Throttle Position Sensor and High Idle Issue

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uxler

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Just bought a 93 Mark VIII and the cars been idling between 1200 and 1600 rpm. So I bought a code reader to determine the issue and it read 12 (system cannot raise engine speed above normal idle) and 63 (throttle position sensor signal voltage is too low). Next, I pulled the throttle body, cleaned it thouroughly, bought a new TPS and installed that, and replaced the obviously worn throttle body gasket with a new one. I reassembled everything and put it back in place.
I started the car again and its now idling at 3000+ rpm. What should i do next? Does the computer need time to adjust to the new TPS having possibly compensated for the bad one? Do i need to adjust the throttle screw position or the TPS position? Any ideas?
 
I would check the voltage the TPS is putting out i think its the green wire key on test. Should read below 1 volt(i like .96V) at idle then as you open throttle should go to 4.8V smoothly no crazy jumps. Also you should of replaced the IAC while you had it apart,there cheap. IAC is Idle Air Control so that is what controls your idle, these gum up alot. Frank
 
I was gonna say Idle air control.


You may even have a vacumn leak. Check your vacumn lines, with a 3000 idle, it will prolly be a big one. (if it is even that, just an idea.) Think brake booster


Mike
 
I agree with above mentions. Idle Air control valve or vacuum leak. But the IAC is more likely cause generally a vacuum leak big enough to cause 3k RPM would be sufficient to stall the engine.

I would also check the throttle cables and make sure there is smooth operation of those.

How did you clean the TB? Did you use the correct cleaner? Using the wrong one can result in issues, carb cleaner is the worst. There is even a label on the TB indicating not to clean it. If you remove the coating the TB can freeze up :( and gum up a lot faster.
 
I removed the throttle body to replace the TPS and cleaned it with throttle body cleaner. Lubed it with CRC and checked the cables for smooth operation. Replaced the throttle body, re- connected the hoses ect., started the engine and it was at 3,000 rpm from the start. I restarted the engine 4 or 5 times and each time it went straight to 3,000 rpm and stayed there until I shut it off. Disconnected the battery for an hour or 2, re-checked the codes and I got the same 12 and 63.
I did not replace the Idle air controller, allthough I wanted to. I could not figure out how to get it off without removing the intake maifold.

Can I disconnect the TPS and still start the engine? It may help to eliminate it as the source of the problem. Same for the Idle Air Controller?

Is there a specific setting for the idle adjustment/throttle stop screw? I can't get at it to adjust it while it is on the car. I was thinking that it should have a setting in inches or MM for the distance of the screw.

I really love the car and other than the idle issue it runs great. I drove it from Boston to Baltimore on the day I bought it and did not find any other issues.
Can someone reccomend the best manual to buy for the MARK VII? I was looking at some of the CD type manuals on ebay, but not sure if they are any good.


Desparate
 
NEVER touch that screw. It a a screw type screw, if you screw it your screwed!

But it sound like you did everything by the book! Great! You can try tapping the IAC, that usually makes it snap into place, or try disconnecting the wiring harness to it. Both can work.

The IAC can easily be replaced if you have small hands and a couple u-joints and extensions to work with. It is a lot easier with manifold removed, but that opens a can or worms. Deep sockets will be needed for one of the bolts/nuts. You basically go in from behind. Removing the windshield wiper cowl may help and is certainly easier then taking the manifold off!

Nothing beats the real thing, but the CDs have been great if you have a PeeCee. You can search and stuff fast, in many ways its better.
 
Oops... TPS, yes you can take it off, but I doubt if thats the problem. A new sensor would most likely not be faulty. Unless installed wrong? But I think thats pretty hard to do. On the TB one plate at idle should be close, the other a little open at one that plate reaches 25 degrees, the other starts to open.
 
And I just realized, must be the IAC. Because at 3k your throttle plate would HAVE to be open. At 3k the AIC would be closed? right? There is no way the engine is running at 3k unless it is getting some serious air which a TB at rest could not pull.

I still dont like the three 3k RPM though, that is really high, even for the AIC being bad.
 
Went ahead and bought the IAC on everyones advice and it dropped the idle back down to a little over 1K in park and 900 in drive with foot on brake. Looks like mine was bad, so thanks for the help. Any suggesstions on how to drop the idle from here. I can live with it where it is but id like to get it where it should be around 6-700. Also, when hitting the gas pedal the engine is slow to return to idle. It hangs for 2 or 3 seconds and then falls slowly back to idle.
Almost there.
 
How dies it "feel". Could the tach be off a it? Does it drop all the way down when off? Just checking :) If you get a chance, pull the intake tube (again) and make note of the positions of the TB plates, unless you already have. Make sure one is closed and the other is partially open, just a bit. Car does not have to be one. I just want to rule out a cable problem, they are not exactly resistant to failure. FYI - You can not get a new one anymore :(

Otherwise start checking for vacuum leaks with a carefully sprayed amount of starting fluid or something similar. There is also a T fitting that attaches near the TB for vacuum, VERY common leaker!
 
Tach feels accurate. Both TB plates appeared to be closed. If it was open it couldnt have been much at all. Throttle cable seems to operate smoothly. Going to replace a few vacuum lines tommorow, ill let you know how it helps. On a different note, tommorow im also going to attempt to replace the speedo gear at the transmission. My speedo sticks and is jumpy so im guessing the gear is worn. If anyone knows about this issue please chime in. Thanks again for the help guys.
 
I just got to thinking.....


are you running the car with the intake tube off of it? If so, your not allowing the MAF to do it's thing which WILL cause the engine to run funky.


Just a thought.


Mike
 
try reseting the computer again, start it and let it idle in park for five min, then drive it for about10-15 min at speeds over 35. its worth a shot, the computer could still be trying to re-learn the idle strategy
 
Has anyone ever tried this method for checking for a vacum leak?

Take a propane torch and turn it on but do not light it. With gas coming out run the torch over all the vacum lines and listen for the enginge to rev up slightly. The spot where the torch is when the engie revs up is where your leak is.

I've only heard of this. I'm just wondering if there is any truth to it or if it works at all?
 
Thanks,
I'll try to re-set the ECU again and drive it.

No, I never heard of the propane test, but it sounds like it would work.

Happy New Year
 
Its something I heard from an older guy from the days of carbs and manual chokes. With all the elctrronics it seams like you have to be a lot more careful with everything.
 
It's Fixed!!!!!

Thanks to all, for the prompt replies, ideas and direction. The problem is officially fixed!!!!
The TPS and IAC(see note **) were replaced. Tried to clear the codes out with a code reader, but ended up diconnecting the battery overnight before the ECU was reset. After the overnight reset the car runs like new!

** For the IAC I used a 5/16" Craftsmen ignition wrench (very small with a slight off-set) to break the nuts loose. Then I pushed a 10" piece of vacuum hose onto the end of the bolt and twited the hose to back out the bolts. Replaced the bolts with the hose and tightened them down the last turn with the wrench.

Thanks Again
 
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