High idle at startup
Asked by Dave Feb 11, 2019 at 04:30 AM about the 2001 Jeep Grand Cherokee Laredo 4WD
Question type: General
My 01 jeep grand Cherokee 4.0 recently started
idling high when started around 1500-2,000rpms
and it doesn't come down sometimes it will
actually go higher like someone is punching the
gas and has to be shutoff. the idle stats high
whether in park or gear I have put a new IAC,spark
plugs,cleaned the throttle body and put a new
gasket on it and put another TPS on when I put my
brother's diagnostic computer on it it reads the
absolute throttle position at 12.8% with 2 different
TPS during key on engine off there are no vacuum
leaks that I can here it has a newer ECM and the
motor only has around 40,000 on a rebuild from
Chrysler from previous owner I was thinking about
replacing the TPS pigtail connector but it is like
$50 and don't want to do it just to do it any
suggestions?
9 Answers
Hornet_2497 answered 5 years ago
Scan for codes and see what comes up. Look again for vacuum leaks. On these engines I've seen loose intake manifold bolts, leaky/missing hoses that plug into the intake manifold, leaky cruise control modules, etcetera. Pinch off vacuum hoses as a test for excessive vacuum consumption.
Hornet_2497 answered 5 years ago
And check that fat hose supplying vacuum to your brake booster. The diaphragm might have a massive vacuum leak. Pull the hose from the canister and plug it off.
Ok it brings up a code for the vehicle speed sensor and for the throttle position sensor but I switched the throttle position sensor do you think it can be the plug going to it it reads 5v going to it with a multimeter but sometimes if you move it a little the idle will shoot up like someone is almost flooring it.I read somewhere else about the booster but when I put a vice grip on it there was no change in the idle is it better to pull the hose and plug it?
Hornet_2497 answered 5 years ago
Maybe clear your codes with scanner or disconnecting the battery and see if it comes back. The most relevant code is the TPS. The 5 volts is the normal input voltage to a sensor. And pinching off that vacuum booster hose is an okay test too. But put it back when done. If I think of anything else I will post it. It will be something simple like a loose ground or connector.
Ok thanks for your advice
My 2003 G. C. Laredo had a similar problem - idle jumped to approximately 2000 rpm and just would not drop down. My 4.0L engine has an Idle Air Control Valve on the throttle body. It is a motor-driven shaft that controls the idle air flow as the engine warms up. At 169K miles it was all "junked" up with carbon deposits, etc. I replaced the valve and my Jeep is now idling normally.
Just replaced idle air control value got code p0505 idle air control value replacer value and started. Idleing at 2000 rpms and higher only way to stop going higher rpms had to shut off didn't do this before replaced it please help me whats up with it
Just replaced idle air control value on 04 jeep grand Cherokee 4.0 got code p0505 idle air control value replacer value and started. Idleing at 2000 rpms and higher only way to stop going higher rpms had to shut off didn't do this before replaced it please help me whats up with it
You're wasting tyime and money replacing IAC with anything but the expensive Mopar one. My orig. IAC lasted 200000 miles. It was replaced by a Standard that lasted about 1000 miles and then the idle started hanging up at 1500 rpm +. I could get it back down by a quick off/on of the ignition. It was replaced by a 97$ Mopar IAC and now the idle stays where it should and it actually runs better. Amazon has Jeep IACs for 12$ on up. There has to be something different with the Mopar one besides price.
