Help with High Idle on 91 T-Bird Pleaseeeeeee

Hey Folks, need some suggestions. 91 T-bird. 5.0 V8. Kids car. The problem is high idle. In park , it will start out at 1200 rpm cold and as it warms up it reaches 2000 rpm. In drive, the rpm's is about
1200. I took the throttle body apart and found the opening to the egr valve plugged solid. I thought this was the problem. I cleaned everything real good. Didn't make a difference. I checked for a vacum leak using wd-40 and holding a 2' hose to my ear to listen for one. I found one small hose that came off, but didn't make any difference. I cleaned the mass airflow sensor. and looked at what I believe were the Throttle position sensor and the idle air soleniod. There is No engine trouble light on either. Don't know how to get error codes or how to test these devices. I had the idle air soleniod replaced about a year in a half ago. With the engine running , if I unplug the TPS or the idle air soleniod , there is no difference in the engine. If I unplug the mass airflow sensor the engine stalls out. (before this problem, I replaced that steel mesh filter under the pvc valve that appeared plug. I was getting a lot of oil getting in to my air filter.) I know its hard to dignose something like this in a forum. If anyone got any suggestions or things that I can check I would greatly appreciate it. I'm at the point now that I will have to take it into the shop if I don't figure it out with help from this forum. You know how expensive that can be. Thanks!!
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I have a similar problem on my 1990 Escort GT, following the calibration procedure for my car, I can't get the idle below 1200.
Try plugging all of the vacuum ports on the intake. These are normally the EGR tap, PCV tap and manifold accessory vacuum tap. I tried this on my car and there was no difference in idle speed. At least now I think I can rule out the vacuum/pcv as sources of unmetered air in my case.
Moving on, the next area of speculation would be the throttle body, intake manifold or crankcase. I think with the speed density systems (MAF or vane air meter) the crankcase must be sealed, but I forget why. Probably because air can get into the combustion chamber through that route. I was reading this somewhere following a google search on VACUTEC. This a brand of smoke tester that is used to pressurise an intake/engine with harmless smoke to determine where leaks can be found. I haven't found a shop that has this tool yet, but you can get one for about $1000. <g>
I tried the propane method with no results. I even have a schrader valve from an old bicycle tube fixed to a 1/4" rubber hose I can connect to the accessory vacuum manifold, but without a vacuum regulator to limit my air compressor to 3 lbs. or less I'm not about to hook it up to the engine.
Writing this, I came up with another idea, restricting the crankcase ventilation tube. I'll let you know if anything happens.
Matt
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It may still be the IAC valve or the TPS. These cars are actually pretty easy to diagnose, but you need a way to read the engine codes. Invest in a digital code reader for about $35, and you'll be able to figure out pretty much anything that's wrong with the engine controls, and some brake problems also. See: http://www.dalidesign.com/hbook/eectest.html
mudbone wrote:

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mudbone opined in

Killing with MAF disconnected says there's another sensor problem. If engine starts and runs fair with MAF disc, then that USUALLY means the others are in spec.
Replace the TPS... Cant miss it, it's the black plastic thing on the throttle plate shaft.
If it's adjustable ( arced slots instead of screw holes), you're going to have to borrow a DVM ( ~ 0.97 volt KOEO)
DO NOT adjust throttle stop. If you have done so, you will have to adjust it first (500-550 rpm - IAC connector disconnected) and eliminate possible vac leaks before that.
--
- Yes, I'm a crusty old geezer curmudgeon.. deal with it! -

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Found the problem! Thanks to a thread I found in this forum thats almost a year old. It was my Idle air control valve (IAC). I did exactly what Dan said he did.( in that previous thread.) I made a restricter plate out of plastic. (used the side of a plastic bottle and basically cutout the pattern of the gasket.) On the bellows side a put a 1/4 inch hole. the other side I left fully opened. Now I got 800 rpm's in park and 1000 rpm's in drive. I wonder if this will last a while. I just had this part changed about 18 months ago. The car is rusting out and I don't want to put any more money into than I have to. thanks again for all the replies!!!
Sun, 06 Feb 2005 16:54:21 GMT, Backyard Mechanic

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