2000 GT Engine revving when idling

My 2000 GT's engine revs up and down (from about 1500 rpm down to 500 rpm.. or less) when idling. Today it even stalled at a light. It seems to run perfectly fine otherwise. I first noticed this when I started the car in the morning to let it warm up, but it happens regardless of the engine temp.

Does anyone have any ideas as to what this could be?

Reply to
Lew Reid
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IAC sensor near the throttle body. Ford's renowned for not knowing how to make one worth a damn.

Reply to
Keith

You'd think after 15 years they could make one that works.....

----------------- Jim '88 LX 5.0 (now in car heaven) '89 LX 5.0 vert '99 GT 35th Anniversery Edition - Silver Mods to date - Relocated trunk release to drivers side, shortened throttle cable.

Reply to
AZGuy

Dunno....... ??

My 89 5.0 is doing the same thing.

Reply to
Katmandu

The check engine light comes on and goes off constantly in my '96. Computer is throwing a P1443 code. Checked my Chilton today and it says: IAC valve speed fault. All this time I thought/was told it was the gas cap! The idle does the same thing as Lew's, too. :-)

Is the IAC valve something you can replace?

Cindy '96 laser red auto GTS

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Reply to
C. Olofsson

First, I'd follow the idle setting procedure outlined in your manual. Disconnect the battery for 20min. and reconnect it and follow the idle procedure. That will take very little time and cost you nothing. If that doesn't work, I'd suspect the idle air control valve (IAC). It's the shiny thing right next to your throttle body. Sometimes a rap with a small hammer will loosen it up, but it's probably shot. Mine was ;)

Vic

2kGT 5m blk suspensi>My 2000 GT's engine revs up and down (from about 1500 rpm down to 500
Reply to
Victor DiMichina

Mine did that & something with my MAF was dirty so the shop used some special cleaning stuff to clean it out. This fixed it in my case.

-Mike

Reply to
<memset

Yes you can buy one from your local Ford Dealership and some auto parts stores sell em. Just go look around and try to find the best warrenty =)

Reply to
John Wiebalk

Bullshit! I've owned a bunch of Fords over the years and have put many hundreds of thousands of miles on them. I have NEVER has a single problem with an IAC. Of course if you don't have the throttle plate / idle screw adjusted correctly, you may THINK the IAC is malfunctioning.

LJH

95GT

Reply to
Larry Hepinstall

How does one adjust this correctly Larry ??

Reply to
Katmandu

That is not an IDLE set screw, never has been. It is called a throttle plate stop and is set to a specific gap. When the IAC is disconnected the engine should not idle. The IAC can be removed and cleaned using carb cleaner, I had to do this every few years on my '89 GT.

Reply to
Mike King

This is not an idle set screw, it is used to set the throttle plate to a specific gap. The engine should not idle when the IAC is disconnected. I still have the 2000 Ford service CD and I'll look up the info later. Any one that owns a 5.0 on the EEC-IV computer should own a copy of a book like this; (sorry, OE's gonna' cut it up)

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Reply to
Mike King

There is a throttle plate stop screw AND an idle set screw. The idle set screw is usually hidden under a protective cap near the IAC. If you have the throttle plate stop screw AND the idle set screw set correctly, your engine WILL idle with the IAC disconnected (but rpm drops about 200 rpm). The correct way to set this is measuring the IAC duty cycle and setting it between 12% and 24%.

LJH

95GT

Reply to
Larry Hepinstall

My bad, I should have said: If you have the throttle plate stop screw AND the idle set screw set correctly, your engine WILL and SHOULD idle with the IAC disconnected (but rpm drops about 200 rpm). If it won't idle with the IAC disconnected it isn't adjusted properly (unless you have a RADICAL cam that cant take a 200 rpm loss).

LJH

95GT

Reply to
Larry Hepinstall

The '89 only had the plate stop on the TB and should not idle when the IAC is disconnected. The computer controls the idle speed through the IAC, and when it's unplugged the engine idle should drop and then die within a few seconds. I'm not familiar with anything newer, I didn't have an idle problem with the '98 or '00 GT's. I'm also sure my Cobra only has the plate stop screw because there is a stalling issue being worked by SVT which requires a computer reflash. Some people have used the stop screw to bump up the non-A/C idle, then resetting the TPS to tolerance while waiting for the reflash. I'll find my '00 Ford CD and look up the idle set procedure, unless someone else does and posts first. I think the IAC just needs cleaned on the original posters 2000 GT.

Reply to
Mike King

I have a '91 Aerostar with 180K miles and a '93 Aerostar with 150K miles. I've also got an '88 Cougar with 300K miles. All of these vehicles had a problem with surging idle when the motors were cold, but cleared up after the engine heated up. On each of these applications, the problem went away IMMEDIATELY when the IAC was replaced. I know these are high mileage vehicles, but I have to agree that Ford is know to have IACs that fail after long periods of use. I didn't mind; the prices for the IAC valves are not that expensive, and as another poster stated, just get one from a store that has a lifetime warranty. Obviously, in your case, YMMV.

Reply to
Kruse

Well, you can cry BS based on your experience, but I've seen PLENTY of people complaining about them going bad on Mustangs alone. It's highly unusual for someone to mess with the idle screw on a newer FI Mustang. When these problems crop up, most times the problem is the IAC. I was talking about this very subject with a buddy that manages the performance parts counter of a sizeable Ford dealer and he said the IACs go bad on many Fords...not just Mustangs and not just 4.6s. The 4.0 SOHC in my Explorer is prone too. He sees a more sizeable sampling of problem cars so I tend to believe Ford has a problem with IACs. Glad to hear you've been exempt though. Hope your luck continues.

Reply to
Keith

The ones from Auto Zone is even worse.

Reply to
WindsorFox[SS]

Mike King wrote: > When the IAC is disconnected the engine

Whoa. Are you positive about that???

Reply to
WindsorFox[SS]

Yes, at least on an EEC-IV 5.0 unless they changed it after the '90 model year. I clearly remember this from back in the day... early 90's when I had my '89 GT. The IAC was failing, so I used the stop screw to up the idle and when I replaced the IAC the idle was surging. Per a non-Ford EEC-IV manual, I think it was How to tune and modify Ford EEC-IV, I set the stop screw to the proper gap and set the TPS below 1v and had a perfect idle again. The manual mentioned that when set correctly the computer controls the idle, and when the IAC is disconnected the idle will drop and the engine should lope to a stall in a few seconds. That book was the best EEC-IV guide available at the time.

Reply to
Mike King

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