So i've been working on my van to fix the high idle. I checked all my vacuum lines and the only one that was messed up was the line running from the Vapor Canister to the vapor canister purge valve. I have replaced that and it is no longer an issue.

However this is what i am experiencing.

If I unplug just the IAC valve the car idles great.

If I unplug just the vacuum hose from the MAP sensor the car idles great, except with a vacuum leak

If I unplug the MAP sensor wiring, the car idles great but i get a Check Engine light.

If I have both the IAC and the MAP sensor plugged in it idles through the roof.

I'm thinking its a bad MAP sensor. The IAC appears to be actuating properly as just pulling the vacuum hose from the MAP does not cause a Check engine light and the idle comes down.


Thoughts?

 

I've been doing some reading, and I guess one other thing could cause the issue would be a bad TPS.

 

You didn't mention Year, engine that your working with.

Here's a Link to checking sensors on all engines.

Generally, a high idle would be caused by a vacuum leak.

Do you have any way to pull codes??

 

Sorry it's a 93 5.8.

And it wasn't the map. Still troubleshooting I've followed every vacuum line from front to back and they are all good. Even shot starting fluid ar every vacuum connection as well.

 

Kewl.........that my era / engine

Check the lower intake manifold, at the rear of the engine *dog house removed* Spray some starting fluid around the corners where they meet the heads, known weak spot for the intake manifold.

Also.......this is a 22/23 year old engine, the rubber vacuum lines can become dry rotted, and replacing all old lines is a good solution. Also check all the hard plastic vacuum lines, one could be cracked/broken, and sucking in additional air. At worst, the TB gasket, upper (plenum) gasket could be leaking.

The problem with this era engine, is you can not get the codes to read direct to just an vacuum leak. And......then there is the EGR valve problems. Try to check the EGR tube, that's behind the alternator to see if it cracked/rotted out. A dirty EGR valve can cause a high idle also.

And, if you really what to get into this........This Link will give you all the sensors to check and test

 

Thanks for all the suggestions! I'm new to these model engines. Its the first of the old model ford V8's that i've owned. The old engines i'm used to are the ford 2.3l Turbo engines. I skipped right over the SBF engines straight to a Coyote v8 on my 2012 GT

It got late today and I had to stop, but I definitely narrowed it down to NOT the MAP and NOT the IAC valve. I'm about 90% sure its the TPS because i noticed that if I floor the throttle and let off fast that the idle comes down to a normal range and idles along perfect, but if i even graze the throttle after that it goes right back up to high idle until it floor it and let off fast again. I think the sweep of the TPS is totally jacked.

I'm going to start with the TPS test from your link the next time i get a chance to work on it.

While i was messing with it i was spraying starting fluid at every nook and crack that could possibly get sucked into the engine on the back and nothing made any difference so i think all the gaskets are still good. What are the "EGR valve problems" you speak of?

 

Just to let you know, the TPS ended up being the problem. Once I replaced it everything is running great now!