Haha, again, sorry to make so many threads, but I've got a new problem! yay!

Alright, so I had a very high idle (3.5k rpms) so I replaced the IAC, as it was completely dead (pintle had zero movement)

Unfortunately, that did not completely solve the problem, only partially. Now when the car is out of gear, it idles in the high 2k, almost 3k rpm's, which is a drop, believe it or not haha. Unfortunately, when I put the car in gear, the engine stays revving high, around 1k RPM's, which makes the car pull, it's essentially like the gas pedal being pushed down.

I can hit about 30mph with my foot completely off the gas. Now, I'm no doctor, but medically speaking, that's bad haha. So, my next thought was TPS. Checked the voltage on it, and it reads 0 volts with the throttle closed, and only hits 3.5 volts at WOT. From some searching, I understand that the range should be .45 volts to 5 volts. Is that correct?

If that is correct, am I also correct in assuming the TPS is causing the problem or am I completely skipping over something? I've tried an ECM reset, car was recently tuned up (plugs/wires/filters/oil), and as I've said, the IAC is new.

Anyways, here's the video, I'd really appreciate it if you guys could help me out with this because I love driving my car, but it's just not safe to with it acting like this.

I'm sorry, I have no idea how to embed videos, so I'm just posting a youtube link:http://www.youtube.com/watch?v=3d-IT-XQ1vw

Yes, I have a funny voice

 

Replace the throttle position sensor. My uncle's mustang gt had the same, very same problem and we replaced the tps without anything else and it fixed the problem. his was idling at around 2-2.5 thousands, and it was not very drivable because of it running so rich, if replacing the tps does not fix the problem, check the ecu. something with the computer, if you have to follow the wire from the tps to the ecu and make sure it's all good. the tps is making your car run rich and only replacing it will fix your issue

 

Replaced the TPS.

No change.

Any other ideas?

 

Set the tps and iac correctly......tech article is on the main page. These need to be set together and in order. Does the throttle body close all the way to the bump stop. These older throttle bodys bushings wear out and sometimes wont allow it to close all the way. Clean throttle body as well.......pull it off and clean it good.

 

You mentioned you recently tuned it up. Was it doing that prior? Or did it just start the high idle all on its own one day?

Is the accelerator cable on the manual idle stop while its doing this?

My money would be on the TPS sensor not being set correctly, engine sounds really smooth in the vid!

 

Throttle body closes all the way, and is quite clean haha, I cleaned it in a parts washer when I got the car (I work at a dealership).

Just started doing it one day, cables/bushings are all good, and set according to a shop manual.

I'll try setting the TPS/IAC again, though I followed the tech article the first time

 

have you tried looking for a vacume leak, if not try spraying carb cleaner lightly in small sprits all over intake to heads,plenum runners,throttle body. and hoses

 

No vacuum leaks, that was actually one of the first few things I checked, because it does sound like a bad leak problem.

Well, I backed out the idle screw pretty much all the way so that the throttle rests on it's back stop, rather than the screw haha. That's the only way I could get it anywhere close a normal idle, currently at 900 rpm out of gear, about 500 in gear.

 

I rigged a spring on mine because my throttle body is worn out and caused a high idle. Works just fine untill I get the funds for a new TB. Ran the screw out untill in touched the blades at the rpm I wanted, then put a spring on it with enough tension to keep it back on it........works fine and pedal feels just fine with the spring.

 

Unfortunately mine is alllll the way back at the TB's bump stop, not even the screw haha, and it's still idling high.

This is making me crazy, I know it's going to be something stupidly simple, too.

If it makes any difference, I'm now getting bogging. Say I'm at 20mph, if I hit more than about 50% throttle, it's pretty much choking, until it finally catches up, which almost sounds like a spark problem, but I checked for spark after it happened, and I'm getting good spark on all cylinders, no cracks in my distro cap, so no chance of water seeping in.

 

Try unplugging the MAF and see how it runs.

 

did you check the electrical connections to the tps?? My uncle's mustang is a 5-speed, and his has the 5.0 HO. it had been sitting for about 4 years and he needed it back so he brought it to my house where me and a good friend of mine worked on it, when it finally got started it ran really really rich. it was idling out of gear at around 2000. we tried many things to get it running right and ended up pulling off the tps and it ran correctly. so we knew what it was, and we replaced it. started it up again with the new tps and it idled back down at about 800. from what you said and from what I saw in the video it was the same problem

 

possibly coolant temp sensor, but i'm leaning on the tps as well.

what would seriously help you is getting an aldl cable.. that way you can see what all the sensors are reading so you can determine which one is out of range (if cts reads -40 or the tps says you are at half throttle, etc).

