High Idle Issue Mechanic Can't Figure out issue

Relearns seem to work initially, but they don't hold. Goes right back to 1100 when you start it. Last mechanic replaced throttle body and did the batter cable thing. Truck still idles at 1100 in park/neutral. Still trying to figure it out.

 

It's been driven a couple days and still idles at 1100. Last mechanic replaced throttle body and did the batter cable thing. Truck still idles at 1100 in park/neutral. Still trying to figure it out.

 

Last mechanic replaced throttle body and did the batter cable thing. Truck still idles at 1100 in park/neutral. Still trying to figure it out.

 

Have you tried unplugging the MAF sensor yet?

 

Does the 4.0l have a throttle position sensor like the 3.4l? I know my nephew had and issue with his and it was giving the same exact issue you’re describing. Perhaps that is the issue?

 

I asked my husband, before we brought it to the mechanic he said he unplugged it but it didn't do anything from what he can remember. He has not tried it since we've had it back. The mechanic did test it and said it's testing fine. They also did diagnostics to make sure everything was working properly and said it was checking out fine.

 

I'm not sure, but the entire throttle body has been replaced with a OEM one. Made no difference.
It's so odd that the the idle relearn takes, but the minute you shut it off and back on it goes right back to 1100 rpm.

 

HAVE THEY TESTED THE ALTERNATOR VOLTAGE OUTPUT?

 

Do you have a scan tool? I have an inexpensive, 20 dollar inexpensive one from Amazon. Doesn't do everything, i.e. no tpms access, but it's does what I need.

I also paid for the torque app. This app lets you make gauges. Make a bunch... MAF, TB position, AF/O2 sensors, short term fuel trims.

Start logging everything and go for a drive. Review what was logged. You'll probably find something that's off.

For example; I had a P0420 code, basically a bad cat. My O2 sensor for that side was all over the place. I eventually found a tiny spot of soot. I replaced the gaskets connecting the y-pipe to the cats and everything was normal after that.

A lil patience and perseverance, and you'll find it.

Seriously, the scan tool will pay for itself, the first time it helps you figure something out.

 

are you making sure the truck is getting up to temp? If it does not reach operating temp it will not idle down. (dont look at the dummy gauge on the dash, im talking actual reported temp via OBD)

 

No idea.. I will find out.

 

Yes we do have a decent scan tool, forget the name bought it a few years back for $200 something. We have no codes at all.

 

Yes vehicle is up to temp.... drove it for a long time and at high speeds to make sure it was. Thanks.

 

Doesnt mean it was up to temp. You could have a stuck open thermostat not allowing it to get to temp. Thats why i stated look at an OBD output temp of actual degrees. 7 dollar bluetooth OBD reader and the free torque app on your phone goes a long ways.

 

We have a scanner and the scanner showed up to temp.. I meant we drove it a while to get it hot then checked the scanner.

 

Maybe a faulty CTS (coolant temp sensor) too.

 

So new throttle body. Supposedly there are no vacuum leaks and the MAF sensor is good. No IAC valve.

Have you looked at any of the O2 sensors or tried adjusting the throttle cable itself?

 

On your scanner, can you watch fuel trims while driving, and idling, once up to normal operating temp?

Can your scanner show if you are in Closed loop, when up to temp? Or does it always stay in Open loop?

Can you see the AFR for each bank, as well as O2 for each bank?

Can it show Throttle position ,and pedal position?

Can it show if the MAF is reading properly?

Do you have any aftermarket intake/exhaust components?

Do you have any pictures of the engine bay?

 

I've heard you can't adjust throttle cable as it's drive by wire? O2's aparently scan out good.

 

I don't have the scanner in front of me, recollection says that you can see open/close etc. Is it a mechanics scanner no, but it's not a $25 scanner either. However the mechanic also put this on their scanner. I don't have a picture of my engine bay at this time as I am at work.