Have been scratching my head and using Search to find answers here and at other forums. Leaving me with more questions than answers!

1987 245 with M47 about 250k miles, reasonably well maintained.

Symptoms: Car starts and idles without issue. While not in gear, the moment the gas pedal is touched to apply throttle, the car shuts off. There is no stumbling/stuttering. It turns off like a switch.

These symptoms persist in spite of the following diagnostics:

- confirmed working fuel pump relay/main pump
- disconnected the MAF (and cleaned it) without any change in symptoms
- cleaned throttle body - confirmed “clicking” as butterfly moves - cleaned TPS contacts and tested good with ohm meter
- cleaned/tested idle air control valve
- checked for/and found holes in the accordion air intake hose - temporarily repaired them with tape while waiting for replacement to arrive
- checked for other vacuum hose leaks - none found
- checked grounds, all show continuity

Symptoms persist. Car will start easily and idle fine (slightly high RPM/1000 or so) but will die/shut off the moment the gas pedal is depressed. Turning the throttle linkage by hand can raise RPM as if the car were accelerating, so the stall only occurs when pressing the gas pedal.

Any help is MUCH appreciated!!

The number of systems (and wires, connections, etc.)you need to search through could be reduced if you can narrow the problem to ignition or fuel. Try holding a plug wire near the plug so you can see the spark jump. Then have someone operate the gas peddle. If you have a multimeter or test light try monitoring the 12V connections at various ignition and fuel devices. You could also do this at the fuse panel.

Hi,

There is a definite answer in here somewhere we just need to listen to what the car is dong.

An increase in load of any kind should raise the idle the rpm. Loading shifts of a tiny bit like an electrical load of charging the battery or like when the battery cannot supply enough back up juice.
Some are so subtle you would never think of it but the Idle Air Control motor is working all the time at idle.

The next clue is to notice is when starting the engine does the idle race upwards to about 1200 to even 1500 and then immediately fall back down?
If it doesn’t do that, the problem is with the IAC. The engine in stop mode the ECU will command a full open IAC upon first crank.
You should never have to touch the throttle or the pedal for the car to start. It’s best not too!

Now the IAC is controlled by the ECU from the beginning. Do not move the throttle as the throttle switch gives the ECU a signal that the throttle is closed for the engine to idle.

If the throttle plate is too far open then the IAC is out of the picture and letting in too much air.
A big problem if it’s out of adjustment or the accordion hose is split.
Having a spilt in the accordion hose will let in more air above the operating range of the IAC.
Tapind may or may not work but several thin coatings of liquid electrical tape can do a better job in a pinch. You gotta keep that hose away from a fender or things that can rub it.
Replacement is the best option and you are on to that.
The hose can cause an erratic idle or even a sudden stall out.
The higher idle than the absolute 750 rpm required is also a clue.
So both items have to work together to give the ECU a heads up that “the driver” is changing the program.
This is from idling to powering up.
If the transition period gets out of step while the ECU is running a program other things others things may get used in conjunction for adding power that comes from the ECU program. Timing and fuel rates mix up around information from the AMM.

Unplugging the AMM starts another “limp home” program.
That’s like putting another cook in the kitchen or mechanic under the hood tweaking things.
It’s not a definitive troubleshooting technique, at all, but can make you decide that having a know good one as a spare as a better technique.
It’s possible to be an AMM as last three digits on the early LH AMMs changed over the years.
The 1987 maybe be at a mid-life crisis but there too many other factors in play here.

I think you have been doing all of the right things but may not have enough information on what to expect during certain time of start, warmup and operating temperature sequence.

The other cook under the hood keeps its lips shut but uses sign language. 👋🏻
Codes on the nineties cars are not much help so don’t get too wanting those over what you have.

A sticking or non working IAC sneaks up on you.
To the credit of most of the posts it’s appears to be a air regulation problem since it starts and runs reliably.

Think and listen to the sequence’s of the components and then follow the rose pedals.

Phil

You said you disconnected the AMM and cleaned it. Did you try running it with the wiring disconnected? Try that, if it starts and runs rough, but also accelerates. The problem is the AMM.
--
Bruce S. near D.C.

Weird one indeed. The key symptoms are you can raise rpm normally turning the throttle spindle, but it immediately dies if you depress the gas pedal. There are no components on the pedal assembly other than cable going through the firewall to the spindle. Movement at the pedal assembly is likley causing an electrical problem in the wiring around it. If it was a short to metal you'd likley blow a fuse. My best guess is a loose wire above the pedal mechanism affecting the ignition switch wiring. With the engine idling, you may want to try selectively moving a few wires above the pedal and behind the ignition switch to see if you can isolate the errant connection. You'll then want to inspect that whole area with good lighting and maybe also a mirror to find the damaged or loose connection, most especially the wiring at the back of the ignition switch.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

Hi,

You have an intriguing problem there.
It's surprising that any movement of the gas peddle kills the engine,
but increasing RPM works by hand.

Maybe you have some issue with the peddle linkage chaffing against some wiring? I'd give that a look.

You can have a faulty sensor connector:
You can go back to your AMM, and TPS connectors and see if the harness
connectors are OK. You don't want any signs of corrosion or damaged or
deformed pins. Use some Penetrox ,dielectric silicone, or silicone spray
on the connector pins on reassembly.

Reset the ECU's , unhook the battery for a minute. See if that helps.

Good luck, Bill

Thanks very much!

Apologies, but I forgot to add in the first post that at idle, turning on the a/c and/or blower will also cause the car to stall out.

And, correction: manually turning the throttle linkage can result in revs without stalling, but you have to feather it gently. Otherwise if you just turn it quickly it also stalls out.

Tried disconnecting the battery for a bit and also checking grounds again.

No change in symptoms!! 😵‍💫

Hi GLT?

I'm a rookie at 240 schematics but I see something in the 85 240
schematic, undefined, between the battery + and pin 30 of the ignition switch.
Is that a fuse?
If so pull it out, shine it up with scotch bright and put
some Penetrox, Copper anti seez, or dielectric silicone on it.
Shine up the fuse holder and reinstall the fuse.

Bill

Thanks very much!

Apologies, but I forgot to add in the first post that at idle, turning on the a/c and/or blower will also cause the car to stall out.

And, correction: manually turning the throttle linkage can result in revs without stalling, but you have to feather it gently. Otherwise if you just turn it quickly it also stalls out.

Tried disconnecting the battery for a bit and also checking grounds again.

No change in symptoms!! 😵‍💫

Hi again ?,

Putting additional current load kills the` works?

Service the battery terminals especially the smaller positive #10 Ga wire.
Maybe you have some cruddy connection there. Check for loose/corroded
crimps etc.

Bill