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98 S70 Wandering Idle after PCV Job. Corrected itself? Topic is solved

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december454
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december454

98 S70 Wandering Idle after PCV Job. Corrected itself?

Post by december454 » Sun Jun 30, 2019 3:03 pm

TLDR: Do PCV job, car gets surging idle once warm; next day it is magically fixed.

Hello MVS, first time poster looking for advice. I have lurked here before for advice, and I know you all can be a great help.

This weekend I finally had a good chance to replace the PCV system on my 1998 S70; it is an N/A model with about 120,000 miles. The system wasn't too clogged, but it did fail the glove test, and there was some smoke coming out of the dipstick tube. I purchased KIT-523201 from FCP Euro for the parts.

The install itself went well enough. I looked over a few guides prior to the job and followed along with the video from FCP Euro while working. With everything removed, I did take off the fuel-rail to replace the o-rings, and I also removed and cleaned the throttle body.

After finishing everything up in the evening; all seemed well with the car at first. It started up fine, passed the glove test, and idled normally. I then took it out for a test drive and noticed some problems after about five minutes had passed and the engine was up to temp. Whenever I let off the throttle and coasted, the engine would surge between maybe 1000-2000 RMP (I don't quite remember). Whenever you gave it throttle, it seemed to run fine. Then as I was pulling back into my driveway (in reverse with no throttle input) the engine nearly died; it would wander from below 500 RPM to over 1000. It did that for maybe 20 seconds before I shut it off in front of my garage; it felt like it would have stalled it I didn't give it throttle. About 15 minutes later after some research, I went and quickly pulled the car into my garage; now it seemed to be back to normal and running fine.

The next day I started trying to track down my problem. I checked all of my electrical connections (MAF sensor, throttle position sensor, idle air control valve, etc), and all of my vacuum connections. There was no gas seeping from the injectors; the intake manifold and throttle body gaskets seem to have mated properly. I also checked the throttle position sensor with a code reader; idle reads as about 10.6% throttle and floored it reports around 86%. Maybe a bit off, but it is definitively sending data. Everything seemed good.

I then decided to start the car and spray around with a can of throttle body cleaner. The car did not start the first time. (I have had this happen once every couple months; I think it may be the fuel pump relay, not sure. I don't know if this was related to my idling issue.) The second time though it started right up and idled perfectly. For about ten minutes, I let it idle and get up to temperature. While it was idling, I began spraying throttle body cleaner all around the manifold gasket, injector seals, throttle body, vacuum lines, and anywhere else I could think of. Nothing happened; the engine never surged while I was spraying.

After this, I decided to go for another drive while monitoring revs with my code scanner. During the first few minutes I think the car may have stumbled once while coasting to a stop, but it may have been my nerves getting to me. I drove around for about an hour and couldn't get the issue to reappear. I did tons of coasting and stop and go through some residential areas, and didn't notice a thing. It acted fine on the highway as well, and it didn't miss a beat at wide open throttle either. My scanner says the engine never dropped below 780 RPM, and I think that was when I was backing out of a muddy driveway.

So I am confused, and I am curious to see what you all have to say. I have read over most every forum post I managed to find on the subject, and don't know what to think. On one hand I am glad that my car seems to be running properly, but on the other I am concerned that this issue may not truly be solved. Sorry for the wordy post; I just wanted to fill in as many gaps as possible.

Thank you all.



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GlennG2759
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GlennG2759

Re: 98 S70 Wandering Idle after PCV Job. Corrected itself?  Topic is solved

Post by GlennG2759 » Sun Jun 30, 2019 4:23 pm

Did you disconnect battery? Could possibly be a ECU relearn?



december454
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december454

Re: 98 S70 Wandering Idle after PCV Job. Corrected itself?

Post by december454 » Sun Jun 30, 2019 4:28 pm

Yes, I did disconnect the battery.

Could the ECU still have needed to adjust anything even if the battery was disconnected?

Thanks for the reply.



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Re: 98 S70 Wandering Idle after PCV Job. Corrected itself?

Post by GlennG2759 » Sun Jun 30, 2019 4:35 pm

Especially if the battery was disconnected. I think if you search this site you'll find there is actually a process to it.
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december454



december454
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december454

Re: 98 S70 Wandering Idle after PCV Job. Corrected itself?

Post by december454 » Sun Jun 30, 2019 5:08 pm

Wow, yeah I just looked around a bit at ECU relearn. I didn't know resetting the ECU could have such pronounced effects. And come to think of it, it almost felt like the transmission was shifting somewhat smoother after this as well.

I'll read up some more on the whole process; hopefully that's all it was.

I'll leave this thread open for now in case anyone has something else to add. I will see if anything surface in the next few days of driving.

Thank you very much for the response.



december454
Posts: 4
Joined: Sun Jun 30, 2019 12:50 pm
Year and Model: 1998 S70
Location: Texas
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december454

Re: 98 S70 Wandering Idle after PCV Job. Corrected itself?

Post by december454 » Sat Jul 06, 2019 2:26 pm

It has been a week and I have put a few hundred miles on the car; I think everything is good. No problems have reappeared.
It seems that it was just ECU relearn. Thanks for the insight.

Marking this thread as closed.



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