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

This evening I removed the idle control unit. The valve inside was moving quite smoothly but I cleaned it up anyway. The electrical connectors had a small amount of turquoise corrosion. I cleaned these up also and put it all back together. Only took 20 mins. When I started the engine it immeditely settled into a smooth idle at 900rpm in Park. Not possible to do a test drive so will wait until tomorrow. Could the slight corrosion on the connector hav caused my problem, I wonder.

Car is now idling smoothly at 900rpm in neutral. So it must have been either the corrosion on the electrical connectors or sticking valve in idle control unit

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.

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.

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

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

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

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

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.

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.

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

it is more likely that you have a

I did a quick check of all the vacuum hoses when the problem first mainfested - could not see enything wrong, but I shall do a more thorough check as you suggest. Even though it is 12 yrs old all the hoses were surprisingly supple. They did not seem to have hardened/ cracked with age and heat. Thanks

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

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