Strange idle

[cathalp]

Today I noticed while stopped at lights that the revs dropped to normal,then the motor gave a clunk and revved up a bit and then went back to normal.
It's doing it in neutral too.
Sounds like some sort of governer.
Any ideas,I have 400 miles left on my warranty.

 

[Bryan22]

take it too ford before ur warranty runs out

 

[Wicked_Sludge]

+1

if you have warranty left, why mess with it yourself?

 

[cathalp]

I need it

I need it to bring me to Chicago tomorrow.
I bought it from a used car dealer,not a ford garage,so I know any repairs are going to take forever.
I can't afford to be without it if its something caused by low grade fuel or something stupid.
The Warranty is 1000 miles,I bought it last week with 137000 on it.

 

[Wicked_Sludge]

unplug the electrical connection at the a/c compressor and see if it still does it.

 

[KELLY88]

Check the MAF sensor and Idle Air Control for starters. You can test the Idle Air Control by leaving the engine idling and and unplugging that sensor. If your idle bogs down then the sensor is working. Its located on the upper intake, right behind the throttle body.

 

[Wicked_Sludge]

a bad MAF or IAC solenoid wont cause a clunk...

 

[Bryan22]

maybe, like when you don't get on the gas quick enough and let the clutch out too quick it'll knock real loud, like a clunk. a super low idle could be the sound he's talking about till the truck catches back up. . Cleaning the IAC and MAF couldn't hurt and dosen't take very long. worth the 4 dollar can of cleaner and a gasket for peice of mind at least. and is it more than a 400 mile round trip to where you're going and back? if not just take it in when you get back. If it turns out to be something major you'll really kick yourself in the ass for not letting the warranty cover it.

 

[sean9721]

When my A/C compressor turns on and off (it clicks) my idle speed changes by itself.

 

[cathalp]

Ac compressor

It sounded like something loading the engine alright. Hasn't done it today.
I hadn't the AC on last night. I had been doing a lot of stop and go driving.

 

[Wicked_Sludge]

the a/c cycles when you are in either defrost mode.

 

[cathalp]

Defrost mode?

When is defrost mode activated,and what does it do?

 

[greenlander]

IAC valve maybe?

I had a similar problem with my 94 XL--whenever I stopped at a light the engine seemed to be "searching" for its normal idle RPMs. Replacing the idle air control valve/solenoid worked for me. Easy fix--attaches to throttle body.

 

[Wicked_Sludge]

defrost mode is when you have the vents set to either defrost or defrost w/floor. it...defrosts the windows

 

[cathalp]

I see

I'm from Ireland. We don'r have to do much defrosting there.
And that's exactly what my truck was doing.
I switch the control to the windscreen and the AC compressor kicks in.
Thanks for all the help.