RJB

After searching the archives and doing everything suggested there, I still have a question.

Symptoms: When the engine is cold (about 5 minutes after starting), I get hesitation in acceleration in 2nd and 3rd gear. After it warms up, then there is no hesitation. The idle seems to hunt between 750 and 900 rpm after the engine warms up.

What I have done: Cleaned all of the grounds, replaced the air filter, tested and cleaned the AMF, cleaned the throttle, cleaned and adjusted the TPS, cleaned the throttle bypass valve, replaced the spark plugs, checked for vacuum leakage, checked the spark plug wires, checked the rotors, cleaned the connectors to the speed sensors, replaced the DME relay, and cleaned the DME connector.

Here is my question. Does this sound like an O2 sensor or an engine temperature sensor problem? If so, does anyone know how to test these parts?

Thanks, BTW the pun was intentional!

944 Fan

It is going to be one of the following. (1) You need a new tps sensor. Cleaning the throttle and adjusting the sensor does not always work. You might have to replace the tps sensor if it is the original or very old. (2) You need a new idle control valve. Cleaning this does not always work either. (3) You need a new oxygen sensor.

I had the same problem. I ending up replacing all three and the problem went away. The idle went up and down from 750-950 during the cold months. Summer it was fine. Had a good idle when first cold, but then when warm it idled like crap.

It's difinitely one of the sensors listed above. I can almost guarantee it. You will probably have to do it by process of elimination. Unless you know how to test them. I would start with the tps sensor, since it is the cheapest and most common to failure. Then the oxygen sensor. Then the idle control valve.

If you want a rock steady idle, then replace the spark plugs, the spark plug wires, and the cap and rotor as well. Then i can guarantee you won't have any problems with your idle any more.
But you will definitely be out of money.

Just remembered something on my 86 944. Check your intake boot for cracks or leaks. This also caused a hard idle on my 86 944. Replaced and engine was smooother running.

Good luck!!!!

Danno

"The idle seems to hunt between 750 and 900 rpm after the engine warms up."

A hunting idle is a sure sign of a vacuum leak after the throttle body somewhere. This extra air causes the closed-loop O2-feedback to continually play catch up with increasing fuel to match the leak, then it gets too rich and drops the idle, then lean to compensate for lower flow, then richen to catch up to leak, etc....

Every single one of those hoses under the intake manifold is suspect. Especially the Y-connection at the venturi....

led

What's the idle rpm supposed to be? My car currently idles at about 1000, too high?

Robert D

My car has the exact same symptoms. I am about to replace the TPS....if I can figure out what is making the fuel pump fuse blow.
I have already replaced the idle stabilizer and O2 sensors. Cap/Rotor as well.
-Robert D.

Mike B

Robert, Did replacing the idle stabilizer and O2 sensor make any difference at all...and did you use new parts...

RJB

Thanks for the advice. I am going to check the vaccum again and will replace the O2 sensor. I will let everyone know the results. It might be a couple of days until I get the sensor and the tools necessary to replace it.

Thanks. Everyone on this board is great!

Thom

[quote]Originally posted by led:
<strong>What's the idle rpm supposed to be? My car currently idles at about 1000, too high?</strong><hr></blockquote>
The worskshop manual suggests 840 +/- 40 rpm on any NA 944.

led

so, how can I lower the rpm?

Robert D

"Robert, Did replacing the idle stabilizer and O2 sensor make any difference at all...and did you use new parts..."

Yes, I used brand new parts when the head was rebuilt. The biggest difference now is I can hear the idle stabilizer working, and the car will idle smooth then cycle to rough once it warms up. Seems like it is fixing itself, then screwing up, then fixing itself.
It still drops to low RPM when i let off the gas from say about 1500rpm.
-Robert D.

Mike B

Thanks Robert...I have a similar idle problem, which recently developed, where the idle fluctuates from 1000 to almost stalling...In fact it will stall if I don't gove it extra fuel when waiting at a traffic light...Really pisses me off as it was running great after I rebuilt the motor and then this pain in th a$$ developed...

Since I have to remove the intake (again ) I plan on replacing the Idle Stabilzer and all the vacuum hoses...Don't want to pull the mother off again...Then the 02 sensor then the TPS...If it doesn't purr like a kitten then it's off to the crusher