'98 Ford Taurus SE Idle issues

[ariester]

Hi Im new to the site and seeking some information on some issues Ive been having if anyone can help I would greatly appreciate it,
So first off when the car is cold and i start it, it tends to lurch forward almost like its still in gear. It then tends to shift a little hard into gear because the idle will linger high instead of idling down even when left to warm up for a bit.
Driving and shifting there is no real issue but I have noticed that while driving 55mph my rpms are around 2000 and when i shift into neutral my rpms actually go up to around 3000, and as i slow down with the car still in neutral the rpms drop accordingly until it bottoms out about typical idle speeds 1000 to 1500.
After the car is warmed up and i put the car in park just letting it idle, the rpms jump up and down like its about to kill the engine then back to normal idle.
Ive been reading all around the internet about different things but nothing quite fits my symptoms.
Thanks for reading and any input would be greatly appreciated.

[shorod]

Originally Posted by ariester

So first off when the car is cold and i start it, it tends to lurch forward almost like its still in gear.

Welcome to the forum!

You're not suggesting in the above quote that even when in Park, starting the engine will cause the car to move, are you? I assume you mean when you start the cold engine and shift in to Drive it lurches, correct?

If the former, then about the only thing that could cause that without other serious transmission concerns would be a really bad engine or transaxle mount. That could also help explain the harsh shifts when driving.

But it sounds more like your main concern is the high idle speed which would cause a surge when the transmission engages. There are several different issues that could cause the high idle speed. I'd suggest you start by checking for some of the free or inexpensive possibilities.

First, check the Intake Air Temperature (IAT) sensor to make sure it is still properly connected. If not connected, you'd likely have a diagnostic trouble code, but still worth checking.

Also confirm that your Engine Coolant Temperature (ECT) sensor is connected. Be aware that there are two coolant temperature devices, the sensor (used by the PCM) and the sender (used for the gauge). The sender won't impact how the engine runs, the sensor will.

Next, carefully inspect the engine compartment for any cracked, split, or missing vacuum hoses. As part of this check you'll also want to inspect the intake air tube for cracks, particularly in the accordion folds. If you have a vacuum leak the engine idle may remain high to prevent the engine from stalling. A vacuum leak could also help explain the fluctuating idle when the warm engine is shifted to park.

You will also want to consider cleaning the Mass AirFlow (MAF) sensor element with some MAF Sensor Cleaner. You will probably need a Torx Security bit to unscrew the MAF from the intake air tube. While in that area, consider cleaning the throttle plate front and rear.

If you have access to a fuel pressure tester, check the fuel rail pressure with the engine running and make sure it is in specification.

I'm assuming you don't have a scan tool since you don't mention the lack of any codes. But if you do have a scan tool, or have access to one, you can pretty easily monitor the ECT sensor values, the short term and long term fuel trim values (which will provide and indication of if there's a vacuum leak or not), and the Throttle Position Sensor (TPS) function over the throttle range. If the TPS has a worn spot it could cause a high or erratic idle speed as well.

Since you don't mention that the engine ever acts like it is going to stall or doesn't want to start I'm guessing you probably don't have an Idle Air Control (IAC) issue. It sounds like the IAC is working overtime though adjusting for some other issue.

-Rod

[65comet]

If you're not sure about any of the parts and locations Rod was mentioning, more information will be needed from you because there are more than one engine for that car. If you don't know if you have a Vulcan, FFE or Duratec, then at least get the eighth digit from your VIN.