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Old 08-07-2011, 11:36 AM   #1
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97 TJ Throttle Position Sensor failure?

I own a 1997 Jeep Wrangler 2.5l and yesterday while driving home I shifted and noticed that the throttle had begun idling at approx. 2200 rpm's (normal 800) I went to pull over and the brake pedal was stiff as a board. (recently had a brake overhaul and have had no issues since/nothing i can notice that would cause that so im assuming its related with the throttle issue) Upon stopping i immediately noticed under the hood that the throttle return spring had snapped. I got the vehicle home safely and today bought a universal return spring. I noticed in some pictures and statements online that there should be a small hole for the anchor point of the spring but it appears my jeep does not have one, i was able to anchor the spring how i recalled it being previously positioned. However, when i started the jeep i still had the high throttle issue. Any information on how to troubleshoot and fix this? My next guess would be the throttle position sensor, but i'd like to know if there is a way to find out exactly what the cause is without systematically replacing parts. Still a bit confused as to why this throttle issue would cause the brakes to act the way they are.

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Old 08-07-2011, 02:12 PM   #2
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That your brakes are stiff and you have a high idle indicates, likely, a vacuum leak. Check that the large diameter (3/4" or so) vacuum hose that connects the power brake booster to the intake manifold is connected and leak free.

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Old 08-08-2011, 05:53 PM   #3
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Jerry, you got me pointed in the right direction, perhaps you can help me a little bit more. I do recall upon getting out of the vehicle following the initial issue there was a good bit of fluid on my drivers side short fender flare that had a minute drip residue line from the jeep emblem but not from the engine bay or anywhere up higher which puzzled me enough to not factor it into the equation. I just took it for a test drive and the brake pedal is not completely stiff and i have "some" braking power, however while driving i did notice while accelerating a whistling coming from what i interpreted to be near the intake manifold. (i do not have anyone around to help me currently) Upon reading your advice i checked all vacuum lines and noticed (as in the picture) the line running from the throttle body, to the top of the engine had some oil on the outside of the insulation. upon pulling the insulation off i noticed on the end where it goes into the throttle body. fluid covering the line however i could not discern a place for it to be leaking from, the fluid only covered from the throttle body to about the halfway point of the line. The connector into the throttle body didn't seem to be loose and did not appear to be gurgling fluid or etc. Could this in fact be the issue, and if so do i need to simply replace it? (in the past few weeks i have done a number of things to get the jeep back in tip ship including brake overhaul with new hubs by a mechanic, while at mechanic they didn't place my power steering fluid tank back properly on the mount and it bounced off into my fan which i had to replace, replaced with electric fan, following that i put in new spark plugs and wires and cleaned the distributor cap, added a some injector cleaner, i realize i most likely dont need to tell you all this but all of this was all done within a 2 week period prior to this issue so i assume it couldnt hurt.) I realize i lost track and rambled on a bit so if theres any piece of info i left out just let me know
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Old 08-08-2011, 08:10 PM   #4
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The vacuum hose I am talking about is the one that connects to the power brake booster on the driver's side firewall. It is perhaps 3/4" in diameter and is what provides vacuum from the intake manifold to the power brake booster. Vacuum is what powers the power brake booster... that big black round thing 8" or so in diameter bolted to the driver's side firewall behind the master brake cylinder.

Neither of your two pics show it or the hose.
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Old 08-08-2011, 08:39 PM   #5
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i see the hose, too dark to really look or take a picture but its not hooked to anything. noticed it earlier but didn't see anything for it to plug into. thats definitely the problem then and im sure i can find its place in the morning. thanks much
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Old 08-28-2012, 02:48 PM   #6
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Quote:
Originally Posted by Jerry Bransford View Post
That your brakes are stiff and you have a high idle indicates, likely, a vacuum leak. Check that the large diameter (3/4" or so) vacuum hose that connects the power brake booster to the intake manifold is connected and leak free.

I'm having the same problem however, while I was limping home I (was not sure why the idle jumped) while driving I lost all power assist on the breaks, and the idle went from being about 2200 to staying at redline, I have checked the vacuum system and thus far have not found any leaks, I was wondering if you might have any other thoughts on what might cause this problem? Any suggestions are appreciated, and thank you in advance.
PTB
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Old 08-28-2012, 03:10 PM   #7
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Losing the power brake assist AND experiencing a high idle rpm is a clear sign of a vacuum leak somewhere. The power brake booster is vacuum powered so for example, if the vacuum hose between the power brake booster and intake manifold was to come off or develop a leak in it, you'd both lose your power brake system and have high engine rpms.
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Old 08-28-2012, 03:19 PM   #8
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Guys I have no clue if this will cause ur brakes to get stiff, or rev your engine high, but there is a vac line that goes to the heater control switchs that was under my battery, when I removed the battery to install a new blower fan I found the almost worn threw vac line

Dunno if all jeeps vac line is routed under the battery but it wouldn't hurt to check


Best of luck

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