mpsldr05

What would cause my rpm's to fluctuate when I first start my jeep in the morning? You can her it jump about 500 rm for 10-15 sec then drop back down. Then after I drive it for about 5 mins or so and let it idle it levels out. So naturally when I try to show anyone it never does it. It does it when I put it in drive and pull the e brake and let it sit as well just not as much of a fluctuation or when I'm sitting at a stop light, kind a worries me that it's gonna stall out. I've replaced the crank shaft position sensor and the pickup coil already. New battery new PCM in jan new pcm connectors. The problem started when I jacked it up to put new brakes and rotors on it. As odd as that sounds. Any ideas? I was thinking a faulty throttle position sensors maybe a "blank spot" has developed

kjc

Hi newbie.. Whenever you post a question about your Jeep, you really need to indicate the year/make/model/ engine ID etc. That's because there are so many differences between models, years, engines well, you get the idea. You did do good with the symptoms and the parts you've replaced.

Bustedback

The idle will be higher during a cold start to help get the catalytic converter up to temp sooner.

mpsldr05

My apologies I have a 1998 jeep grand Cherokee limited 4.0

kjc

No need to be sorry, just letting you know.. to get better answers. I wouldn't think the TPS would be the issue on startup. I'd suggest cleaning the IAC. The Idle Air Control is right next to the throttle body and the pintle gets fouled with carbon. It's a major component as far as idle speed. It's easy to remove and clean.. just don't twist the pintle while gently cleaning it. There are other things to check, but IAC is a common issue. Hope this helps.

BigGeorge

Do you have the defrosters on when you notice the idle fluctuating? If so the air conditioner compressor is cycling as it should and causing the rpm's to rise and fall. It will only do it on defrost, all other heater settings will not cause the rpm's to fluctuate.

mpsldr05

It does it all the time, but primarily worse when idle in drive or just started in the morning. i put a new k&n air filter in yesterday, this weekend I'm going to replace the IAC. Or at least attempt to. I have to find where it plugs into, im not one for cutting wires unless I'm left with no choice, I picked up the chilton and Haynes manual figure that should help with replacing and troubleshooting any future issues.

Thanks for all the help and suggestions.

Bustedback

WTF? You never cut any wires under the hood, or anywhere on a vehicle!

mpsldr05

First off when I said cut wires it's not as thou I'm simply cutting and leaving them there, the idea was to cut the wires and re run new using the new connectors, in the past I've had to cut and heat shrink or solder new connections. Second off "never cut wires" is a little dramatic, there are times where it's simply cost effective or a better use of time to cut and run new. Of course you have to remove what you cut. And of course you have to drain the system of all residual power.

Bustedback

Yes, it is acceptable to cut damaged wiring and replacing with new properly terminated wiring, but to just cut the wiring instead of disconnecting from wherever it plugs onto is just plain lazy and stupid.

celicoupe

The symptoms you described sound like normal operation to me....

mpsldr05

I cleaned the aic and sea foamed the engine and it made a dramatic difference. Thank you all for your help