'91 940GLE auto hot stalling

bobbyz · Post by **bobbyz** » 04 Oct 2008, 12:38

Threw a 2-3-2 code.
Replaced fuel filter, plugs, checked flame trap & hoses (no trap found & no clogging), clean the air mass sensor, checked throttle body (clean).
Cleared the code, but came back again.
Sprayed water at intake manifold gasket area, but no change in idling.

Problem only starts when engine is warm: after some city driving, I stop and do some shopping. Came back and start car. Car starts fine (after 5-7 cranks), but it just wouldn't idle, as if fuel supply is turned off after startup.
I have to lightly touch the pedal to keep throttle ajar so engine can stay running (around 1k to 1.3k rpm). If I keep it for about a minute, then it idles, but rpm still fluctuates a little. During that minute of forced idling, I could feel the engine hesitates. It wants to die but can't because throttle is open.

Also, when engine is warm and I brake hard, it also stalls half the time. But I notice that moments before coming to a stop during braking, if rpm doesn't drop all the way to 0 (stalls), it would go back up to normal idling value (~750rpm)

I pulled the vacuum hose off the fuel pressure regulator, it's dry & has no gas smell.

Any advice is greatly appreciated!

DeRail · Post by **DeRail** » 06 Oct 2008, 21:23

If you unplug the MAF sensor and try to start the car, what happens?

When you unplug it, the car goes into "limp" mode where if I understand correctly, the mixture isn't adjusted by the ECU but instead a default setting is put in temporarily. You can't drive for an extended period like this, but you can try it for testing.

Also, check the vacuum line running to the brake booster

good luck

wojeepster · Post by **wojeepster** » 07 Oct 2008, 15:34

clean your idle air motor

bobbyz · Post by **bobbyz** » 07 Oct 2008, 22:50

Thanks for the reply DeRail & wojeepster.

Will check the MAF, vacuum lines and idle motor.

Lately I only use the car at night.
Did a few highways, starts & stops. Car idles fine so far, though hard stops from higher speed can still cause rpm to dip way below 500, in which case I sometimes need to release the brake just to let the rpm back up a bit.

bobbyz · Post by **bobbyz** » 09 Oct 2008, 22:45

CRC-Sprayed the MAF.
Checked the brake and intake vacuum hoses. Nothing cracked or loosened.

btw, I checked the rpm sensor and found its insulation torn at both ends. Not sure if it's the cause of hot stalls, but I replaced it anyways.
I also replaced the fuel pump relay.
Will know in a few days if the problem is gone

bobbyz · Post by **bobbyz** » 14 Oct 2008, 23:23

Problem still there. After hours of city/highway driving, stopped the car & went away for like 20 minutes. Came back & start the car. Starts OK but I need to press the throttle a little, or rpm will fall back to 0. Car still idles like crap at traffic lights after I took it to the road. But after like 10 minutes, the idling problem is gone again.

Checked the IAC. It wasn't too dirty to begin with, I cleaned it anyways. Applied 12V across it, the ring-type valve opens/closes.
Also cleaned the hoses connected to it.

Any other ideas what else to look for? Stalling only happens when engine is warm.

Post by **billofdurham** » 15 Oct 2008, 11:43

Check the throttle switch and its connector; inside distributor cap for burned segments or rotor; ignition and coil circuit for good, clean connections and coolant temp sensor and its connections.

Bill.

wojeepster · Post by **wojeepster** » 15 Oct 2008, 20:20

check accordian hose between air mass sensor and throttle body. sometimes they rub on the fender and get a slit in them allowing unmetered air in.

bobbyz · Post by **bobbyz** » 15 Oct 2008, 23:26

billofdurham wrote:Check the throttle switch and its connector; inside distributor cap for burned segments or rotor; ignition and coil circuit for good, clean connections and coolant temp sensor and its connections.
Bill.

Thanks for the advice Bill. Is there a diagram available showing the location of the coolant temp sensor?
I looked underneath the intake manifold and saw 3 sensors:

The first 2 (with white & blue connectors) face the engine, and I think there's a 3rd one (indicated by arrow) just underneath the 2nd (blue connector) one, but this one faces a different direction (towards the fire wall)
Which one is the coolant temp sensor?

Post by **billofdurham** » 16 Oct 2008, 12:01

There are two coolant temp sensors. One goes to the instrument panel gauge and the other to the ECU.

The wiring for that going to the gauge is yellow/black and yellow/white.

The wiring for that going to the ECU is grey/white and red/black. This is the sensor to check as it helps to control the engine.

The third sensor is the knock sensor.

Before testing the sensor ensure the ignition is off as damage may be caused to the ECU.

Disconnect the connector and connect ohmmeter leads across the sensor terminals. The resistance varies with the temperature of the engine.

At 14F (-10C) resistance should be 8,260 - 10,560 ohms.
At 68F (20C) resistance should be 2,280 - 2,720 ohms.
At 176F (80C) resistance should be 290 - 364 ohms.

Bill.