I've got a 91 740 and when I'm at a stop light, the RPMs go up and down and up down, sometimes down to 500, sometimes up to 2000...

I just had the throttle body and the IAC cleaned, someone told me it could be my Regina system, f'ing up my fuel pressure.

Should I be worried? or will everything be OK?

Thanks,

jon

P.S. I need to give her gas everytime I start her up.

Does the "cycling" stop if you put the car in park, and take your foot off the brake? If so, then my bet would be on the brake booster check valve.

Jeff Pierce

The same thing happened to me with my 92 740 non turbo wagon. The Volvo dealer reset the idle control computer and the car has been running like a champ ever since.

Could be a faulty IAC valve. You could try unplugging the connector to the IAC valve and see if the idle stops going up and down. (The engine may also stall - which would not necessarly be an indication of failure.) If the idle does stop going up and down then I would suspect that it is the IAC valve. Even when they are clean and move well, the motor in the IAC can have a dead spot - and I think that this can cause the idle surge. I found one in mine a few years ago by testing with an ohm-meter and moving the valve - at one point the resistance went very high, indicating the dead spot in the motor. Also check the FAQ for a lots more info on the IAC valve.

Steve
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1986 745 w/ M46 200K since new, 1995 965 104K

I've had the same problem recently and just when I bought a can of carb cleaner (to clean the ICV) the problem went away.

One thing I did was put some CD2 into my fuel system. This does alot of work for the upper end of an engine.

Don't know per say that it helped but I am now okay.

I run my car hard which I believe Volvo's have always seemed to want.

Use Mobile 1, new oil filters regularly, and periodically run a tank full of premium through the car.

Good luck

rhodee

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1988 765TFM46 project car

"One thing I did was put some CD2 into my fuel system. This does alot of work for the upper end of an engine."

What is CD2? Sorry for the stupid question!

Thanks,

Jon

One or two hundred fluctuation would seem ok in a 15 year old car but 500 to 2000 shows some sort of problem maybe an intake leak somewhere. If you can't find anything obvious try the "propane test". With the engine running and the fan wind blocked go over the intake system with a small propane tourch to see if the gas causes any increase in idle. I suppose I should mention UNLITE propane tourch. Was the throttle body removed when it was cleaned? The throttle linkage could be too tight or the throttle positon switch missadjusted or maybe the switch plug is loose. Usually the throttle body gasket can be reused unless it was torn up alot but that could be a leak source.