 

TPS was replaced, no change. CTS was replaced, no change.

Haha, jeeze this is terrible. I guess all that's left is to check the MAF. Again. Because it was fine when the problem started, but who knows.

 

what did you do to the car right before all of these problems?

 

Your car doesn't even have a MAF, 91 is speed density so im not quite sure what you checked before. Are you sure you don't have a big vacuum leak that is the most likely cause. On a 91 the TPS is not adjustable so as long as it's showing around 0.5-0.6 volts with the throttle closed that is OK.

 

Wow, brainfart on my part, I meant the MAP.

And I didn't do anything to the car before this started. I had a high idle randomly one day, so I replaced the IAC.

 

This sounds like the PCV is stuck open (or removed) allowing air to come from the crankcase and enter directly behind the throttle body.
One hose goes from in front of the throttle blades on the TB (in through the air cleaner) and goes into the crankcase. The other hose removes crankcase fumes/air and puts it into the intake (but restricted by the PCV valve). Be sure you have them connected correctly and the valve is moving. The one that comes from the PCV goes directly to the plenum at the TB and would cause this to happen like the throttle is open.
HTH

 

The pcv rattles when I shake it, which is how I've always tested them.

 

you said the throttle body closes completely right?
well if it does then why don't you check the injectors because it'll run rich even when the throttle body's closed if there's something wrong with the MAP, or the TPS. I leant towards the TPS because I've seen a problem like this before, but you said you changed it out. Is EVERYTHING on the car in working condition? I mean, everything everything also because if everything's fine then the only problems would be something to do with fuel delivery. so I beleive you should make sure that everything even not involved with this problem is good. then you can focus on this problem only

 

Perhaps you could explain how you think bad fuel injectors could cause a high idle??? Fuel delivery problems in no way are gonna cause a high idle condition. If you have the throttle body completely backed off the idle screw stop and it's still idling at 900rpm then you have to ask yourself where is the engine getting the air to run from? If it's coming solely from the IAC valve you should hear a loud sucking noise from around the throttle body area. You can verify this by removing the intake boot thing from around the throttle body and you will feel and hear where it's sucking air from. If that's the case then your IAC is bypassing too much air for some reason and you need to go from there and fix it. However I suspect you have a vacume leak somewhere else that is causing the problem (the PCV was a good sugestion) easy to eliminate that as a possibility just unplug it and plug the hose. If there is a big vacume leak the computer is gonna try and meet it's target idle speed by closing the IAC and hence you wouldnt hear the air bypassing at the throttle body it will be pretty quiet. I would try and diagnose it by first forcing the IAC to close (there is a way to do it by shorting 2 pins on the ALDL connector) and then unplugging the IAC if, With the idle screw completely backed off it still idles high then you deffinately have a vacume leak somewhere.

 

I agree it sounds like a vacuum leak, but I can't seem to find one haha. The IAC is brand new, literally less than 100 miles on it.

 

bad injectors that are too big will allow excess fuel to enter the engine. my uncle's 88 mustang had a bad tps, it was idling very high at around 1500-2000 rpm, and it wouldn't die down. we checked to make sure that the throtle body closed completely and it did but it still had a very high idle. we experimented with several things and finally just took off the tps and it ran fine. so we bought another one. with the new one on it ran just like new and it had the idle back to about 700. The reason for the high idle was that the computer was getting the reading of open for the tb even though the tb was closed. so the computer fed extra gas to the injectors and engine and it idled high. his is a standard though and he didn't want to drive it like that so he didn't while we fixed it

 

Well where should I begin? A Mustang is made by Ford, Camaro's are made by GM they have absolutely nothing to do with each other apart from the basic configuration of the car! As for putting more fuel in the engine because of misssized/faulty injectors adding more fuel without also adding more air will not increase the speed of the engine if anything it will cause the engine to load up and slow down! Pull a vacume line off a running engine what happens? It speeds up, Open the throttle on your engine and what are you doing, adding air and the engine speeds up.dumping in more fuel does not in itself cause the engine to accelerate. A bad TPS might cause idle problems but it would be because the computer doesnt know whether it's supposed to be in idle mode, AE mode, PEmode, DEmode, whatever, and it might be advancing the timing or opening/closing the IAC, all kinds of possibility's. Incidentally tchernobog have you checked your timing through all of this? If it's way off it could cause problems.

 

I don't wanna get into an argument, but how would you explain the closed tb but a high idle then?? and the problem being solved by replacing the throtle position sensor??

