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angelas817 · 08-23-2010, 05:36 PM

I sure hope someone can help

! My husband has a 2000 Jeep Grand Cherokee Limited 4.7 with an idle issue?? Everytime he starts his car the rpms rev up then drop then rev then drop....he said it also does this when highway driving. He sets his cruise and watches the rpms go up then down (it has not stalled and is not tripping any codes) He thought it might be the TPS,so he hooked up the volt meter,set it to 20k and got a smooth increase up to 4 (it didn't go any higher). Checked voltage to TPS and got a reading of about 5 volts and an increase up to almost 5 volts when throttle was opened. Has anyone had a similiar problem or have ANY ideas what the problem might be??

jeepgod · 08-23-2010, 07:43 PM

I do not know about the V8 G.C. throttle position sensors but it would be wise to get a chilton's manual as it will tell you the parameters for them and how to check them properly. It could be the TPS or the IAC (Idle Air Control Valve) if equipped. It could also be other sensors too, this is why getting the manual will help because it will tell you how to check all of the sensors to tell if they are bad or not.

Mud_Pig · 08-24-2010, 09:51 AM

I would start by cleaning the throttle body. Go to your local dealer and get a can of throttle body cleaner (vu01446) and an old toothbrush. Romove the intake tube from the throttle body and clean up all the carbon in there, spray the remainder of the can into the throttle body and let sit for about 10 minutes, then start the jeep and rev a few times to clean out any deposits and it should idle better.

jeepgod · 08-24-2010, 10:43 AM

I would nto recommend cleaning your throttle body with a tooth brush while it is still on the engine as you may get large chunks of deposite in your engine and it could cause scoring or other damage to it......if you clean your throttle body, a simple carbon cleaner and tooth brush will do the same job as the stuff from the dealer.

angelas817 · 08-24-2010, 11:09 AM

Thank you so much for the suggestions! I am on my way to tell DH now!

RollMeAway · 10-19-2010, 07:17 AM

Hi, If the system is responding to a vacuum leak, it only takes a few seconds to check this. Attach a flex hose to a propane torch and turn it on. (Do not light Torch!!!!) (Make sure engine is running!) Put the hose near all the plumbing and in the tight areas where they connect. The engine will immediately smooth out or change idle if it sucks in the propane. Even though I like to try stuff to fix things, I like to instead, do tests to isolate the problem. 'Saves from pissing away time and money. (Some restrictions may apply, your mileage may very, no salesman will call allow 4-6 weeks for delivery, objects in mirror may be closer than they appear...)

**WJCraig** · 10-19-2010, 08:24 PM

Might want to add in "Not to light the torch"...a lot of people read this stuff, and not all of them may realize you just want the gas to get sucked in. Also works with different aerosols like throttle body cleaner, or other engine solvents at the auto parts stores...

RollMeAway · 10-20-2010, 05:22 AM

Thanks for the tip WJC!
RMA

**WJCraig** · 10-21-2010, 09:53 PM

No problem. Anyway, the first thing I'd look at doing is scanning for any codes. O2 Sensors can cause so many different problems and they are more often then not the trouble maker, and they are fairly easy to replace.

RollMeAway · 10-22-2010, 05:43 AM

Good point WJC, sometimes it's tough to see the forest through the trees! It's logical and an efficient use of time to check the codes!