1996 850 - Can a new fuel filter change idle speed????

2 weeks ago changed the fuel filter on my wife's 855. Bosch part, looked identical to the old Volvo one on the car. Total Mileage 80,000. Just drove it this weekend and noticed that idle in gear at rest is 1000 rpm, previously was about 850rpm. At rest in neutral (autobox) idle is 1300rpm, previously 900rpm. Car runs well, just did 200mile trip, all fine, gears change fine, engine smooth etc. Air filter, plugs, oil filter all replaced in last 3000miles (oem parts). Throttle body and flame trap cleaned 3000 miles ago (they were not very dirty at all). I checked for vacuum hose missing or broken and could not see anything adrift.I can't believe changing a fuel filter would affect the idle. Also, I can't see that I installed the filter incorrectly. It does not leak and the engine runs so surely its OK. Is it just a coincidence and maybe the Idle Control Unit is playing up? Any suggestions gratefully received

Chris

Reply to
Chris
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Another possibility is that the engine computer recalibrated to the better fuel flow of the new filter. This is a possibility if the fuel filter was very clogged and would fit with 80,000 mileage on the same filter.

Reply to
Walt Kienzle

While your suggestion is not beyond the realm of physical possibility, any car that had it's idle speed largely dependent on the rate of fuel flow from the tank would be really scary.

Reply to
Happy Trails

Update - at the weekend the high idle returned after we had been driving for about 5 km. I restarted the engine and it went back to

900rpm. I am now concerned that it is something electronic - would turnining the ignition off and restarting re-set something. Note that the Engine Check light is not illuminated. Something else I should add

- the ABS Control Unit is out of the car for repair, but I can't see this would have any impact.

Reply to
Chris

Chris, I believe your computer had come to misread things due to the corrosion you removed. By reinstalling it and simply restarting, the computer said, "Hey something is different. Let me check this out." After a short ride, it found where truth was and reset.

Interesting tip on a simple fix. Wanna bet the dealer had another, higher price solution? I also tend to think that an independent mechanic practiced in Volvos would have also come to your solution. He doesn't have quite the same reinforcement contingencies a dealer has.

Chuck Fiedler Nothing but Volvo since 1974 Oh, yeah, I finally got rid of my 1960 Austin Healey

Reply to
Chuck Fiedler

Further update. It is still idling irregularly. Sometimes 900rpm, then it goes to 1400rpm. My initial view that it was the idle control valve connections now appears prematurely optimistic. It has been suggested to me that the front o2 sensor could be playing up. The car has

81,000miles on original o2 sensors. Could this cause a high idle? What makes me a bit dubious though is the the check engine light is not illuminated. I would have thought that a bad o2 sensor would have been detected by the EMS and reported? Given the mileage, I am tempted to replace the front o2 sensor as a matter of course as I understand they have a max life or around 100,000miles anyway, and it seems like a 30 minute job. Any thoughts?
Reply to
Chris

I would give that a try. Actually, *I* would take it to my mechanic who has all the diagnostic stuff and have him fix it but since you're shooting in the dark, give that a try. It certainly can't hurt and self-repair is cheaper than paying for it. Self-diagnosis OTOH, can be rather expensive in the long run.

Reply to
Chuck Fiedler

While the O2 sensor may be weak (Bosch recommends 60,000 mile replacement intervals. But keep in mind they are the primary manufacturer of this costly product), I don't think it is the source of your problem. I agree that a substantial O2 sensor problem would trigger the check engine light if that was the primary cause. Also, the O2 sensor affects fuel mixture (and fuel economy) more than having to do with erratic idle speed. From your latest update/description, it is more likely that you have a cracked/intermittently disconnected vacuum line somewhere that is playing havoc with your idle speed. This is something you can check yourself because parts are very cheap (snip the end off a hose and reconnect to verify the problem), but very labor intensive. Professionals charge dearly for their time and don't always do a thorough job when it is this boring. Don't confuse/misconnect the hoses. That is when the professionals charge the really high labor rate to correct an amateur's mistake.

Reply to
Walt Kienzle

Walt Kienzle?! Is this the Walt Kienzle who used ot be in Minneapolis who I would take my 544 to for miraculous cures?

If so, where are you now?

Please email me with particulars.

Chuck Fiedler Nothing but Volvo since 1974

Reply to
Chuck Fiedler

Sorry, not the same Walt Kienzle (there are two of me??).

Reply to
Walt Kienzle

I don't know if there are two of you but I knew a Walt Kienzle thirty years ago and my father did his bookwork. He was a wizard at fixing Volvos. I heard he had moved to the Dallas area long after i had.

I sorta figgered there are a limited number of folks named Walt Kienzle and if you filter it through Volvo, you'd get a pretty small set of hits.

Sorry if I hit the wrong guy but glad to make your acquaintance.

Chuck Fiedler Nothing but Volvo since 1974

Reply to
Chuck Fiedler

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