side, just in front of firewall near end of fuel rail). Gas was seeping past it into the vacuum hose. It's easy to check. Getting to the TPS means removing the intake, though.
03-20-2007, 02:32 PM
#12
Burning Brakes
Thread Starter
Originally Posted by NJSharkFan
I had some rough idle problems that I solved before I replaced my O2 sensor (if it's original I'd replace it anyway). The cause of mine was dried out/loose rubber fittings on the airboxes and intake. The replacement set for this is not expensive. I know you just got your MAF back, is it seated properly? Possibly you've got a vacuum leak?
Other things that I need to do still are run a tank with Techron. I haven't done that and check my vacuum lines. Cursory glance they look alright, but I haven't really dug into them and I have a new set ready.
Matt
03-20-2007, 02:38 PM
#13
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Matt,
I'm sure you know this, but don't meter across the two leads of the temp 2 sensor, there are two different sensors in there, and to test them you meter them from each lead to ground (BTDT).
I'm sure you know this, but don't meter across the two leads of the temp 2 sensor, there are two different sensors in there, and to test them you meter them from each lead to ground (BTDT).
03-20-2007, 02:47 PM
#15
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A new O2 sensor wouldn't hurt, especially if the one in the cars has some miles.
It took a while for me to get the purrfect idle. I had problems with vacuum leaks, non-resistor plugs w/non-Bosch ignition amps, among others. The last two problems were:
Also, restoring the front damper reduced the raw gas smell on startup with the )(-pipe.
It took a while for me to get the purrfect idle. I had problems with vacuum leaks, non-resistor plugs w/non-Bosch ignition amps, among others. The last two problems were:
Originally Posted by PorKen
{Check} the ignition advance at idle{.} It should be 10-13°. When setting the idle, with the test plug connected C-B, the idle should be 680±40, and the advance is only ~6°.
If the idle throttle switch is disconnected/broken, the advance will be >20° at idle, which makes the rpms drop out occasionally, and the idle stabilization becomes very heavy handed.
The front fuel pressure damper has an effect on the idle. I found by accident that mine was not working because I had pushed the main large vacuum line too far into the rubber 'manifold', so it blocked the outlet to the front damper. If you put your hand on the damper, you should feel some pulsations if it is working. I think restoring the damper also helped with infrequent hard warm starts too, but it has only been a few days since I fixed it.
If the idle throttle switch is disconnected/broken, the advance will be >20° at idle, which makes the rpms drop out occasionally, and the idle stabilization becomes very heavy handed.
The front fuel pressure damper has an effect on the idle. I found by accident that mine was not working because I had pushed the main large vacuum line too far into the rubber 'manifold', so it blocked the outlet to the front damper. If you put your hand on the damper, you should feel some pulsations if it is working. I think restoring the damper also helped with infrequent hard warm starts too, but it has only been a few days since I fixed it.