Very High Idle

[Fernando87mj]

well this morning I went and started up the jeep and when it started it started idling like crazy the rpm's went to about 2500 rpm so immediately shut it off :???: . do you guys have any suggestions on what it could be, I don't have a lot money either to be replacing a lot parts too .  :dunno: :dunno:

[AeroNautical]

Alot of good information in this post, shares the same title: http://comancheclub.com/topic/38612-very-high-idle/

 

I had that problem recently, my TPS went bad and would occasionally send the wrong voltage, giving the engine alot more fuel than it needed, causing a high idle, especially on start up. If you have a manual transmission, you can use an auto TPS, but not vice versa. Auto TPS' are a hell of alot cheaper anyway, about $35 on rockauto. 

[jeepsouth]

My idle has increased some with the cooler weather ,or so it seems. Has anybody else had this happen?

[Fernando87mj]

alright thanks for the info , so I went and disconnected the tps and started the jeep up and it idled perfectly so I went for a drive and it all went good, the only thing I noticed was that the shift light won't illuminate anymore is their any problem driving it with the tps disconnected, in the meantime until I get new one :hmm: :???: :???:

[onlyinajeep726]

Manifold bolts may need tightening.  I know that sounds crazy, but check this out: http://www.fourwheeler.com/how-to/154-1005-jeep-cherokee-xj-problems-and-fixes/

 

 

Run, Run, Rudolph
Maybe it is age, maybe it is mileage, but we've seen a lot of Renix-era ('87-'90) Cherokees where the bolts holding the intake and exhaust manifold to the six-cylinder engine work themselves loose and cause the engine to race around 2,000 rpm.

Prevention: Tighten the bolts, dummy!

Cure: Tighten the bolts, dummy!
Seriously though, if your Jeep isn't doing this yet, just check the bolts. If it is idling erratically, grab your 9/16-inch wrench, get the Jeep to operating temperature and tighten the bolts while the Jeep is hot. Be wary of over tightening, though-they like to snap. If you let the leak go for too long you might need to just bite the bullet and put in a new gasket, but often tightening is all that is needed.

[AeroNautical]

Wait a minute, you could drive it without your TPS connected? I didn't even think it could start without it. I would not recommend it, because that's the only thing that tells the ECU how much fuel to give the engine in relation to how open the butterfly valve is. I think what was happening was your engine was getting a constant, steady flow of fuel, but when you used your accelerator pedal, it only introduced more air, allowing a better combustion. Did you notice a huge drop in HP with it d/c?

[onlyinajeep726]

Yes, it will start and run without the TPS, but like PFC said, it's not recommended and the ECU needs to know the position of the throttle for optimum performance and MPG.  Otherwise, it has to rely on the O₂ sensor and MAP sensor to sort everything out... 

[Fernando87mj]

yea It does starts and drives just fine but yea your right It didnt feel like how it normally does hopefully I can find a good tps at the junkyard later

[Rockfrog]

My 88 has idle issues ... occasionaly starts with a high idle, sometimes as high as 3000rpm but usually around 2500.

When it happens I just turn it off, restart, turn off restart until it idles fine again. Usually goes back to normal after three starts. I have a new IAC and will eventually replacebthe tps but it's not a major problem for me at the moment. I'll deal woth it when I tackle the wiring and head swap (HO head, intake, and exhaust).

[cruiser54]

When dealing with TPS issues on a Renix, always do a sensor ground test first.

 

Cruiser’s Renix Sensor Ground Test

This sensor ground circuit affects the CTS, TPS, IAT, MAP, ECU and diagnostic connector grounds. It’s very important and not something to overlook in diagnosing your Renix Jeep as it is common for the harnesses to have poor crimps causing poor grounds. If any or all of the sensors do not have a good ground, the signal the ECU receives from these sensors is inaccurate.

Set your meter to measure Ohms. Be sure the key is in the OFF position.  Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector of the TPS . The letters are embossed on the connector itself.
Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it runs parallel to the valve cover and also near the MAP sensor mounted on the firewall. If you have an 87 or 88 with the C101 connector mounted on the firewall above the brake booster, wiggle it, too.

You want to see as close to 0 ohms of resistance as possible. And when wiggling the harnesses/connectors the resistance value should stay low. If there is a variance in the values when wiggling the wires, you have a poor crimp/connection in the wiring harness or a poor ground at the engine dipstick tube stud. On 87 and 88 models, you could have a poor connection at the C101 connector as well.

Revised 06/12/2012
 

[cruiser54]

And, if it's an 87 or 88, do the C101 connector refreshing.

 

Renix Jeep C101 Connector Refreshing

The C101 connector on 1987 and 1988 Renix Jeeps was a source of electrical resistance when the vehicles were new. So much so that the factory eliminated this connector in the 1989 and 1990 models. The factory recommended cleaning this connector to insure the proper voltage and ground signals between the ECU and the fuel injection sensors. We can only imagine how this connector has become a larger source of voltage loss and increased resistance over a period of almost 25 years. The C101 connector needs to be cleaned at least once in the lifetime of your vehicle. Chances are it’s never been done before.

Almost every critical signal between the engine sensors, injectors, ECU, and some to the TCU, travel this path through the C101 connector.

The C101 connector is located on the driver’s side firewall above and behind the brake booster. It is held together with a single bolt in it’s center. To get the connectors apart, simply remove the  ¼” bolt and pull the halves apart. You will find the connector is packed with a black tar like substance which has hardened over time.
Take a pocket screwdriver or the like and scrape out all the tar crap you can. Follow up by spraying out both connector halves with brake cleaner and then swabbing out the remainder of the tar. Repeat this procedure until the tar is totally removed. This may require 3 or more repetitions. Wipe out the connectors after spraying with a soft cloth.

If you have a small pick or dental tool, tweak the female connectors on the one side so they grab the pins on the opposite side a bit tighter before bolting both halves back together.

Revised 03-02-2013
 

[Fernando87mj]

cleaned the grounds and still high idle :doh: :doh:  ,do you guys think the napa tps or the oreily tps are any good :???:

[cruiser54]

Have you cleaned the C101 and done the sensor ground test? 

 

Napa TPS is okay. But, remember you need to adjust it using the instructions for the flat 3 wire connector. 

[Fernando87mj]

do you think that cleaning the throttle body might of messed it up , I cleaned the throttle body 2 weeks ago and it was running perfectly until yesterday .

[cruiser54]

do you think that cleaning the throttle body might of messed it up , I cleaned the throttle body 2 weeks ago and it was running perfectly until yesterday .

Nah. Do the stuff suggested. You have a meter, right? You're gonna need one to adjust a new TPS if it gets to that.

[Fernando87mj]

turns out it was the tps , I put a new one from bwd and started it up and high idle gone :thumbsup: :thumbsup: . thanks for your support guys :thumbsup: