Idle problem

[Hosana]

I have a 97 Mercury Sable with approx. 120,000 miles. It's been a good car except for normal user problems. However, it recently developed 2 new problems. FIRST PROBLEM is that it idles rough when put in gear, but fine when in park or neutral. When in park it has a smooth idle for a 11 year old car. When put gear the idle gets rough and has a speratic gargling noise. The rpm's fluctuate and the engine almost stalls out.

I took it in to the repair shop where they changed the fuel filter, cleaned the fuel injection system. They also said that this was a common problem that may require the internal computer to be reset. They couldn't do it until a later date, so I picked up the car and used it until the shop could reset it. After picking it up (SECOND PROBLEM) I noticed that the rpm and speedometer would maintain the speed and rpm's for about 3-5 seconds after I let off of the accelerator. When it would begin to lower, it would drop so suddenly that you could feel your body lean forward. Eventually, this problem stopped. I finally took it in to reset the computer (Ford Dealership) and all they could find was that the fuel/O2 mixture was a little off. No other codes. When I started driving the car again the rpm/speedometer issue started back again and lasted about a month. It still happens but not as severe.

Any idea on what could cause these problems? Any advise would be great!!!!!

Thanks,
Mike

[DistanceGuy1]

Do you know if the IAC [idle air control] valve has ever been replaced?

[Hosana]

I don't think it has ever been changed. What does it do?

[DistanceGuy1]

An idle air control valve is an electronic motor which adjusts idle speed. The valve is used by your car’s computer to change the amount of air flow.

It's a three wire system: a five volt wire, a ground wire, and a sense wire. The five volt wire is used with the ground wire to move the IAC motor. The sense wire is a direct line for the computer to monitor how far in or out the valve is. The position of the valve in or out is know as steps. The computer reads the steps and compares that information to the current idle speed of the engine. It can then determine how much to increase or decrease the engine idle speed. The computer can also adjusts the IAC to compensate for increased load on an engine. An example of this would be turning on the air conditioning.

It has a cone shaped tip called a pintle which protrudes into an air passage. The amount of air in this passage affects the engine idle speed. The pintle is on the end of a rod that has a spring around it. The rod is connected to the electrical motor which moves the rod and pintle in and out of a passageway. If the rod and pintle is pulled in by the IAC motor, the airflow is increased to raise the idle speed of the engine. The opposite will happen if the rod and pintle are pushed out. The airflow in the passage will decrease which in turn will lower the engine speed. They are not very expensive to replace [<$75 bucks] and most DIYers can do it rather easily.

[Hosana]

I can see how this could cause the bad idling and rpm problem, but how could this cause the speratic gargling sound?

Mike

[DistanceGuy1]

Your next step should be to see if any codes are stored...take your car to your local Auto Zone or other such auto chain type store; they should read it for free. Call first.