1984 944 Rough Idle and Smoke at Cold Start
 

So, I'm hoping someone can help with this issue.

Our 1984 944 is having the issue of a crazy rough idle and smoke at start up after sitting for a day or more. The rough idle can be overcome by increasing throttle, but it dies once the throttle is released. After it dies, the car won't start unless the throttle is held to the floor. It will eventually fire and run. Once the car is running, it seems fine. I can shut it down and go back hours later and everything is fine. It starts, idles and runs as it should.

The last time I had the issue, I shut it down and pulled the spark plugs. All four were black and wet with fuel.

I know that this all points to a flooded and/or rich environment. I have read other posts that point to leaking injectors flooding the cylinders while the car is sitting for a time. This all makes perfect sense to me, but I pulled the fuel rail and pressurized the system and didn't see any leaks. I also pulled the injectors and cleaned them. They all seemed to function properly. I would seem strange that all four could be leaking.
We've also changed the fuel pressure valve and done fuel pressure and leak down test that show acceptable results.

We've also changed the DME Temp Sensor.

Additionally, there is no sign of a head gasket problem.

I'm baffled and getting frustrated. The car runs great except for this occasional issue.

What do you think? I'd really appreciate any input.

Thank you.

Go to Clark Garage on the web. First test is to determine fuel pressure at the rail. Without data, my first guess is the fuel pressure regulator failed closed, high fuel pressure above spec You can do tests per Clark or change parts at random

Thanks for the reply.

I have been using Clark's Garage for years.

The car has a new Fuel Pressure Regulator and the pressure tests check out fine.

That is why I am here looking for help. I've done extensive research and testing, but I've reached an impasse.

When you say cleaned the injectors, please provide clarification on who and how cleaned.

Thanks again for going over this with me.

I cleaned the injectors using pressurized carb cleaner and pulsing the injectors. I flushed them in both directions.
Also, when I put the injectors back on the fuel rail, I pressurized the fuel system and looked for any leaks before I mounted them in the head.
There were no leaks.

Another development with the car happened this morning. It fired up with no issues this morning, so I decided to drive it to work.
I got about 5 miles, and it just died. I coasted to a parking lot and tried to restart it. No go. I could smell plenty of fuel, but nothing. I also felt the DME relay as I turned the key on and as the engine cranked.
There was clicking in the relay in both instances.
We towed the car home, and when I got home a little while ago, I tried the car again. It fired up and did the rough idle and smoke act. I decided to hold the throttle up for a little while to see what would happen.
After about 3 or 4 minutes, the idle instantly calmed and everything seemed fine.

I'm baffled. I'm wondering if it is a DME issue.

From my experience, the fuel injectors need to be disassembled, ultrasonically cleaned, and then reassembled. Southbay Fuel Injector Service tested my fuel injectors prior to cleaning for a benchmark, disassembled and ultrasonically cleaned, reassembled, and tested with a before and after report. The cost was less than $100 including shipping. Southbay has a website and their customer service is excellent.
If it was my call, Southbay cleaning and testing is going to remove one big frustration.

I appreciate the input. I'll look into Southbay.

Thanks

guytranspo,

Sorry, but I don't have any useful suggestions for you at the moment... however, I am having a similar issue and am very interested to know if you find a fix for your problem.

My 944 was doing fine.. then suddenly, it started acting up with a very rough idle..which would resolve on faster throttle settings. Sometime, Often, it will start and run normally, with no issues. Occasionally, it will
Start running rough, and then smooth out after 5- 10 minutes. Once I drove to a store about 4 miles away, and it was running rough... then, when I came out, after about 10 minutes, it started and ran fine. This is a very puzzling problem because it's very unpredictable so far.

I haven't really spent time on trying to solve this problem but hope to in a few weeks when it warms up in Chicago (my garage is unheated), so I am very interested in the resolution you come up with.

Of course I'm wishing you good luck in getting a solution.

Best

WC944

Thanks for the update... I . certainly hope that is the fix for you.. ... ... fingers crossed for you.
Cheers!

You might also want to check the throttle air bypass valve. It is supposed to be open at the start, then close off after engine warms up..about 5 minutes. If it's stuck shut or only partially open that could result in arough idle and rich running. It has two connections, one is positive, the other, ground. remove the valve, apply 12 volts to it with some jumpers and peer down inside with a flashlight...watch the valve open and close slowly. It may just need cleaning also. Glad to hear that the cleaning of the DME made some improvement! Good to know!! Thanks for the additional option!

How long have you had your 944? At what RPM do you normally shift, and at what RPM does your engine normally run?