Mom-in-law's '88 240 DL
It drove her to work just fine but would not keep running when she wanted to leave.
Here are the symptoms as I see them.
There is spark, fuel & compression.
When the key it turned, it catches and then immediately dies.
Sometimes I can keep it running for awhile by giving it some throttle but not always.
When this happens, it runs very rough with what sounds and acts like multiple backfires into the intake manifold.
I removed the upper timing belt cover and the marks line up properly (cam gear marks & crank balancer marks). There appears to be some oil on the belt but there are no missing or chewed up teeth.
I considered the IAC valve but wouldn't it run OK with throttle and just have trouble at idle?
Car had tune-up in August w/new wires, etc.
Wires are hooked up 1-3-4-2.
There are no holes in the air intake hose that I have found nor are there any disconnected vacuum hoses that I can find.
I have not checked all the diaphragms yet to be sure they are sound.
I am now at a loss short of removing the timing belt parts and see if the key(s) is stripped.
Any other ideas?
Thanks in advance.
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Bob Kraushaar '94 945T, '91 940T(retired), '88 240, '84 242Ti, '94 F-150, '88 300TE, '89 560 SL, '68 Shelby GT-500 KR

Check the usual suspects:

Resolder the fuel pump relay (behind the passenger's side knee bolster pad, it's white with a date stamp on it, take it apart and resolder the connections), disconnect the AMM and see if it runs better (if so you'll need to replace it), check the 25 amp blade fuse and its related connectors and wiring in front of the engine coil and behind the battery, check for vacuum leaks (consider completely replacing all vacuum hoses if they look generally bad), make sure the throttle body, flame trap, and idle air valve are clean (though you are correct in your assumption about the idle valve - it's probably not that or the flame trap, but when you have the TB off it's a good time to clean the idle valve & FT, and if you've got oil coming out the front seals you could very well have a plugged up flame trap), and dress up all wiring connectors inside the engine compartment with some sandpaper and some dialectric grease.

Also change out your spark plug wires and dist. cap/rotor.

It sounds like a lot of work but really isn't if you know your way around, and it sounds like you do. If you've checked all these things and it's still happening, then post again.

If it is the AMM, then also check the thermostat for the air flapper in the air intake box. If that thermostat goes, the AMM goes. You don't want to shell out for a new AMM only to have it fry in a few months because a $15 thermostat was also bad.

AMM it is. Thanks for the info. As soon as it cools down, I'll check the flapper.
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Bob Kraushaar '94 945T, '91 940T(retired), '88 240, '84 242Ti, '94 F-150, '88 300TE, '89 560 SL, '68 Shelby GT-500 KR

Have the throttle body and flame trap been cleaned anytime recently? Might also want to check the airflow meter and its connections.
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85 245 DL - 91 Mazda MX6 Turbo

Hi, try disconnecting the MAF sensor/meter. start the car and see if
it starts/idles normally. good luck.