mattjoness

Hello all. I have a 2000 Cherokee sport that has been rough idling without a check engine light. It will only rough idle when it is stopped and runs fine when i'm on the gas; when stopped it'll idle at about 500-600 RPMS and sputter like it wants to stall. The spark plugs and coils are new, the throttle body has been cleaned and the gasket has been replaced. I've checked for leaks the best that I can, but I've read the the 2000's will throw a code if there is a leak. Any suggestions?

Turbo X_J

What's the fuel pressure in psi? Have you performed a compression test? Have you scanned the vehicle for codes?

mattheww97

What is the condition of your fuel injectors? I'm currently waiting for my 4 hole upgraded injectors to come in the mail. It's supposed to improve gas mileage and over all performance of the vehicle

Noah Wallace

I've got a 97 country that when idling it will surge up to about 1100 for several seconds then go back down to maybe 800. I was having worse problems including a couple stalls when approaching a stop, but did a few things that I thought cleared it up. Now it's revving up to about 1000-1100 just sitting here, then down again but not bogging.

I've recently:
cleaned throttle body
cleaned idle air control valve
new throttle position sensor
fuel pressure test, showed about 43 psi
checked injectors, all were clicking good

I bought an o2 sensor and for the life of me could not get the old one off, almost rounded off the hex. Yes I've tried running it to where the pipe is warm but not quite the sensor warm. But I haven't had a check engine light in ages. So I returned the sensor, this was in September. Last night I ordered another one thinking it wouldn't hurt to get a new one even though no code being thrown. Again could not get the old one off.

I'm still convinced there's something wrong with the fuel system. 6 years ago as a novice I bought a new fuel pump kit on eBay and had a mechanic throw it in because my dash gauge wasn't working properly. Ever since then I can only put in 15-16 gallons max (20 gallon tank) so I just figured it was the float. But when I fill up, my gauge shows half of a tank after maybe 50 miles. Then the another 120-150 miles before the gas light comes on. I'm sure there's still 5 gallons in there at that point, but less than 200 miles per tank can't be right. On a trip home from the cabin, just once, I got around 350 miles on that tank. Yes it was cruise control but I use cruise every day to and from work, and still, that's way more than 180-200 miles.

anyway, the surging/ high idle, could it all be related?

thanks!!

PatHenry

Did you clean and tighten all your grounds? There are 2 in the trunk -drivers side behind the trim panel that are often overlooked.

Are you certain the pump was the correct part? Sure it COULD be related, but if it's been 6 years and the idle thing started recently I'd consider them 2 separate issues for now.

Is that psi in spec, I thought 97 was supposed to be higher.. I'd double check the spec value.

Noah Wallace

well I'm not 100% sure it is the right pump, or had a compatible sending unit, I was not as in tune to the vehicle as I am now. Yeah they could be unrelated issues, but the fuel economy/ amount of gas I put in has been this way the whole time, only the surging is new.

I thought the 97 was supposed to be higher too but looked at a few forums while doing the test and everyone was saying around 43 give or take a few.

now that you mention it, I've never really checked the grounds. The one or two under the hood I have looked at, maybe checked for tightness, but never noticed anything.

PatHenry

I saw another thread and 43 is basically right at the bottom of spec.

Definitely check the trunk grounds. There are many threads of "gremlin" chasing, bogging down and hesitation issues that the root cause was those grounds being corroded.

I know that at least one of the trunk grounds is directly involved in fuel pump operation, so you definitely want that well grounded.

Noah Wallace

ooh really? Wow, thanks. But that doesn't necessarily need to be replaced, right? Just cleaned up?

PatHenry

No replacement, just get the mating surfaces nice and Shiney and the bolts nice and tight. Since this is an easy and free thing to do it just makes sense that if you have any electrical issue to check grounds.

Noah Wallace

right. I feel a little dumb I haven't thought of that considering I work with and studied electrical systems. Oops

PatHenry

I actually had no idea about the grounds in the trunk, but was reading an old thread and the OP was having a terrible time with bogging down and literally he cleaned up those grounds and viola - engine ran great. Since I would never have thought to look for grounding wires there, I always mention it.

Noah Wallace

forgot to mention it's always worse when its really cold. I live in Minnesota and it's been below zero for basically 3 weeks with a couple warmer days.

PatHenry

It's been nearly that bad in MA as well.
After you check/clean grounds and check the compression as Turbo suggested, if you still have the problem I'd talk to Jordan96xj and put an OBD2 tool on it and check fuel trims and all that.

On a side note - Go vikings!

PatHenry

Oh, and you might want to throw some drygas in it to make sure you don't have any moisture in the gas tank.

Noah Wallace

yes! Skol Vikings indeed! It's a very exciting time to be a mn sports fan, we're so used to being let down.

ground connections in trunk looked good, clean and tight. But I did notice behind that area where all the wires are tucked in and such, that there was moisture and dirt. The inside of that wheel well is pretty rusty, I've never noticed it on the outside. Turns out some of the rust along the rocker panel, though I knew that was rusted through, was also rusted through a bit behind the wheel. Basically with a flashlight looking into that area with all the wires, I spotted my garage floor....

again the connections were dry behind the spare, but everything behind that part of the frame was damp...