2001 GMC Jimmy 4.3L rough idle lean condition


Asked by Dec 05, 2013 at 10:32 PM about the 2001 GMC Jimmy 2 Dr SLS SUV

Question type: Maintenance & Repair

I have an 2001 gmc jimmy 4.3 l while driving home it started running rough and stalled out but would start back up but idles rough and when I put in gear it runs worse and stalls I found there was a fuel leak in the upper manifold and the fuel pressure was 53 psi. with a bad misfire on 1 and 2 cylinder I replaced the spider and the pressure regulator. it still idles  rough and the long fuel trims show 25%  so its requesting more fuel a lean condition but goes to normal when you bring the RPMs to 1000 and up I have looked for vacuum leaks and can't find any. fuel pressure is now up to 55 psi. could the pump cause this or what do you think this is.

8 Answers


I had replaced the spark plugs and wires no change in the way it runs. I also tried the unplugging the MAF and there was no change. I did find a leak in the exhaust just past the O2 sensor so I will be fixing that next. if any one has any thing to add I'm open to other fixes

5 of 5 people found this helpful.

is there not a fuel pressure regulator...accessing, accessing...

3 of 3 people found this helpful.

the new spider I bought came with a new fuel pressure regulator on it already

2 of 2 people found this helpful.

I put in the new fuel pump and the pressures are right and it acts as it should now when you snap the throttle but it still is missing and running rough at idle its showing a lean condition at idle but then my starter went out so I need to fix that to continue the diagnosis any other help my ears are open

2 of 2 people found this helpful.

roy, the spider assembly has a regulator on it. make sure the intake plenum (tubing between maf and throttle body) is in good shape. Any air entering here will cause a lean condition. Your fuel pressure is spot on. Also take your brake booster line off and plug it. I've had a leaky booster before.

2 of 2 people found this helpful.

just an update the distributer cap was cross firing on the in side on 1 and 2 cylinders causing the miss fire but with the spark test you would still have spark just not firing at the right time causing a miss fire on those two cylinders. causing a lean condition. replaced that and it runs good now

3 of 3 people found this helpful.

as long as I'm a guessin' fool...am going to suggest an intake air temperature sensor may be playin' hell with the mix~ http://www.autopartswarehouse.com/sku/GMC/Jimmy/Standard/IAT_Sens or/2001/SIAX32.html? apwcid=productads&003=27846857&010=apwSIAX322001gmjiiase&gcl id=CNOckZ2F4LsCFa9cMgodpXEA2Q

2 of 2 people found this helpful.

another zinger is the Idle air control~ https://www.google.com/#q=2001+GMC+Jimmy+4.3L+idle+air+control&tbm =shop

4 of 4 people found this helpful.

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