Idle high when rainy. Drops to 1000 when car comes to a stop

[V40onepointeight]

Originally Posted by SalvadorP

I have never complained of low mpg and I try to maintain my car the best I can with a knowledge I have and the help of the guys in the forum.
Nor am I against buying a new maf. I just don't want to buy a maf and then still have the problem. And maybe down the line realise it was a pin size hole on a hose afterall. One thing is to load the parts cannon with 50€ projectiles... If it's not that, well, you now have a brand new part. Another is to load it with a 300 to 500 bill. I would rather troubleshoot and replace cheap parts first.

You mentioned that the problem seems to happen when it's rainy. As any old wizzened washed-up engineer knows, damp air has less mass than dry air. That could also be a pointer that your MAF is the culprit. As an aside, have you cleared the ECU and seen if there's any difference in performance?

[TonyS9]

Just on rain issue, It's more rainy in the UK and I have had the bonnet seal fail and drip on the distributor. But this causes severe ignition problems and engine dies when you try to accelerate hard.

Other than that the speedo can work while the vehicle speed signal isn't making it to the fuel ECU. The best way is to read the codes to check this out, but if the idle is dropping when you stop then it's probably OK.

You also want to consider an air leak, as this could be the reason for the high idle. It might be worse when it rains if its colder and you are getting more fuel from the cold start program.

[lynns hubby]

I had the same scenario as you several years back with my 940. I tried all the usual stuff you have been through. What was really frustrating is that the car drove fine in the dry. I even booked it in with a BOSCH tuning specialist who could find nothing. Obviously it would not do it in a warm dry workshop. I got to thinking about spray from the road whilst driving, so in desperation, on a dry day when it was idling fine up my drive, I got out a garden hose and sprayed underneath the engine. Bingo, it instantly started fluctuating and playing up. I traced the issue back to the wiring on the Lambda sensor in the front part of the exhaust. The wiring was beginning to break down and when water was added into the area shorting out somewhere. Initially the wiring looked fine but I changed the sensor for a new one and that cured that. Never had the problem again.
When I examined the wires closely from the sensors it was just possible to see the insulation starting to breakdown.
Its worth a look or even a change of sensor for a new one as I don't believe they are that expensive. Rules out another possibility if nothing else.

Good luck.

[lynns hubby]

Originally Posted by V40onepointeight

So you will have to live with the symptoms, the poor running and the high fuel consumption. Today I drove in 240 miles in very cold conditions down from the north of England in my 1996 940 2.3 HPT auto Estate and got just over 33 mpg with the car fully loaded. That's because the car is well maintained and set up.

In all fairness to the OP, it looks like this is all he is really trying to do. He is asking people on here with more knowledge and experience than himself for help, which after all is exactly what this forum is all about.