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dzJeepChic

ScottLs 2001 XJ

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Driving up to the top of the mountain at Cinders last weekend my Jeep started idling very low & began shaking. Then once we got to the last steep hill before the top it died. I could start it back up but it wouldn't hold idle unless I put my foot on the gas a little to keep the rpm's up. Plugged in my OBDII code reader & surprisingly the jeep passed inspection with no codes thrown. Kevin & Kris thought to disconnect my battery to reset the computer so we tried that leaving it unhooked for about 5 minutes. After reconnecting my battery the jeep fired up holding idle, a little low at around 450-500 rpms, but the shaking & dying stopped so I could get off the trail & subsequently home.

 

Back home I googled low idle issue for Cherokees. Funny thing is there are tons of threads about the subject & many more subsequent fix suggestions, however, I could not find one with a definite resolution. More of the type that reads, "..thanks for the tip, i'll try it tonight and report back the result." Only they never posted whether or not the suggestion really fixed their issue. I also read, "oh that's probably the MAP sensor" & "try cleaning the IAC w/ carb cleaner, it's a cost free fix." But no one I could find ever posted what the real fix was.

Ultimately I ended up cleaning out my throttle body with air intake cleaner & replaced the MAP, IAC & TPS

2D820281-2C67-4851-9483-6D647BF7A0A8_zpsoiavmfrc.jpg

They were dirty & the orifices filled with brownish sludge. I remembered replacing the MAP sensor a while back but noticed a tab busted off where the pigtail plugs into it so I went straight back to the zone for another one while I had everything apart to be safe

AAE43768-8197-4A8D-863E-E0B34B580CE5_zpse8qpxacn.jpg

Also picked up a spare idler pully because you never know..

F5890E72-0871-44FF-A964-1DB3BDF2EDCC_zpsevskf0sd.jpg

Lastly, I cleaned my very dusty K&N filter & buttoned everything back up in just in time for bed last night

202C254A-B7D8-4ADA-ADF9-00539262A93E_zpsirqxmyn0.jpg

So far so good. Drove the jeep to work today and it ran great, idling above 900 rpm's at startup. After heat soak & sitting at a traffic stop with my foot on the brakes rpm's will drop to 750 but that's the way I have always remembered it idling.

Thank you to Kevin, Kris, George and all others who waited patiently for me to fix my junk, er jeep while stuck on the mountain.

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This week I've noticed my Jeep idling below normal levels again. Not as bad as the incident at Cinders where the vehicle would shimmy & shake but it's idling below the third mark (750 rpms?) like in this photo F6E4F939-9F26-4699-A01C-BD8C5C3827E6_zpsyseepslk.jpg

Sometimes idle drops to the second hash mark when stopped at a traffic light which sucks.

The fuel pump was R&R'd back in November 2013 & I've replaced every sensor that would effect idle since then except the Manifold Temperature sensor & Coolant temperature sensor.

Seeing that my temperature gauge works properly I decided to switch out the manifold temperature sensor yesterday

3C78B5BD-CF44-4351-88E0-B31FCA9B02C9_zpsriqpt2n0.jpg

The old one looked fried

68743812-2F01-4741-A0E4-34FC630847E9_zpsg13kpphj.jpg

Honestly, I couldn't tell whether or not the old one really was bad but the jeep did idle well above 750 today on the way to work. Hopefully this time it will last longer than 2 weeks.

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Hope that works.

 

G:cool:

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Have you checked fuel pressure and the fuel for air?

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Have you checked fuel pressure and the fuel for air?

 

Not yet. I don't see a fuel pressure regulator on the fuel line so guessing I'd have to purchase an aftermarket one and mount it somewhere?

Also, how would I check the fuel for air? I know my gas cap recently passed emissions inspection but otherwise never heard of that being a potential problem for idle issues.

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Fuel regulator is either on the fuel rail or mounted to the top of the pump assembly (in the tank). You can check for air in the fuel by hooking up fuel pressure gauge and using the valve on the gauge assembly if you see bubbles in the fuel you have air (more than likely not the problem). I would also check for vacuum leaks they can cause rough idling. Most sensors when bad will have a code pop up if they are outside of the acceptable parameters. Since they are monitored by the ecm for emissions controls. A bad gas cap would more than likely cause a small leak code in evap system (I think it is the evap system).

 

Just my thoughts.

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Scott, there should be a Schrader valve on the fuel rail which has threads on it. You can get a pressure gauge from Autozone or O'Rilley and hook it on there. You can also bleed the fuel lines there. Pressure should be between 41-46 lbs

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Fuel regulator is either on the fuel rail or mounted to the top of the pump assembly (in the tank). You can check for air in the fuel by hooking up fuel pressure gauge and using the valve on the gauge assembly if you see bubbles in the fuel you have air (more than likely not the problem). I would also check for vacuum leaks they can cause rough idling. Most sensors when bad will have a code pop up if they are outside of the acceptable parameters. Since they are monitored by the ecm for emissions controls. A bad gas cap would more than likely cause a small leak code in evap system (I think it is the evap system).

 

Just my thoughts.

 

Thanks Mike, I'll check the pressure & report back.

 

Scott, there should be a Schrader valve on the fuel rail which has threads on it. You can get a pressure gauge from Autozone or O'Rilley and hook it on there. You can also bleed the fuel lines there. Pressure should be between 41-46 lbs

 

Thanks Loren, good to know.

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i have a fuel pressure gauge that will attach to your rail, you can come by some afternoon and we'll check her out if you'd like

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i have a fuel pressure gauge that will attach to your rail, you can come by some afternoon and we'll check her out if you'd like

 

Thank you for the offer. Got my oil changed yesterday & decided to have the shop check fuel pressure. They reported:

 

  • Key on Engine Off pressure - 47psi
  • Key on Engine Running pressure - 49psi
  • No leak down detected after 5 minutes
  • Fuel Pressure is within manufacturer spec of 49.5psi(+/-5psi)

Future Recommendation

-Fuel System Service

-Engine Decarb/Carbon Cleaning

 

"Fuel System Service" involves hooking up a line of chemical solvent to the fuel rail & running the vehicle which would clean the entire fuel system of varnish & other residue from the weird additives they put in gas nowadays. Last time I had the decarb/cleaning service performed was March 2009. They recommend both be done since it's been 6+ years on the decarb. Both services are on the expensive side north of $300 & it'd be frustrating having forked out all that cash replacing sensors on top of this only to have the idle return back to where it is now a few weeks down the road.

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