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

[SalvadorP]

So, in portugal it hasn't been raining lately, but today it is. I drove the car and like usually (or always), when it's wet/rainy, the car idles like crap.

Symptoms:

- Idles at 1500rpm when rainy and vibrates
- As long as the car is moving, even if disengaged, the idle is at 1500. As soon as it comes to a full stop, idle drops to 950rpm, like usual.
-Car always has a slightly fluctuating idle ate 950/1000rpm, even when dry.

Any ideas of what may cause these symptoms under these conditions?
Leads and plugs are new, rotor and cap seem (to me) to be fine. MAF is suspected to be malfunctioning. Idle valve is untested. Alternator is untested.

[tofufi]

How reliable is the speedometer?

The speedometer is powered from a speed signal from the rear differential. At least on the turbo models, if the engine ECU isn't getting this speed signal, it can put it into a fault mode and idles approx 1500rpm after the car has been driven on boost.

If the speedometer is OK, it could be a poor signal from an engine sensor of some sort.

As you have a late car, it should have some form of OBD. No idea how to use it though there are threads on here about using the OBD system

P.S. My brother's 940 has a similar mileage to yours! 2.3 LPT auto... (nearly 310,000 miles!)

[griston64]

Originally Posted by SalvadorP

So, in portugal it hasn't been raining lately, but today it is. I drove the car and like usually (or always), when it's wet/rainy, the car idles like crap.

Symptoms:

- Idles at 1500rpm when rainy and vibrates
- As long as the car is moving, even if disengaged, the idle is at 1500. As soon as it comes to a full stop, idle drops to 950rpm, like usual.
-Car always has a slightly fluctuating idle ate 950/1000rpm, even when dry.

Any ideas of what may cause these symptoms under these conditions?
Leads and plugs are new, rotor and cap seem (to me) to be fine. MAF is suspected to be malfunctioning. Idle valve is untested. Alternator is untested.

Your idle should be 750rpm so it's high to start with. Have you cleaned the throttle body and adjusted the throttle position sensor ?

[griston64]

Originally Posted by tofufi

How reliable is the speedometer?

The speedometer is powered from a speed signal from the rear differential. At least on the turbo models, if the engine ECU isn't getting this speed signal, it can put it into a fault mode and idles approx 1500rpm after the car has been driven on boost.

I imagine the 1500rpm idle is a fault mode intended to ensure the engine keeps running, so if the speedometer is OK, it could be a poor signal from an engine sensor of some sort.

As you have a late car, it should have some form of OBD. No idea how to use it though there are threads on here about using the OBD system

OBD port is in the armrest but you need a homemade reader for it.

[SalvadorP]

Originally Posted by tofufi

How reliable is the speedometer?

The speedometer is powered from a speed signal from the rear differential. At least on the turbo models, if the engine ECU isn't getting this speed signal, it can put it into a fault mode and idles approx 1500rpm after the car has been driven on boost.

If the speedometer is OK, it could be a poor signal from an engine sensor of some sort.

As you have a late car, it should have some form of OBD. No idea how to use it though there are threads on here about using the OBD system

P.S. My brother's 940 has a similar mileage to yours! 2.3 LPT auto... (nearly 310,000 miles!)

I have a homemade tester and I read the car a while ago. There was a code but can't remember which. I have to look on the forum, because I posted it.

Originally Posted by griston64

Your idle should be 750rpm so it's high to start with. Have you cleaned the throttle body and adjusted the throttle position sensor ?

I have cleaned the butterfly and it wasn't dirty/greasy at all. I have not adjusted the throttle position sensor and do not know how to do it. It's a screw on the throttle body?

[griston64]

https://mail.google.com/mail/u/0?ui=...tt&disp=inline

[tofufi]

Originally Posted by SalvadorP

I have cleaned the butterfly and it wasn't dirty/greasy at all. I have not adjusted the throttle position sensor and do not know how to do it. It's a screw on the throttle body?

The third post here details the procedure, points 3 and 4 are adjusting the TPS itself:

https://turbobricks.com/index.php?th...needed.301882/

It's just a switch on the throttle body which tells the ECU when the throttle is either closed, or wide open. You should hear an audible click from the switch when manually operating it.

Not an unusual item to go wrong with time.

[SalvadorP]

Found it. At the time I was just chasing the wondering idle/rythmic misfire. But the car already showed this symptom of high idle when humidity is high.

The car was throwing these codes back then:

3-2-2 on pin number 3 which is maf related
1-2-2 on pin 13 which is cruise control

[SalvadorP]

Originally Posted by griston64

https://mail.google.com/mail/u/0?ui=...tt&disp=inline

this link gives me an error

[SalvadorP]

Originally Posted by tofufi

The third post here details the procedure, points 3 and 4 are adjusting the TPS itself:

https://turbobricks.com/index.php?th...needed.301882/

It's just a switch on the throttle body which tells the ECU when the throttle is either closed, or wide open. You should hear an audible click from the switch when manually operating it.

Not an unusual item to go wrong with time.

Not sure I understood the part where it says: "turn the TPS counter-clockwise (toward the connector) until you hear or feel a "click". Continue turning until IT stops,"

Until what stops?

The screw was definitely way to high/long. I shortened it a bit, and messed around with the TPS until it was idling lower, I guess about 800. But it still fluctuates/misfires!?/idles like crap. The car also vibrates even more at lower idling speed.