High idle when transmission is in park?

BASSDOUGHBOY

MEMBER
2000 FORD F-150
5.4L
V8
2WD
AUTOMATIC
180,000 MILES

I just started today, idle around 2,000 RPMs in park, but seems to run fine driving down road. When at a stop and on the brakes, it's around 1,500, in park. Turn A/C will cause it to drop a little.
Have removed connector from IAC and it drops to 500 or so, can find vacuum leak if there is one.

2 Replies

BASSDOUGHBOY

MEMBER
2 POSTS

I used a scanner and no codes, check the live data and it looks like everything is close to what it should be, Throttle sensor 20%, Fuel Rails within %, MAF at 2.2 when at 2000 RPM, not sure what else to check.

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Monday, July 24th, 2023 AT 5:32 PM

STEVE W.

MECHANIC
13,572 POSTS

First do a visual inspection of the lines and vacuum hoses and check the throttle body in case something is blocking it open a bit. That would also be a good time to clean the throttle body to be sure it hasn't carboned up.

https://www.2carpros.com/articles/throttle-actuator-service

However, being it was a sudden change I expect it's a vacuum leak. If you didn't find a cracked intake tube or bad vacuum line during the visual inspection the next step is to spray it. Take a can of carb cleaner and after the engine is cold, start the engine, now spray the cleaner at the various vacuum lines and at the intake and throttle body gaskets. Listen for a change in the engine and you have found the leak. I would suspect a vacuum line myself, that age the rubber is getting soft and starting the rot from the heat and age under the hood. You may want to wear gloves when doing the inspection and any repairs, the carbon black and rubber compounds they used then make a real mess if you get it on you.

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

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Tuesday, July 25th, 2023 AT 4:37 PM