I've never had this issue but from what i've read on this and other forum's i think your suspicions about the TPS could be correct. I've seen threads that describe removing the TPS and cleaning it up which may help you out. Sorry i can't provide more insight than this but that's where i'd start if it were me.

 

Do a search for cleaning the IAC. When it gets dirty, the engine idles weird, and sometimes stalls. It costs about 5 bucks in cleaner and 30 min of your time.

 

mines doing the same kinda. it idles low around 500 or so & some times when stopping or if im in 1st then back to neutral it drops around 250. I cleaned the TB/sensors very well & replaced the IAC with no difference.

 

Check for vacuum leaks. Spray some WD40 along your vacuum lines, brake booster, etc. If your engine idles up, then you have a vacuum leak there.

 

wont a vacuum leak cause it to idle high ? & I don't have any VAC leaks, I put clamps on the only two lines. its getting worse. it doesn't die, but almost every time I let off the clutch it drops to around 200 rpm the goes back to 500. it wont idle @ 750 anymore, idles @ 500 all day long.

 

Might be your throttle body. Happened to my Ford truck, when I would stop it would idle real low then die

 

what do you mean (explain please) ? like its warped or something ?

thanks

 

A vacuum leak will cause an extra high idle rpm, that is not your problem. What is likely causing this issue is a part of the throttle body called the IAC (idle air controller). The IAC is what provides all (!) of the engine's air after you take your foot off of the accelerator pedal. If the engine idles ok with a little gas but doesn't idle when you lift your foot off the accelerator pedal, it's assuredly a problem with the IAC. 99.99% of the time, any problem with the IAC is strictly that it is dirty... dirty enough that it isn't letting enough air into the throttle body at idle rpms, causing a low idle or stalling.

Take a look at the below illustration and take note of the slot (idle air control passage inlet) inside the throttle body in front of the Idle Air Controller. Using an aerosol can of throttle body cleaner, start the engine and while holding the butterfly valve open with the throttle linkage, aim the spray of the cleaner at that slot and maybe you can clean it enough so the problem goes away.

Better yet, get a torx-head adapter and remove the two torx-head screws that hold the IAC to the throttle body and remove the IAC. Then, using a toothbrush, rag, and throttle body cleaner, clean the solenoid actuated shaft coming out of the IAC of all the black gunk. Clean the hole in the TB it fits into too. Be GENTLE with the shaft, don't push/pull/twist it. It's not so delicate it can't be cleaned, but just be gentle with it.

Make sure to be careful removing the screws. They are held by Locktite so they will be tight. Use firm pressure to hold the torx adapter squarely into the screw head so it can't strip out the bolt head's torx opening.

 

welp, there's your explanation haha..

 

thanks jerry, but I replaced the IAC about 2 weeks ago, so its not that. I still have the OEM unit I thought was bad, but wasn't. it does this with both units. anything else that might cause this ? also I've recently removed the entire TB, took it all apart & cleaned it with a tooth brush including the surrounding sensors. it still looks brand new.

 

About the only other thing I can think of that can cause idle problems is the Throttle Position Sensor mounted 90 degrees to the IAC. It's nothing more than a big variable resistor that report the throttle position to the computer and when it gets dirty inside, it can report erroneous data that can cause the computer to cause a low idle condition. The TPS can't be cleaned though, it needs to be replaced if it goes bad.

 

Now, after all of the technical advice, here is a layman's solution: SEAFOAM!

In all seriousness, I would try a thorough cleaning with Seafoam to see if that cleaned out whatever it is that is causing the problem....

 

What makes you believe the magical mystical Sea Foam is any better than any good quality throttle body cleaner Paul? I mean if it's already squeaky clean after using TB cleaner as mine always is, is SF going to somehow get it any cleaner inside there?

 

I just like all the pretty white smoke.

 

Here is an ideal to check. I had a friend's Dodge Ram with a similar problem. I replaced the idle air control for her car but it continued to die when at a stop. I drove it for a few days to figure out what was wrong with it. I noticed it only died when the engine was warm. I took a wild guess and replaced the temperature sensor. Her truck has been working ever since then.

Hope that helps.

 

thanks guys, I'll try those sensors & see what happens.

 

No one ever posts the final resolution... What was the issue? This sounds similar to my problems.

 

Exactly, and now it's 3 years later and I am having this same problem. If you post a question on these forums looking for a solution, make sure you post the answer.

 

I'm having similar issues with my 04 auto.

Wonder what it is about the auto that seems to have more problems. Maybe something with the torque converter.

