I've searched all of the 740 postings that I can find here and elsewhere but no one seems to have the same problem I'm having so hopefully someone can help. I've got an 89 740GL non-turbo that starts great hot or cold but stalls. After initial start the idle is smooth and stable but if I tap the throttle and let go of the gas the rpm would drop too low to even register on the tach, and all of the lights would come on, then the engine would stall. If I keep the gas on I can rev the engine to 3000rpm and it'll run just fine. No misfires or hesitation. From there it'll stall if I let go of the gas. The Check Engine light never came on because of the stalling. I did notice that in cold starts the idle doesn't rev up to above 1000 like it used to during warmup. I checked the IAC valve and it works outside of the car powered with the battery. I checked to make sure that the wire harness for it gets 12V power. There are no vaccum leaks that I have found. The car also idles and revs better with the Air Mass Meter plugged in than not. It's weird, though, that with the Air Mass Meter unplugged the car won't stall when I give the gas quick taps. Any thoughts would be appreciated.

 

Sounds like you need to clean the throttle body and adjust the throttle position sensor.I would try that first.If you have never adjusted the tps just clean the throttle body first and see what happens.When you had the idle motor out did you clean it?If not do so aswell.
The reason the car doesn't stall with the massflow sensor unplugged is because the computer goes into whats called limp home mode.Which is a reprogrammed mode that allows the car to still run pretty good.

 

Hey, thanks for the tips, tech. I first took the throttle body out and flushed it with carb/choke cleaner. This made the engine not stall out and it behaves fairly well with the tranny in park or neutral. I can blip the throttle and it won't do weird things. With the tranny in gear, though, and I give it some gas (brakes applied) the rpm goes up, comes back down to around 700rpm idle for a couple of seconds, then takes a dive to 300-400rpm. The car would shudder real bad but no lights would come on, and after a few seconds it'll recover back to around 700rpm. This is at around mid 60s temperature. I'm afraid during the hot summer weather this would just stall again. Any ideas as to what could cause this weird dip? Oh, I did check the tps and throttle linkage adjustments and they were alright. The IAC I did clean when I had it out of the car, too.
Also, I was trying to locate the idle adjustment screw with no luck. My Haynes manual says it should be on the underside of the throttle body but there was nothing there. This is a California car, BTW.

 

Usually that takes care of the problem.On a hot summer day you will probably have the A/C on and the idle shoud be a little higher.When the A/C is on the idle uaually kicks higher.How does the plugs,wires,Dist cap,and rotor look?

 

Plugs, wires, cap & rotor are all less than 5000miles old. The weird idle drop and stumbling was annoying me big time so I kept checking and found a dead in-tank fuel pump. Ordered one so I'll know by next week if that's the reason for it.

 

Good find let me know how you make out.[sm=smiley20.gif]

 

Yep, that in-tank fuel pump was the problem. The car's back to normal now with a new one whirring away in there. When I was testing I did notice that the car will run with just the main pump. I wonder if my in-tank pump had been dead awhile and the main pump was starting to get real tired before the stalling symptom started. Maybe I should replace the main pump in the near future before I get stranded somewhere.

 

That might be a good idea but is very expensive.Glad it worked out fine.

 

I have been having a similar problem with my 89 240 DL. I tried spraying carb/choke cleaner on all of the vaccuum hoses to see if I had a leak. Problem is, I'm not exactly sure which ones are the vaccuum hoses. There are alot of hoses going in and out of the intake.
It has been stalling every time I let off the gas completely. It is usually better in Park, and as soon as i shove it into gear, i have to rev it to try and keep it from cutting out. Sometimes it works, and it gets a little spurt, other times, it just shutters and stalls... and all the dash lights come on.
It is very embarrasing at lights and stop signs.
I tried unplugging and plugging the air sensor back in... with no avail. I am going to have to unplug it to limp it home from campus (only a few blocks).

Any ideas guys?
Thanks in advance.

Mike

 

I have a 92 240 with a similar problem. Starts great, idels fine 800rpm A/C off and 950-1000rpm with air on. No stalls, but when you stop and move the shift lever from D to P it ether stalls or the "CHeck Engine " light comes on and then stalls. If you turn the key it will start right back up and run fine. I have cleaned the ISV and checked for vacum leaks and found none. any clues?

 

Have you tried cleaning the throttle body and idle motor yet?I don't think it is the fuel pump or the relay if it starts back up then most likely not a fuel problem.More like a sensor problem or a idle motor problem.

 

So do i just disconnect the hoses on the intake and spray carb/choke cleaner in there? Where is the idle motor located?
Sorry, i grew up in an auto body garage... but 3 years at college away from my own garage and not having a car on campus... i am a little out of touch.

Thanks for the suggestions... i will give it a try.

Mike

 

Remove the throttle body and clean it.The idle motor is located under the intake manifold.It is a silver cylinder with 2 hoses going to it.Take that out and clean good with carb cleaner.

 

Did you check the in tank pump to make sure it runs?