1994 Volvo 850 Idling problems

hendricksl · Post by **hendricksl** » 17 Feb 2009, 13:10

I have a UK 1994 M Reg Volvo 850 with the 2.5 5 cylinder motor 188, 000 miles. It idles erratically between 500 and 1000 RPM, it doesnt die but just constantly fluctuates between them RPM's. It only does it every once in while when it rains alot or hit a deep mud puddle, after that it idles that way for two days and then clears up like nothing happened. Most of the time it runs and idles great. It is a great running car, we take it everywhere. I was frustrated with it yesterday and cleaned up the throttle body and all the hoses to see if there were any leaks and put it all back together last night and still had the problem. Started it up this morning and no problems all day, but I know once we get another rain it will start up again. Any help would greatly be appreciated

meteg · Post by **meteg** » 17 Feb 2009, 14:46

hello,

first check the distributor cap,rotor and plugs and the plug cables.then check the IAC valve(idle air control valve) make sure the items mentioned above are good.you say the throttle body is cleaned so that is excluded...

good luck

Craigd2599 · Post by **Craigd2599** » 17 Feb 2009, 15:01

sounds like the MAF. Maybe a bad seal on the connector.

Post by **kelvin6** » 17 Feb 2009, 21:00

Actually i'm still experiencing this problem myself, rain or no rain. It seems to be triggered by vibration or hitting broken/rough roads and or pot holes.

I cleaned out my MAF, and checked its specs with a multimeter and it seems to be in check.

So far, i've taken out the TCU and the ECU from the car (for a few hours) to reset both computers, and it seems to be working. The idle is maintained better...

My next course of action, if it returns or not, is to go ahead and clean the IAC valve as i'm sure with over 200,000 miles on the clock, its time for a cleaning anyways.

I have considered a possibility that because of the bumps and broken roads that the car's accelerometer (which is used to differentiate between a engine knock or the car hitting a bump) could be faulty, but it does seem like the culprit.

Tapsa · Post by **Tapsa** » 19 Feb 2009, 01:22

Hi,
I had this kind of ramping up idle and dropping low few years ago. Explained it to myself being computer trying to find optimal mix but failing. Cause was leak in air intake side. Mine was getting worse as engine was warming up and finally found the leak in air intake manifold gasket after it's over ten years untouched operation.
br Tapsa

hendricksl · Post by **hendricksl** » 20 Feb 2009, 00:51

I have checked all the plugs, wires and coil. All is good. Cleaned the throttle body and intake to include the MAF sensor. Still has been runnung great but it still hasnt rained so we will see. It only does it after a hard rain or when I hit a big mud puddle then the idling problem stays for two days and then leaves.

Craigd2599 · Post by **Craigd2599** » 20 Feb 2009, 08:22

did you pull your ecu's and see if the box is cracked? You have water getting somewhere it doesn't belong