 

How about crank position sensor. Had idle problems along with cutting out every once in a while. Cleaned the throttle body and all the sensor but still had problem. Read somewhere on the forum to change CPS and that fixed my problem.

 

I had a similar issue and the above solution solved my issue. Fortunately, I was able to get the check engine code pointing to the CPS.

 

When you cleaned the throttle body did you also pull the IAC and clean it, the plunger, and the tube for the plunger? That's what I would start with.

 

I've replaced every sensor mentioned on here, cleaned the TB, replaced most of the valves, and I'm still dealing with this.
I'm going back into the transmission next to try replacing fluid and filters... again. This time trying this Lucas oil miracle juice that they gave me at NAPA. I'm out of options, more importantly my wife's out of patience. If this doesn't work it's going to the shop, and I'm grabbing my ankles, and biting a stick.

 

I'm also having this problem. I have replaced the IAC and the TPS. No change.
It does seem to be okay when the engine is cold, it just gets worse when it has warmed up. Maybe the temp sensor is the fix. I may try that since they are cheap. I tried to reset the computer by grounding the pos lead of the battery, no change except that it may have gotten worse. I have noticed that when it is idling very low, like 250, if I touch the accelerator, the rpm will go back up and stay there. Weird.

 

a new temperature sensor didnt fix my rough idle. I'm still trying to track this down myself.

New IAC, Air Temp sensor, Camshaft sensor, TB is clean as a whistle, Injectors are clean, Air filter clean, spark plugs properly gapped.

my next steps are going to be new camshaft synchronizer, new plugs and possibly a new coil rail, and map sensor

i'm starting to think this might be more of a mechanical failure vs an electrical one. FRUSTRATING as all hell though:thumbdown:

 

Check the IAC.

 

With all the reports of this problem where a new IAC and TPS isn't fixing it, the problem is elsewhere. There are a few possibilities, the main computer needs reflashing is one, the intake air sensor, the manifold absolute pressure sensor. Since mine seems to develop th eproblem after warm up, it may be temp related, which could point to the intake air sensor. The only confusing thing to me is that when I blip the throttle when it's idling low, the idle will pick back up and stay. This kind of points to the absolute pressure sensor being tired. When blipping the throttle, the vacuum drops and then spikes and this may fix the idle.

 

Most of the posts above mention everything but the throttle position sensor (actually, it is mentioned on page one). If this potentiometer gets a dead spot in the resting position (foot off the gas pedal), then the computer has no idea what the throttle position is and may not command the IAC to open when it should...I have HPTuners programmer/scanner/datalogger that I've been using for tuning Corvettes, and it works well enough on my jeep to scan and show me the tps, map, spark etc. Maybe a good OBDII scanner would help diagnose??

 

I decided to replace the manifold absolute pressure sensor as the low idle seemed to be sensitive to vacuum. It didn't fix it. I have replaced the CPS, the TPS, the MAP, the IAC. I've had the injectors and throttle body cleaned and checked the fuel pressure. That is just about everything. There are no codes in the computer, so I'm running out of ideas. The derned thing is tuned so well it will idle smoothly at 250 and it runs fine but it just bothers me that it's not idling right.

 

I'm a 72 Hokie myself! I'll keep an eye out while you try out your cam sensor. I saw an article that replacing the speed sensor in the transfer case solved their low idle problem. That one never occured to me. I hate to keep throwing parts at this, my place is starting to look like a warehouse of used sensors. My idlle problem seems different...when its idling at 250, I can blip the throttle and it goes up to 500 and stays. When I turn on the AC, it goes right to 500 and stays so I know the IAC is fine.That makes it an annoying problem to solve.

 

2007 Hokie myself.

the fact that you can tap the throttle and the idle returns back to normal seems like a physical issue to me. Maybe the butterfly valve in the throttle body is getting stuck in the wrong position, or the return spring is sticking. Try putting a tiny drop of oil on the butterfly hinge.

I dont see how the speed sensor would have anything to do with the idle speed. at least my 04 TJ is using a mechanical gear in the tailhousing of the T-case. It is the correct one for the 33" tires i'm running and the speedometer is only off 2-3 MPH. maybe someone can shed some light on this...

i know what you mean about the warehouse of used sensors. I have a pile of boxes on the workbench.

to date i have replaced... IAC, air temperature, Camshaft synchronizer and sensor, spark plugs, TPS. Injectors and TB are clean as a whistle. Crank position sensor was cleaned and reinstalled, I have a replacement, but the old one looked better than the new one.