I’ve been daily driving my 944 for a little under a year now and it’s been pretty much flawless until recently it started feeling hesitant to accelerate and idling very heavy and sometimes it would just die. From my research this seems like a AFM issue but after swapping it out for another one I had laying around (not brand new and never tested to make sure it works properly) the problem didn’t go away. Does this sound like an AMF issue still or is there something I’m overlooking. If it’s something totally stupid that I’m just missing don’t be too hard on me, I’m just a high school kid trying to learn how to fix things.

 

Go to Clark's Garage website for ideas. Also use RL advance to find a zillion postings on this subject. The basics are air, fuel, and ignition on how these inputs are controlled by the ECU/DME. There are a few sensors that provide inputs to DME for also modifying the outputs from ECU depending on coolant temp, throttle body opening, etc. Sometimes the issue is with the wiring getting brittle or corrosion at disconnect plugs that affect the engine performance.

 

vacuum leak

 

leaking fuel damper, clogged injectors, improperly set idle...

Some of the many items that can cause stumbling issues. Firsthand experience.

 

First things that come to mind are a clogged fuel filter, failing or clogging injector or a vacuum leak. Also, how new are the spark plugs, wires, cap, and rotor?

 

OK, Mr Silly Billy, there is no such thing as a dumb question! So I think you need to remember your car is now 35 years old and all the rubber hoses are suspect. They will be hard and start forming small cracks that allow air leaks or fluid leaks. Air leaks will affect the idle the most. Look at all fuel hoses because a leak there is a fire hazard. Check all the filters, any older ones should be replaced, there are some good fuel injector cleaners you might try, but nothing beats pulling the injectors and having them reworked. Plug wires go bad with use due to the breakdown of the carbon cores and should be replaced every few years. Start planing for a Saturday project, and get a new hose or part then spend Saturday mourning putting it on. You do not have to do everything in one weekend, just make sure it is something you can finish in one day.
Look up how to test for air leaks, that would be my first guess. And you need to test the AMF in another car to see if the symptoms move to that car.
Good luck, you have great car to learn on.

Dan

 

I agree with @dhs928, if you are a high school guy looking to improve your skills and knowledge, on a 35 year old car, you unfortunately need to suspect everything. Fortunately what you are experiencing does not keep you from driving the car. It is tempting to troubleshoot and go immediately to the source of the problem. Paid mechanics need to do that and have the skills. You instead are in a learning mode and can afford to go down some dead ends. Reading the recent thread by @alcantor will be instructive as to how hard it can be to identify problems. But don't let that discourage you, none of us knew jack$hit about cars when we started out. It's a learning process.
My only advice would be to purchase a copy of Bosch Fuel Injection and Management- How to Understand

It covers a wide variety of 80's FI systems. Read it cover to cover, not all applies to your 944, but it is the best book I have found to help you understand how the various components work.
Good luck and feel free to ask questions. As with Alcantor, you will get plenty of help.
Harvey

 

OK, old fart forum guys, remembering how broke you were in high school, what are some things he can do that won't cost much to try?
My first suggestion- wait till it is totally dark outside, get your eyes adjusted to the dark, raise the hood, start the engine, and look around. I had a car once that looked like a small electrical storm with all the arcing from the spark plug wires.
My second suggestion- get some starting fluid and gently apply it to the various hoses downstream of the AFM. If you get an increase in idle rpm, you've probably roughly located a cracked or open hose, in other words a vacuum leak. Don't forget the hoses leading over to your brake booster. Hopefully, you still have the hose diagram mounted in your engine compartment. It is a schematic but study it and learn to find and trace the various components shown. So when we start talking about things like the fuel damper, you will know what is where.

And original poster, can we just address you as Billy?
And where do you live?
What shop tools do you have access to?

 

Hi Harvey,
The poster is @Acantor
Good to see your interest in 944's remains strong
Tom

 

The poster is @Acantor
How could I forget? It was a megathread!

 

Hi Harvey,
Age related??? How do you get the ellipse around the wording?

 

@T&T Racing
If you start typing with the @ symbol and then continue with the persons User Name it will prompt with valid user names. If you see the one you want and select it, it fills in the rest and adds the ellipse. This makes DOS Command Line prompts look positively archaic

I believe it also sends that person a notification?