 

He allready said it......."vac leak". Dont matter if the throttle body is closed if its getting air somewhere else its gona compensate by raising the rpms. You cant always find a leak with a bottle of carb cleaner or the human ear. Put a smoke machine on this car and rule that out for GOOD! Check throttle body gaskets, check the small vac port under the throttle body, CHECK THE INTAKE GASKETS!

 

I already explained that in the previous post A faulty TPS signal will cause the computer to do strange things based on what position it "thinks" the throttle is in, It could be advancing the timing, which causes the idle to go up or it could be opening the IAC which will also cause the idle to increase. I'm not trying to start an argument either but before you start giving advice you might wanna get a better understanding of basic engine fundamentals and more specifically TPI engine fundamentals being as thats the board we are in now.

 

Have you checked your brake booster to see if it holds vacuum?

 

well that's kinda what I'm trying to say, you just had better words for it. I'm not the best explainer but i know what I've done with problems on several cars before, and the vacum leak theory seems very plausible just it's very hard to find it, or it doesn't exist, which could lead to be the explination that you said the computer is advancing the timing for some reason or there's a faulty tps reading. which is why I recomended earlier in the post to check everything on the tps. but you might be right also, this sounds really out there though

 

If the TPS is reading reletivly close than it shouldn't be the problem. You're going to need additional air to get the RPM up like that.

Try doing the IAC reset again but leave the connector off once it is fully extended (closed) by jumping the A & B pins in the ALDL connector.
The IAC would be disabled basically and not let any air in.
If you still get 3K idle, remove the new IAC and see if it appears extended.
Maybe the one you got as a replacement is not operating and is fully open.
Its a long shot but if you have no vac leaks elswhere from PVC, Brake booster, Manifolds, then there are only a few possible places that much air can get in. Confirmed each by disconnecting from the plenum or TB until you find the offending device.

Check the canister purge line that goes to the TB.
I ststed the PCV goes there but that's just how I replumbed mine.
The stock setup has PCV into the underside of the plenum, Canister goes to the port behind the throttle blades on the TB.
That would be my #1 suspect.
https://www.thirdgen.org/forums/atta...m-diagrams.gif

 

I'll try another reset of the IAC, I suppose it's always possible that it was just faulty. Ran it on a smoke machine today, could not find any vacuum leaks haha.

I think I have gremlins

 

When you set your iac and tps, does the throttle body stay slightly open........as in you actually have to push it back to get it to sit on the idle screw. Are you absolutly sure the pintle has good contact in the throttle body??? If there is any carbon in front of that pintle in there it needs to be cleaned better........I mean metal to metal.....

 

No, it doesn't rest slightly open. Throttle body was removed and run through a parts washer and then cleaned by hand with carb cleaner.

 

So what is it actually idleing at out of gear as of right now???

If you trully have everything set dead on and there is absolutly no vac leaks, the only other thing I can think of is the ecm or bad wiring to the sensers. Can you here the iac motor running when you turn the key on without the engine running? You should be able to here the pintle extend for a few seconds when ya first turn the key.

 

It currently idles at about 1k out of gear, 5-600 in gear.

The pintle moves fine.

I'm pretty much at the point where I'm going to say screw it. 600 in gear isn't that off, and it's certainly better than the 2k it was at. It bothers me, but I have no idea what else to check.

 

I know i've just been sayin replace the tps, so I'm not going to recomend that again, but I would suggest taking your manifold to have it fogged to check for a vacum leak, and if not just replace all the seals, maybe that might help no??

 

read back, he allready fogged it brother.

 

This is what I have learned.
I know that the throttle blade must be opened a fixed amount for baseline idle with the IAC valve completely closed and no ECM timing control.
Any need to increase/decrease the idle in closed loop is done by controlling bypass air any change not requested by the ECM should be considered a leak.
I myself have found that I must obtain a steady idle at the specified rpm when performing the minimum air rate procedure before I can properly troubleshoot an idle issue. My reasoning for this is that at a fix air rate and timing advance the blade opening should be very close to spec if it needs to be completely closed then unmetered air is entering the air intake system. You could say that if it idles steady when setting the baseline then there shouldn't be an idle issue, true, but some leaks may only be apparent when the air pressure decreases (vacuum increase.)

 

Maybe try soldering on a new TPS connector? I have found several of these old brittle connectors on my car that weren't any good.

(FWIW, 'TPI Parts' has pretty good connectors)

 

oops, sorry. yeah well 80schild's theory sounds plausible, no?

 

Bought a new pigtail when I replaced the TPS. Yea, I've definitely learned through a lot of headaches and this being my third 3rd gen that the connectors are bad quite often haha.