Idles high when transmission is in neutral and in park?

Hi,

How high is the idle speed? Also, have you checked to see if there are diagnostic trouble codes stored in the computer?

This vehicle has an OBD1 system that doesn't require a scan tool to retrieve codes. All you need is a short jumper wire or even a paper clip.

Here is a link that explains how to retrieve codes:

https://www.2carpros.com/articles/buick-cadillac-chevy-gmc-oldsmobile-pontiac-gm-1983-1995-obd1-code-definitions-and-retrieval-method

Try this and let me know the results. Also, let me know if you have checked for engine vacuum leaks. Additionally, confirm there is nothing binding on the throttle cable preventing the throttle plate from fully closing. See pics below

Let me know what you find.

Take care,

joe

See pics below.

Hi,

Code 34 is related to the manifold absolute pressure sensor (MAP). That could be causing the issue.

I attached the diagnostics below for code 34. Take a look through them and let me know if you are comfortable performing them.

Also, I attached a pic showing the location of the MAP.

Let me know what you find.

Take care,

joe

See pics below.

Hi,

Is the same code still present? If it is, are you comfortable performing the diagnostics above?

Also, this only happens in park or neutral. When you place it on gear, does it idle down or does the load on the engine simply slow it down? If you have it in gear and take your foot off the brake, does the car go on its own?

Let me know.

Joe

Hi,

Okay, if you haven't already, check and confirm there are no engine vacuum leaks.

Here is a link that explains how this is done:.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

If there are no leaks, take a look at the directions for idle speed adjustment. Since you already replaced the IAC, follow the directions where it discusses relearning the IAC. It starts with the number 6 toward the end of the pics.

Let me know.

Joe

See pics below.